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Leptonica 1.85.0
Image processing and image analysis suite
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Leptonica 1.85.0
Image processing and image analysis suite
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#include <string.h>#include <math.h>#include "allheaders.h"Go to the source code of this file.
Functions | |
| static l_ok | findHistoGridDimensions (l_int32 n, l_int32 w, l_int32 h, l_int32 *pnx, l_int32 *pny, l_int32 debug) |
| static l_ok | pixCompareTilesByHisto (PIX *pix1, PIX *pix2, l_int32 maxgray, l_int32 factor, l_int32 n, l_float32 *pscore, PIXA *pixadebug) |
| l_ok | pixEqual (PIX *pix1, PIX *pix2, l_int32 *psame) |
| l_ok | pixEqualWithAlpha (PIX *pix1, PIX *pix2, l_int32 use_alpha, l_int32 *psame) |
| l_ok | pixEqualWithCmap (PIX *pix1, PIX *pix2, l_int32 *psame) |
| l_ok | cmapEqual (PIXCMAP *cmap1, PIXCMAP *cmap2, l_int32 ncomps, l_int32 *psame) |
| l_ok | pixUsesCmapColor (PIX *pixs, l_int32 *pcolor) |
| l_ok | pixCorrelationBinary (PIX *pix1, PIX *pix2, l_float32 *pval) |
| PIX * | pixDisplayDiff (PIX *pix1, PIX *pix2, l_int32 showall, l_int32 mindiff, l_uint32 diffcolor) |
| PIX * | pixDisplayDiffBinary (PIX *pix1, PIX *pix2) |
| l_ok | pixCompareBinary (PIX *pix1, PIX *pix2, l_int32 comptype, l_float32 *pfract, PIX **ppixdiff) |
| l_ok | pixCompareGrayOrRGB (PIX *pix1, PIX *pix2, l_int32 comptype, l_int32 plottype, l_int32 *psame, l_float32 *pdiff, l_float32 *prmsdiff, PIX **ppixdiff) |
| l_ok | pixCompareGray (PIX *pix1, PIX *pix2, l_int32 comptype, l_int32 plottype, l_int32 *psame, l_float32 *pdiff, l_float32 *prmsdiff, PIX **ppixdiff) |
| l_ok | pixCompareRGB (PIX *pix1, PIX *pix2, l_int32 comptype, l_int32 plottype, l_int32 *psame, l_float32 *pdiff, l_float32 *prmsdiff, PIX **ppixdiff) |
| l_ok | pixCompareTiled (PIX *pix1, PIX *pix2, l_int32 sx, l_int32 sy, l_int32 type, PIX **ppixdiff) |
| NUMA * | pixCompareRankDifference (PIX *pix1, PIX *pix2, l_int32 factor) |
| l_ok | pixTestForSimilarity (PIX *pix1, PIX *pix2, l_int32 factor, l_int32 mindiff, l_float32 maxfract, l_float32 maxave, l_int32 *psimilar, l_int32 details) |
| l_ok | pixGetDifferenceStats (PIX *pix1, PIX *pix2, l_int32 factor, l_int32 mindiff, l_float32 *pfractdiff, l_float32 *pavediff, l_int32 details) |
| NUMA * | pixGetDifferenceHistogram (PIX *pix1, PIX *pix2, l_int32 factor) |
| l_ok | pixGetPerceptualDiff (PIX *pixs1, PIX *pixs2, l_int32 sampling, l_int32 dilation, l_int32 mindiff, l_float32 *pfract, PIX **ppixdiff1, PIX **ppixdiff2) |
| l_ok | pixGetPSNR (PIX *pix1, PIX *pix2, l_int32 factor, l_float32 *ppsnr) |
| l_ok | pixaComparePhotoRegionsByHisto (PIXA *pixa, l_float32 minratio, l_float32 textthresh, l_int32 factor, l_int32 n, l_float32 simthresh, NUMA **pnai, l_float32 **pscores, PIX **ppixd, l_int32 debug) |
| l_ok | pixComparePhotoRegionsByHisto (PIX *pix1, PIX *pix2, BOX *box1, BOX *box2, l_float32 minratio, l_int32 factor, l_int32 n, l_float32 *pscore, l_int32 debugflag) |
| l_ok | pixGenPhotoHistos (PIX *pixs, BOX *box, l_int32 factor, l_float32 thresh, l_int32 n, NUMAA **pnaa, l_int32 *pw, l_int32 *ph, l_int32 debugindex) |
| PIX * | pixPadToCenterCentroid (PIX *pixs, l_int32 factor) |
| l_ok | pixCentroid8 (PIX *pixs, l_int32 factor, l_float32 *pcx, l_float32 *pcy) |
| l_ok | pixDecideIfPhotoImage (PIX *pix, l_int32 factor, l_float32 thresh, l_int32 n, NUMAA **pnaa, PIXA *pixadebug) |
| l_ok | compareTilesByHisto (NUMAA *naa1, NUMAA *naa2, l_float32 minratio, l_int32 w1, l_int32 h1, l_int32 w2, l_int32 h2, l_float32 *pscore, PIXA *pixadebug) |
| l_ok | pixCompareGrayByHisto (PIX *pix1, PIX *pix2, BOX *box1, BOX *box2, l_float32 minratio, l_int32 maxgray, l_int32 factor, l_int32 n, l_float32 *pscore, l_int32 debugflag) |
| l_ok | pixCropAlignedToCentroid (PIX *pix1, PIX *pix2, l_int32 factor, BOX **pbox1, BOX **pbox2) |
| l_uint8 * | l_compressGrayHistograms (NUMAA *naa, l_int32 w, l_int32 h, size_t *psize) |
| NUMAA * | l_uncompressGrayHistograms (l_uint8 *bytea, size_t size, l_int32 *pw, l_int32 *ph) |
| l_ok | pixCompareWithTranslation (PIX *pix1, PIX *pix2, l_int32 thresh, l_int32 *pdelx, l_int32 *pdely, l_float32 *pscore, l_int32 debugflag) |
| l_ok | pixBestCorrelation (PIX *pix1, PIX *pix2, l_int32 area1, l_int32 area2, l_int32 etransx, l_int32 etransy, l_int32 maxshift, l_int32 *tab8, l_int32 *pdelx, l_int32 *pdely, l_float32 *pscore, l_int32 debugflag) |
Variables | |
| static const l_float32 | TINY = 0.00001f |
Test for pix equality
l_int32 pixEqual()
l_int32 pixEqualWithAlpha()
l_int32 pixEqualWithCmap()
l_int32 cmapEqual()
l_int32 pixUsesCmapColor()
Binary correlation
l_int32 pixCorrelationBinary()
Difference of two images of same size
l_int32 pixDisplayDiff()
l_int32 pixDisplayDiffBinary()
l_int32 pixCompareBinary()
l_int32 pixCompareGrayOrRGB()
l_int32 pixCompareGray()
l_int32 pixCompareRGB()
l_int32 pixCompareTiled()
Other measures of the difference of two images of the same size
NUMA *pixCompareRankDifference()
l_int32 pixTestForSimilarity()
l_int32 pixGetDifferenceStats()
NUMA *pixGetDifferenceHistogram()
l_int32 pixGetPerceptualDiff()
l_int32 pixGetPSNR()
Comparison of photo regions by histogram
l_int32 pixaComparePhotoRegionsByHisto() -- top-level
l_int32 pixComparePhotoRegionsByHisto() -- top-level for 2
l_int32 pixGenPhotoHistos()
PIX *pixPadToCenterCentroid()
l_int32 pixCentroid8()
l_int32 pixDecideIfPhotoImage()
static l_int32 findHistoGridDimensions()
l_int32 compareTilesByHisto()
l_int32 pixCompareGrayByHisto() -- top-level for 2
static l_int32 pixCompareTilesByHisto()
l_int32 pixCropAlignedToCentroid()
l_uint8 *l_compressGrayHistograms()
NUMAA *l_uncompressGrayHistograms()
Translated images at the same resolution
l_int32 pixCompareWithTranslation()
l_int32 pixBestCorrelation()
For comparing images using tiled histograms, essentially all the
computation goes into deciding if a region of an image is a photo,
whether that photo region is amenable to similarity measurements
using histograms, and finally the calculation of the gray histograms
for each of the tiled regions. The actual comparison is essentially
instantaneous. Therefore, with a large number of images to compare
with each other, it is important to first calculate the histograms
for each image. Then the comparisons, which go as the square of the
number of images, actually takes no time.
A high level function that takes a pixa of images and does
all comparisons, pixaComparePhotosByHisto(), uses this split
approach. It pads the images so that the centroid is in the center,
which will allow the tiles to be better aligned.
For testing purposes, two functions are given that do all the work
to compare just two photo regions:
* pixComparePhotoRegionsByHisto() uses the split approach, qualifying
the images first with pixGenPhotoHistos(), and then comparing
with compareTilesByHisto().
* pixCompareGrayByHisto() aligns the two images by centroid
and calls pixCompareTilesByHisto() to generate the histograms
and do the comparison.
Definition in file compare.c.
| [in] | cmap1 | |
| [in] | cmap2 | |
| [in] | ncomps | 3 for RGB, 4 for RGBA |
| [out] | psame |
Notes:
(1) This returns same = TRUE if the colormaps have identical entries.
(2) If ncomps == 4, the alpha components of the colormaps are also
compared.
Definition at line 477 of file compare.c.
Referenced by pixEqualWithCmap().
| l_ok compareTilesByHisto | ( | NUMAA * | naa1, |
| NUMAA * | naa2, | ||
| l_float32 | minratio, | ||
| l_int32 | w1, | ||
| l_int32 | h1, | ||
| l_int32 | w2, | ||
| l_int32 | h2, | ||
| l_float32 * | pscore, | ||
| PIXA * | pixadebug ) |
| [in] | naa1,naa2 | each is a set of 256 entry histograms |
| [in] | minratio | requiring image sizes be compatible; < 1.0 |
| [in] | w1,h1,w2,h2 | image sizes from which histograms were made |
| [out] | pscore | similarity score of histograms |
| [in] | pixadebug | [optional] use only for debug output |
Notes:
(1) naa1 and naa2 must be generated using pixGenPhotoHistos(),
using the same tile sizes.
(2) The image dimensions must be similar. The score is 0.0
if the ratio of widths and heights (smallest / largest)
exceeds a threshold minratio, which must be between
0.5 and 1.0. If set at 1.0, both images must be exactly
the same size. A typical value for minratio is 0.9.
(3) The input pixadebug is null unless debug output is requested.
Definition at line 2785 of file compare.c.
References L_ADD_BELOW, L_CLONE, L_FLATE_ENCODE, and L_INSERT.
Referenced by pixaComparePhotoRegionsByHisto(), and pixComparePhotoRegionsByHisto().
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static |
| [in] | n | max number of grid elements is n^2; typ. n = 3 |
| [in] | w | width of image to be subdivided |
| [in] | h | height of image to be subdivided |
| [out] | pnx | number of grid elements in x direction |
| [out] | pny | number of grid elements in y direction |
| [in] | debug | 1 for debug output to stderr |
Notes:
(1) This determines the number of subdivisions to be used on
the image in each direction. A histogram will be built
for each subimage.
(2) The parameter n specifies the "side" of the n x n grid
of subimages. If the subimages have an aspect ratio larger
than 2, the grid will change, using n^2 as a maximum for
the number of subimages. For example, if n == 3, but the
image is 600 x 200 pixels, a 3x3 grid would have subimages
of 200 x 67 pixels, which is more than 2:1, so we change
to a 4x2 grid where each subimage has 150 x 100 pixels.
Definition at line 2722 of file compare.c.
Referenced by pixCompareTilesByHisto(), and pixDecideIfPhotoImage().
| l_uint8 * l_compressGrayHistograms | ( | NUMAA * | naa, |
| l_int32 | w, | ||
| l_int32 | h, | ||
| size_t * | psize ) |
| [in] | naa | set of 256-entry histograms |
| [in] | w,h | size of image |
| [out] | psize | size of byte array |
Notes:
(1) This first writes w and h to the byte array as 4 byte ints.
(2) Then it normalizes each histogram to a max value of 255,
and saves each value as a byte. If there are
N histograms, the output bytearray has 8 + 256 * N bytes.
(3) Further compression of the array with zlib yields only about
a 25% decrease in size, so we don't bother. If size reduction
were important, a lossy transform using a 1-dimensional DCT
would be effective, because we don't care about the fine
details of these histograms.
Definition at line 3287 of file compare.c.
References L_COPY.
| NUMAA * l_uncompressGrayHistograms | ( | l_uint8 * | bytea, |
| size_t | size, | ||
| l_int32 * | pw, | ||
| l_int32 * | ph ) |
| [in] | bytea | byte array of size 8 + 256 * N, N an integer |
| [in] | size | size of byte array |
| [out] | pw | width of the image that generated the histograms |
| [out] | ph | height of the image |
Notes:
(1) The first 8 bytes are read as two 32-bit ints.
(2) Then this constructs a numaa representing some number of
gray histograms that are normalized such that the max value
in each histogram is 255. The data is stored as a byte
array, with 256 bytes holding the data for each histogram.
Each gray histogram was computed from a tile of a grayscale image.
Definition at line 3353 of file compare.c.
References L_INSERT.
| l_ok pixaComparePhotoRegionsByHisto | ( | PIXA * | pixa, |
| l_float32 | minratio, | ||
| l_float32 | textthresh, | ||
| l_int32 | factor, | ||
| l_int32 | n, | ||
| l_float32 | simthresh, | ||
| NUMA ** | pnai, | ||
| l_float32 ** | pscores, | ||
| PIX ** | ppixd, | ||
| l_int32 | debug ) |
pixaComparePhotoRegionsByHisto()
| [in] | pixa | any depth; colormap OK |
| [in] | minratio | requiring sizes be compatible; < 1.0 |
| [in] | textthresh | threshold for text/photo; use 0 for default |
| [in] | factor | subsampling; >= 1 |
| [in] | n | in range {1, ... 7}. n^2 is the maximum number of subregions for histograms; typ. n = 3. |
| [in] | simthresh | threshold for similarity; use 0 for default |
| [out] | pnai | array giving similarity class indices |
| [out] | pscores | [optional] score matrix as 1-D array of size N^2 |
| [out] | ppixd | [optional] pix of similarity classes |
| [in] | debug | 1 to output histograms; 0 otherwise |
Notes:
(1) This function takes a pixa of cropped photo images and
compares each one to the others for similarity.
Each image is first tested to see if it is a photo that can
be compared by tiled histograms. If so, it is padded to put
the centroid in the center of the image, and the histograms
are generated. The final step of comparing each histogram
with all the others is very fast.
(2) To make the histograms, each image is subdivided in a maximum
of n^2 subimages. The parameter n specifies the "side" of
an n x n grid of such subimages. If the subimages have an
aspect ratio larger than 2, the grid will change, again using n^2
as a maximum for the number of subimages. For example,
if n == 3, but the image is 600 x 200 pixels, a 3x3 grid
would have subimages of 200 x 67 pixels, which is more
than 2:1, so we change to a 4x2 grid where each subimage
has 150 x 100 pixels.
(3) An initial filter gives score = 0 if the ratio of widths
and heights (smallest / largest) does not exceed a
threshold minratio. If set at 1.0, both images must be
exactly the same size. A typical value for minratio is 0.9.
(4) The comparison score between two images is a value in [0.0 .. 1.0].
If the comparison score >= simthresh, the images are placed in
the same similarity class. Default value for simthresh is 0.25.
(5) An array nai of similarity class indices for pix in the
input pixa is returned.
(6) There are two debugging options:
* An optional 2D matrix of scores is returned as a 1D array.
A visualization of this is written to a temp file.
* An optional pix showing the similarity classes can be
returned. Text in each input pix is reproduced.
(7) See the notes in pixComparePhotoRegionsByHisto() for details
on the implementation.
Definition at line 1997 of file compare.c.
References compareTilesByHisto(), L_CLONE, pixGenPhotoHistos(), and SET_DATA_BYTE.
| l_ok pixBestCorrelation | ( | PIX * | pix1, |
| PIX * | pix2, | ||
| l_int32 | area1, | ||
| l_int32 | area2, | ||
| l_int32 | etransx, | ||
| l_int32 | etransy, | ||
| l_int32 | maxshift, | ||
| l_int32 * | tab8, | ||
| l_int32 * | pdelx, | ||
| l_int32 * | pdely, | ||
| l_float32 * | pscore, | ||
| l_int32 | debugflag ) |
| [in] | pix1 | 1 bpp |
| [in] | pix2 | 1 bpp |
| [in] | area1 | number of on pixels in pix1 |
| [in] | area2 | number of on pixels in pix2 |
| [in] | etransx | estimated x translation of pix2 to align with pix1 |
| [in] | etransy | estimated y translation of pix2 to align with pix1 |
| [in] | maxshift | max x and y shift of pix2, around the estimated alignment location, relative to pix1 |
| [in] | tab8 | [optional] sum tab for ON pixels in byte; can be NULL |
| [out] | pdelx | [optional] best x shift of pix2 relative to pix1 |
| [out] | pdely | [optional] best y shift of pix2 relative to pix1 |
| [out] | pscore | [optional] maximum score found; can be NULL |
| [in] | debugflag | <= 0 to skip; positive to generate output. The integer is used to label the debug image. |
Notes:
(1) This maximizes the correlation score between two 1 bpp images,
by starting with an estimate of the alignment
(etransx, etransy) and computing the correlation around this.
It optionally returns the shift (delx, dely) that maximizes
the correlation score when pix2 is shifted by this amount
relative to pix1.
(2) Get the centroids of pix1 and pix2, using pixCentroid(),
to compute (etransx, etransy). Get the areas using
pixCountPixels().
(3) The centroid of pix2 is shifted with respect to the centroid
of pix1 by all values between -maxshiftx and maxshiftx,
and likewise for the y shifts. Therefore, the number of
correlations computed is:
(2 * maxshiftx + 1) * (2 * maxshifty + 1)
Consequently, if pix1 and pix2 are large, you should do this
in a coarse-to-fine sequence. See the use of this function
in pixCompareWithTranslation().
Definition at line 3572 of file compare.c.
Referenced by pixCompareWithTranslation().
| l_ok pixCentroid8 | ( | PIX * | pixs, |
| l_int32 | factor, | ||
| l_float32 * | pcx, | ||
| l_float32 * | pcy ) |
| [in] | pixs | 8 bpp |
| [in] | factor | subsampling factor; >= 1 |
| [out] | pcx | x value of centroid |
| [out] | pcy | y value of centroid |
Notes:
(1) This first does a photometric inversion (black = 255, white = 0).
It then finds the centroid of the result. The inversion is
done because white is usually background, so the centroid
is computed based on the "foreground" gray pixels, and the
darker the pixel, the more weight it is given.
Definition at line 2495 of file compare.c.
References GET_DATA_BYTE.
Referenced by pixCropAlignedToCentroid(), and pixPadToCenterCentroid().
| l_ok pixCompareBinary | ( | PIX * | pix1, |
| PIX * | pix2, | ||
| l_int32 | comptype, | ||
| l_float32 * | pfract, | ||
| PIX ** | ppixdiff ) |
| [in] | pix1 | 1 bpp |
| [in] | pix2 | 1 bpp |
| [in] | comptype | L_COMPARE_XOR, L_COMPARE_SUBTRACT |
| [out] | pfract | fraction of pixels that are different |
| [out] | ppixdiff | [optional] pix of difference |
Notes:
(1) The two images are aligned at the UL corner, and do not
need to be the same size.
(2) If using L_COMPARE_SUBTRACT, pix2 is subtracted from pix1.
(3) The total number of pixels is determined by pix1.
(4) On error, the returned fraction is 1.0.
| l_ok pixCompareGray | ( | PIX * | pix1, |
| PIX * | pix2, | ||
| l_int32 | comptype, | ||
| l_int32 | plottype, | ||
| l_int32 * | psame, | ||
| l_float32 * | pdiff, | ||
| l_float32 * | prmsdiff, | ||
| PIX ** | ppixdiff ) |
| [in] | pix1 | 8 or 16 bpp, not cmapped |
| [in] | pix2 | 8 or 16 bpp, not cmapped |
| [in] | comptype | L_COMPARE_SUBTRACT, L_COMPARE_ABS_DIFF |
| [in] | plottype | gplot plot output type, or 0 for no plot |
| [out] | psame | [optional] 1 if pixel values are identical |
| [out] | pdiff | [optional] average difference |
| [out] | prmsdiff | [optional] rms of difference |
| [out] | ppixdiff | [optional] pix of difference |
Notes:
(1) See pixCompareGrayOrRGB() for details.
(2) Use pixCompareGrayOrRGB() if the input pix are colormapped.
(3) Note: setting plottype > 0 can result in writing named
output files.
Definition at line 967 of file compare.c.
References L_MEAN_ABSVAL, and L_ROOT_MEAN_SQUARE.
Referenced by pixCompareGrayOrRGB(), and pixGetPerceptualDiff().
| l_ok pixCompareGrayByHisto | ( | PIX * | pix1, |
| PIX * | pix2, | ||
| BOX * | box1, | ||
| BOX * | box2, | ||
| l_float32 | minratio, | ||
| l_int32 | maxgray, | ||
| l_int32 | factor, | ||
| l_int32 | n, | ||
| l_float32 * | pscore, | ||
| l_int32 | debugflag ) |
| [in] | pix1,pix2 | any depth; colormap OK |
| [in] | box1,box2 | [optional] region selected from each; can be null |
| [in] | minratio | requiring sizes be compatible; < 1.0 |
| [in] | maxgray | max value to keep in histo; >= 200, 255 to keep all |
| [in] | factor | subsampling factor; >= 1 |
| [in] | n | in range {1, ... 7}. n^2 is the maximum number of subregions for histograms; typ. n = 3. |
| [out] | pscore | similarity score of histograms |
| [in] | debugflag | 1 for debug output; 0 for no debugging |
Notes:
(1) This function compares two grayscale photo regions. It can
do it with a single histogram from each region, or with a
set of spatially aligned histograms. For both cases,
align the regions using the centroid of the inverse image,
and crop to the smallest of the two.
(2) The parameter n specifies the "side" of an n x n grid
of subimages. If the subimages have an aspect ratio larger
than 2, the grid will change, using n^2 as a maximum for
the number of subimages. For example, if n == 3, but the
image is 600 x 200 pixels, a 3x3 grid would have subimages
of 200 x 67 pixels, which is more than 2:1, so we change
to a 4x2 grid where each subimage has 150 x 100 pixels.
(3) An initial filter gives score = 0 if the ratio of widths
and heights (smallest / largest) does not exceed a
threshold minratio. This must be between 0.5 and 1.0.
If set at 1.0, both images must be exactly the same size.
A typical value for minratio is 0.9.
(4) The lightest values in the histogram can be disregarded.
Set maxgray to the lightest value to be kept. For example,
to eliminate white (255), set maxgray = 254. maxgray must
be >= 200.
(5) For an efficient representation of the histogram, normalize
using a multiplicative factor so that the number in the
maximum bucket is 255. It then takes 256 bytes to store.
(6) When comparing the histograms of two regions:
~ Use maxgray = 254 to ignore the white pixels, the number
of which may be sensitive to the crop region if the pixels
outside that region are white.
~ Use the Earth Mover distance (EMD), with the histograms
normalized so that the sum over bins is the same.
Further normalize by dividing by 255, so that the result
is in [0.0 ... 1.0].
(7) Get a similarity score S = 1.0 - k * D, where
k is a constant, say in the range 5-10
D = normalized EMD
and for multiple tiles, take the Min(S) to be the final score.
Using aligned tiles gives protection against accidental
similarity of the overall grayscale histograms.
A small number of aligned tiles works well.
(8) With debug on, you get a pdf that shows, for each tile,
the images, histograms and score.
(9) When to use:
(a) Because this function should not be used on text or
line graphics, which can give false positive results
(i.e., high scores for different images), the input
images should be filtered.
(b) To filter, first use pixDecideIfText(). If that function
says the image is text, do not use it. If the function
says it is not text, it still may be line graphics, and
in that case, use:
pixGetGrayHistogramTiled()
grayInterHistogramStats()
to determine whether it is photo or line graphics.
Definition at line 2961 of file compare.c.
References L_INSERT, pixCompareTilesByHisto(), and pixCropAlignedToCentroid().
| l_ok pixCompareGrayOrRGB | ( | PIX * | pix1, |
| PIX * | pix2, | ||
| l_int32 | comptype, | ||
| l_int32 | plottype, | ||
| l_int32 * | psame, | ||
| l_float32 * | pdiff, | ||
| l_float32 * | prmsdiff, | ||
| PIX ** | ppixdiff ) |
| [in] | pix1 | 2,4,8,16 bpp gray, 32 bpp rgb, or colormapped |
| [in] | pix2 | 2,4,8,16 bpp gray, 32 bpp rgb, or colormapped |
| [in] | comptype | L_COMPARE_SUBTRACT, L_COMPARE_ABS_DIFF |
| [in] | plottype | gplot plot output type, or 0 for no plot |
| [out] | psame | [optional] 1 if pixel values are identical |
| [out] | pdiff | [optional] average difference |
| [out] | prmsdiff | [optional] rms of difference |
| [out] | ppixdiff | [optional] pix of difference |
Notes:
(1) The two images are aligned at the UL corner, and do not
need to be the same size. If they are not the same size,
the comparison will be made over overlapping pixels.
(2) If there is a colormap, it is removed and the result
is either gray or RGB depending on the colormap.
(3) If RGB, each component is compared separately.
(4) If type is L_COMPARE_ABS_DIFF, pix2 is subtracted from pix1
and the absolute value is taken.
(5) If type is L_COMPARE_SUBTRACT, pix2 is subtracted from pix1
and the result is clipped to 0.
(6) The plot output types are specified in gplot.h.
Use 0 if no difference plot is to be made.
(7) If the images are pixelwise identical, no difference
plot is made, even if requested. The result (TRUE or FALSE)
is optionally returned in the parameter 'same'.
(8) The average difference (either subtracting or absolute value)
is optionally returned in the parameter 'diff'.
(9) The RMS difference is optionally returned in the
parameter 'rmsdiff'. For RGB, we return the average of
the RMS differences for each of the components.
(10) Because pixel values are compared, pix1 and pix2 can be equal when:
* they are both gray with different depth
* one is colormapped and the other is not
* they are both colormapped and have different size colormaps
Definition at line 886 of file compare.c.
References pixCompareGray(), pixCompareRGB(), and REMOVE_CMAP_BASED_ON_SRC.
| l_ok pixComparePhotoRegionsByHisto | ( | PIX * | pix1, |
| PIX * | pix2, | ||
| BOX * | box1, | ||
| BOX * | box2, | ||
| l_float32 | minratio, | ||
| l_int32 | factor, | ||
| l_int32 | n, | ||
| l_float32 * | pscore, | ||
| l_int32 | debugflag ) |
pixComparePhotoRegionsByHisto()
| [in] | pix1,pix2 | any depth; colormap OK |
| [in] | box1,box2 | [optional] photo regions from each; can be null |
| [in] | minratio | requiring sizes be compatible; < 1.0 |
| [in] | factor | subsampling factor; >= 1 |
| [in] | n | in range {1, ... 7}. n^2 is the maximum number of subregions for histograms; typ. n = 3. |
| [out] | pscore | similarity score of histograms |
| [in] | debugflag | 1 for debug output; 0 for no debugging |
Notes:
(1) This function compares two grayscale photo regions. If a
box is given, the region is clipped; otherwise assume
the entire images are photo regions. This is done with a
set of not more than n^2 spatially aligned histograms, which are
aligned using the centroid of the inverse image.
(2) The parameter n specifies the "side" of an n x n grid
of subimages. If the subimages have an aspect ratio larger
than 2, the grid will change, using n^2 as a maximum for
the number of subimages. For example, if n == 3, but the
image is 600 x 200 pixels, a 3x3 grid would have subimages
of 200 x 67 pixels, which is more than 2:1, so we change
to a 4x2 grid where each subimage has 150 x 100 pixels.
(3) An initial filter gives score = 0 if the ratio of widths
and heights (smallest / largest) does not exceed a
threshold minratio. This must be between 0.5 and 1.0.
If set at 1.0, both images must be exactly the same size.
A typical value for minratio is 0.9.
(4) Because this function should not be used on text or
line graphics, which can give false positive results
(i.e., high scores for different images), filter the images
using pixGenPhotoHistos(), which returns tiled histograms
only if an image is not text and comparison is expected
to work with histograms. If either image fails the test,
the comparison returns a score of 0.0.
(5) The white value counts in the histograms are removed; they
are typically pixels that were padded to achieve alignment.
(6) For an efficient representation of the histogram, normalize
using a multiplicative factor so that the number in the
maximum bucket is 255. It then takes 256 bytes to store.
(7) When comparing the histograms of two regions, use the
Earth Mover distance (EMD), with the histograms normalized
so that the sum over bins is the same. Further normalize
by dividing by 255, so that the result is in [0.0 ... 1.0].
(8) Get a similarity score S = 1.0 - k * D, where
k is a constant, say in the range 5-10
D = normalized EMD
and for multiple tiles, take the Min(S) to be the final score.
Using aligned tiles gives protection against accidental
similarity of the overall grayscale histograms.
A small number of aligned tiles works well.
(9) With debug on, you get a pdf that shows, for each tile,
the images, histograms and score.
Definition at line 2217 of file compare.c.
References compareTilesByHisto(), and pixGenPhotoHistos().
| [in] | pix1 | 8 bpp gray or 32 bpp rgb, or colormapped |
| [in] | pix2 | 8 bpp gray or 32 bpp rgb, or colormapped |
| [in] | factor | subsampling factor; use 0 or 1 for no subsampling |
Notes:
(1) This answers the question: if the pixel values in each
component are compared by absolute difference, for
any value of difference, what is the fraction of
pixel pairs that have a difference of this magnitude
or greater. For a difference of 0, the fraction is 1.0.
In this sense, it is a mapping from pixel difference to
rank order of difference.
(2) The two images are aligned at the UL corner, and do not
need to be the same size. If they are not the same size,
the comparison will be made over overlapping pixels.
(3) If there is a colormap, it is removed and the result
is either gray or RGB depending on the colormap.
(4) If RGB, pixel differences for each component are aggregated
into a single histogram.
Definition at line 1320 of file compare.c.
References L_NOCOPY, and pixGetDifferenceHistogram().
| l_ok pixCompareRGB | ( | PIX * | pix1, |
| PIX * | pix2, | ||
| l_int32 | comptype, | ||
| l_int32 | plottype, | ||
| l_int32 * | psame, | ||
| l_float32 * | pdiff, | ||
| l_float32 * | prmsdiff, | ||
| PIX ** | ppixdiff ) |
| [in] | pix1 | 32 bpp rgb |
| [in] | pix2 | 32 bpp rgb |
| [in] | comptype | L_COMPARE_SUBTRACT, L_COMPARE_ABS_DIFF |
| [in] | plottype | gplot plot output type, or 0 for no plot |
| [out] | psame | [optional] 1 if pixel values are identical |
| [out] | pdiff | [optional] average difference |
| [out] | prmsdiff | [optional] rms of difference |
| [out] | ppixdiff | [optional] pix of difference |
Notes:
(1) See pixCompareGrayOrRGB() for details.
(2) Note: setting plottype > 0 can result in writing named
output files.
Definition at line 1074 of file compare.c.
References COLOR_BLUE, COLOR_GREEN, COLOR_RED, L_MEAN_ABSVAL, and L_ROOT_MEAN_SQUARE.
Referenced by pixCompareGrayOrRGB(), and pixGetPerceptualDiff().
| l_ok pixCompareTiled | ( | PIX * | pix1, |
| PIX * | pix2, | ||
| l_int32 | sx, | ||
| l_int32 | sy, | ||
| l_int32 | type, | ||
| PIX ** | ppixdiff ) |
| [in] | pix1 | 8 bpp or 32 bpp rgb |
| [in] | pix2 | 8 bpp 32 bpp rgb |
| [in] | sx,sy | tile size; must be > 1 in each dimension |
| [in] | type | L_MEAN_ABSVAL or L_ROOT_MEAN_SQUARE |
| [out] | ppixdiff | pix of difference |
Notes:
(1) With L_MEAN_ABSVAL, we compute for each tile the
average abs value of the pixel component difference between
the two (aligned) images. With L_ROOT_MEAN_SQUARE, we
compute instead the rms difference over all components.
(2) The two input pix must be the same depth. Comparison is made
using UL corner alignment.
(3) For 32 bpp, the distance between corresponding tiles
is found by averaging the measured difference over all three
components of each pixel in the tile.
(4) The result, pixdiff, contains one pixel for each source tile.
Definition at line 1228 of file compare.c.
References COLOR_BLUE, COLOR_GREEN, COLOR_RED, L_MEAN_ABSVAL, and L_ROOT_MEAN_SQUARE.
|
static |
| [in] | pix1,pix2 | 8 bpp |
| [in] | maxgray | max value to keep in histo; 255 to keep all |
| [in] | factor | subsampling factor; >= 1 |
| [in] | n | see pixCompareGrayByHisto() |
| [out] | pscore | similarity score of histograms |
| [in] | pixadebug | [optional] use only for debug output |
Notes:
(1) This static function is only called from pixCompareGrayByHisto().
The input images have been converted to 8 bpp if necessary,
aligned and cropped.
(2) The input pixadebug is null unless debug output is requested.
(3) See pixCompareGrayByHisto() for details.
Definition at line 3086 of file compare.c.
References findHistoGridDimensions(), L_ADD_RIGHT, L_CLONE, L_FLATE_ENCODE, and L_INSERT.
Referenced by pixCompareGrayByHisto().
| l_ok pixCompareWithTranslation | ( | PIX * | pix1, |
| PIX * | pix2, | ||
| l_int32 | thresh, | ||
| l_int32 * | pdelx, | ||
| l_int32 * | pdely, | ||
| l_float32 * | pscore, | ||
| l_int32 | debugflag ) |
| [in] | pix1,pix2 | any depth; colormap OK |
| [in] | thresh | threshold for converting to 1 bpp |
| [out] | pdelx | x translation on pix2 to align with pix1 |
| [out] | pdely | y translation on pix2 to align with pix1 |
| [out] | pscore | correlation score at best alignment |
| [in] | debugflag | 1 for debug output; 0 for no debugging |
Notes:
(1) This does a coarse-to-fine search for best translational
alignment of two images, measured by a scoring function
that is the correlation between the fg pixels.
(2) The threshold is used if the images aren't 1 bpp.
(3) With debug on, you get a pdf that shows, as a grayscale
image, the score as a function of shift from the initial
estimate, for each of the four levels. The shift is 0 at
the center of the image.
(4) With debug on, you also get a pdf that shows the
difference at the best alignment between the two images,
at each of the four levels. The red and green pixels
show locations where one image has a fg pixel and the
other doesn't. The black pixels are where both images
have fg pixels, and white pixels are where neither image
has fg pixels.
Definition at line 3420 of file compare.c.
References L_BRING_IN_WHITE, L_CLONE, L_FLATE_ENCODE, L_INSERT, pixBestCorrelation(), and pixDisplayDiffBinary().
| [in] | pix1 | 1 bpp |
| [in] | pix2 | 1 bpp |
| [out] | pval | correlation |
Notes:
(1) The correlation is a number between 0.0 and 1.0,
based on foreground similarity:
(|1 AND 2|)**2
correlation = --------------
|1| * |2|
where |x| is the count of foreground pixels in image x.
If the images are identical, this is 1.0.
If they have no fg pixels in common, this is 0.0.
If one or both images have no fg pixels, the correlation is 0.0.
(2) Typically the two images are of equal size, but this
is not enforced. Instead, the UL corners are aligned.
| l_ok pixCropAlignedToCentroid | ( | PIX * | pix1, |
| PIX * | pix2, | ||
| l_int32 | factor, | ||
| BOX ** | pbox1, | ||
| BOX ** | pbox2 ) |
| [in] | pix1,pix2 | any depth; colormap OK |
| [in] | factor | subsampling; >= 1 |
| [out] | pbox1 | crop box for pix1 |
| [out] | pbox2 | crop box for pix2 |
Notes:
(1) This finds the maximum crop boxes for two 8 bpp images when
their centroids of their photometric inverses are aligned.
Black pixels have weight 255; white pixels have weight 0.
Definition at line 3214 of file compare.c.
References pixCentroid8().
Referenced by pixCompareGrayByHisto().
| l_ok pixDecideIfPhotoImage | ( | PIX * | pix, |
| l_int32 | factor, | ||
| l_float32 | thresh, | ||
| l_int32 | n, | ||
| NUMAA ** | pnaa, | ||
| PIXA * | pixadebug ) |
| [in] | pix | 8 bpp, centroid in center |
| [in] | factor | subsampling for histograms; >= 1 |
| [in] | thresh | threshold for photo/text; use 0 for default |
| [in] | n | in range {1, ... 7}. n^2 is the maximum number of subregions for histograms; typ. n = 3. |
| [out] | pnaa | array of normalized histograms |
| [in] | pixadebug | [optional] use only for debug output |
Notes:
(1) The input image must be 8 bpp (no colormap), and padded with
white pixels so the centroid of photo-inverted pixels is at
the center of the image.
(2) The parameter n specifies the "side" of the n x n grid
of subimages. If the subimages have an aspect ratio larger
than 2, the grid will change, using n^2 as a maximum for
the number of subimages. For example, if n == 3, but the
image is 600 x 200 pixels, a 3x3 grid would have subimages
of 200 x 67 pixels, which is more than 2:1, so we change
to a 4x2 grid where each subimage has 150 x 100 pixels.
(3) If the pix is not almost certainly a photoimage, the returned
histograms (naa) are null.
(4) If histograms are generated, the white (255) count is set
to 0. This removes all pixels values above 230, including
white padding from the centroid matching operation, from
consideration. The resulting histograms are then normalized
so the maximum count is 255.
(5) Default for thresh is 1.3; this seems sufficiently conservative.
(6) Use pixadebug == NULL unless debug output is requested.
Definition at line 2579 of file compare.c.
References findHistoGridDimensions(), L_CLONE, and L_INSERT.
Referenced by pixGenPhotoHistos().
| PIX * pixDisplayDiff | ( | PIX * | pix1, |
| PIX * | pix2, | ||
| l_int32 | showall, | ||
| l_int32 | mindiff, | ||
| l_uint32 | diffcolor ) |
| [in] | pix1 | any depth |
| [in] | pix2 | any depth |
| [in] | showall | 1 to display input images; 0 to only display result |
| [in] | mindiff | min difference to identify pixel |
| [in] | diffcolor | color of pixel indicating difference >= mindiff |
Notes:
(1) This aligns the UL corners of pix1 and pix2, crops to the
overlapping pixels, and shows which pixels have a significant
difference in value.
(2) Requires pix1 and pix2 to have the same depth.
(3) If rgb, a pixel is identified as different if any component
values of the corresponding pixels equals or exceeds mindiff.
(4) diffcolor is in format 0xrrggbbaa.
(5) If pix1 and pix2 are 1 bpp, ignores mindiff and diffcolor,
and uses the result of pixDisplayDiffBinary().
Definition at line 657 of file compare.c.
References GET_DATA_FOUR_BYTES, L_COPY, L_INSERT, PIX_SRC, pixDisplayDiffBinary(), and SET_DATA_FOUR_BYTES.
| [in] | pix1 | 1 bpp |
| [in] | pix2 | 1 bpp |
Notes:
(1) This gives a color representation of the difference between
pix1 and pix2. The color difference depends on the order.
The pixels in pixd have 4 colors:
* unchanged: black (on), white (off)
* on in pix1, off in pix2: red
* on in pix2, off in pix1: green
(2) This aligns the UL corners of pix1 and pix2, and crops
to the overlapping pixels.
Definition at line 753 of file compare.c.
Referenced by pixCompareWithTranslation(), and pixDisplayDiff().
| [in] | pix1 | |
| [in] | pix2 | |
| [out] | psame | 1 if same; 0 if different |
Notes:
(1) Equality is defined as having the same pixel values for
each respective image pixel.
(2) This works on two pix of any depth. If one or both pix
have a colormap, the depths can be different and the
two pix can still be equal.
(3) This ignores the alpha component for 32 bpp images.
(4) If both pix have colormaps and the depths are equal,
use the pixEqualWithCmap() function, which does a fast
comparison if the colormaps are identical and a relatively
slow comparison otherwise.
(5) In all other cases, any existing colormaps must first be
removed before doing pixel comparison. After the colormaps
are removed, the resulting two images must have the same depth.
The "lowest common denominator" is RGB, but this is only
chosen when necessary, or when both have colormaps but
different depths.
(6) For images without colormaps that are not 32 bpp, all bits
in the image part of the data array must be identical.
Definition at line 157 of file compare.c.
References pixEqualWithAlpha().
Referenced by pixGetPSNR().
| [in] | pix1 | |
| [in] | pix2 | |
| [in] | use_alpha | 1 to compare alpha in RGBA; 0 to ignore |
| [out] | psame | 1 if same; 0 if different |
Notes:
(1) See notes in pixEqual().
(2) This is more general than pixEqual(), in that for 32 bpp
RGBA images, where spp = 4, you can optionally include
the alpha component in the comparison.
Definition at line 183 of file compare.c.
References pixEqualWithCmap(), pixUsesCmapColor(), REMOVE_CMAP_TO_FULL_COLOR, and REMOVE_CMAP_TO_GRAYSCALE.
Referenced by pixEqual().
| [in] | pix1 | |
| [in] | pix2 | |
| [out] | psame |
Notes:
(1) This returns same = TRUE if the images have identical content.
(2) Both pix must have a colormap, and be of equal size and depth.
If these conditions are not satisfied, it is not an error;
the returned result is same = FALSE.
(3) We then check whether the colormaps are the same; if so,
the comparison proceeds 32 bits at a time.
(4) If the colormaps are different, the comparison is done by
slow brute force.
Definition at line 383 of file compare.c.
References cmapEqual().
Referenced by pixEqualWithAlpha().
| l_ok pixGenPhotoHistos | ( | PIX * | pixs, |
| BOX * | box, | ||
| l_int32 | factor, | ||
| l_float32 | thresh, | ||
| l_int32 | n, | ||
| NUMAA ** | pnaa, | ||
| l_int32 * | pw, | ||
| l_int32 * | ph, | ||
| l_int32 | debugindex ) |
| [in] | pixs | depth > 1 bpp; colormap OK |
| [in] | box | [optional] region to be selected; can be null |
| [in] | factor | subsampling; >= 1 |
| [in] | thresh | threshold for photo/text; use 0 for default |
| [in] | n | in range {1, ... 7}. n^2 is the maximum number of subregions for histograms; typ. n = 3. |
| [out] | pnaa | nx * ny 256-entry gray histograms |
| [out] | pw | width of image used to make histograms |
| [out] | ph | height of image used to make histograms |
| [in] | debugindex | 0 for no debugging; positive integer otherwise |
Notes:
(1) This crops and converts to 8 bpp if necessary. It adds a
minimal white boundary such that the centroid of the
photo-inverted image is in the center. This allows
automatic alignment with histograms of other image regions.
(2) The parameter n specifies the "side" of the n x n grid
of subimages. If the subimages have an aspect ratio larger
than 2, the grid will change, using n^2 as a maximum for
the number of subimages. For example, if n == 3, but the
image is 600 x 200 pixels, a 3x3 grid would have subimages
of 200 x 67 pixels, which is more than 2:1, so we change
to a 4x2 grid where each subimage has 150 x 100 pixels.
(3) The white value in the histogram is removed, because of
the padding.
(4) Use 0 for conservative default (1.3) for thresh.
(5) For an efficient representation of the histogram, normalize
using a multiplicative factor so that the number in the
maximum bucket is 255. It then takes 256 bytes to store.
(6) With debugindex > 0, this makes a pdf that shows, for each tile,
the images and histograms.
Definition at line 2332 of file compare.c.
References L_FLATE_ENCODE, L_INSERT, pixDecideIfPhotoImage(), and pixPadToCenterCentroid().
Referenced by pixaComparePhotoRegionsByHisto(), and pixComparePhotoRegionsByHisto().
| [in] | pix1 | 8 bpp gray or 32 bpp rgb, or colormapped |
| [in] | pix2 | 8 bpp gray or 32 bpp rgb, or colormapped |
| [in] | factor | subsampling factor; use 0 or 1 for no subsampling |
Notes:
(1) The two images are aligned at the UL corner, and do not
need to be the same size. If they are not the same size,
the comparison will be made over overlapping pixels.
(2) If there is a colormap, it is removed and the result
is either gray or RGB depending on the colormap.
(3) If RGB, the maximum difference between pixel components is
saved in the histogram.
Definition at line 1580 of file compare.c.
References GET_DATA_BYTE, L_NOCOPY, and REMOVE_CMAP_BASED_ON_SRC.
Referenced by pixCompareRankDifference(), and pixGetDifferenceStats().
| l_ok pixGetDifferenceStats | ( | PIX * | pix1, |
| PIX * | pix2, | ||
| l_int32 | factor, | ||
| l_int32 | mindiff, | ||
| l_float32 * | pfractdiff, | ||
| l_float32 * | pavediff, | ||
| l_int32 | details ) |
| [in] | pix1 | 8 bpp gray or 32 bpp rgb, or colormapped |
| [in] | pix2 | 8 bpp gray or 32 bpp rgb, or colormapped |
| [in] | factor | subsampling factor; use 0 or 1 for no subsampling |
| [in] | mindiff | minimum pixel difference to be counted; > 0 |
| [out] | pfractdiff | fraction of pixels with diff greater than or equal to mindiff |
| [out] | pavediff | average difference of pixels with diff greater than or equal to mindiff, less mindiff |
| [in] | details | use 1 to give normalized histogram and other data |
Notes:
(1) This takes a threshold mindiff and describes the difference
between two images in terms of two numbers:
(a) the fraction of pixels, fractdiff, whose difference
equals or exceeds the threshold mindiff, and
(b) the average value avediff of the difference in pixel value
for the pixels in the set given by (a), after you subtract
mindiff. The reason for subtracting mindiff is that
you then get a useful measure for the rate of falloff
of the distribution for larger differences. For example,
if mindiff = 10 and you find that avediff = 2.5, it
says that of the pixels with diff > 10, the average of
their diffs is just mindiff + 2.5 = 12.5. This is a
fast falloff in the histogram with increasing difference.
(2) The two images are aligned at the UL corner, and do not
need to be the same size. If they are not the same size,
the comparison will be made over overlapping pixels.
(3) If there is a colormap, it is removed and the result
is either gray or RGB depending on the colormap.
(4) If RGB, the maximum difference between pixel components is
saved in the histogram.
(5) Set details == 1 to see the difference histogram and get
an output that shows for each value of mindiff, what are the
minimum values required for fractdiff and avediff in order
that the two pix will be considered similar.
Definition at line 1480 of file compare.c.
References L_NOCOPY, and pixGetDifferenceHistogram().
Referenced by pixTestForSimilarity().
| l_ok pixGetPerceptualDiff | ( | PIX * | pixs1, |
| PIX * | pixs2, | ||
| l_int32 | sampling, | ||
| l_int32 | dilation, | ||
| l_int32 | mindiff, | ||
| l_float32 * | pfract, | ||
| PIX ** | ppixdiff1, | ||
| PIX ** | ppixdiff2 ) |
| [in] | pixs1 | 8 bpp gray or 32 bpp rgb, or colormapped |
| [in] | pixs2 | 8 bpp gray or 32 bpp rgb, or colormapped |
| [in] | sampling | subsampling factor; use 0 or 1 for no subsampling |
| [in] | dilation | size of grayscale or color Sel; odd |
| [in] | mindiff | minimum pixel difference to be counted; > 0 |
| [out] | pfract | fraction of pixels with diff greater than mindiff |
| [out] | ppixdiff1 | [optional] showing difference (gray or color) |
| [out] | ppixdiff2 | [optional] showing pixels of sufficient diff |
Notes:
(1) This takes 2 pix and determines, using 2 input parameters:
* dilation specifies the amount of grayscale or color
dilation to apply to the images, to compensate for
a small amount of misregistration. A typical number might
be 5, which uses a 5x5 Sel. Grayscale dilation expands
lighter pixels into darker pixel regions.
* mindiff determines the threshold on the difference in
pixel values to be counted -- two pixels are not similar
if their difference in value is at least mindiff. For
color pixels, we use the maximum component difference.
(2) The pixelwise comparison is always done with the UL corners
aligned. The sizes of pix1 and pix2 need not be the same,
although in practice it can be useful to scale to the same size.
(3) If there is a colormap, it is removed and the result
is either gray or RGB depending on the colormap.
(4) Two optional diff images can be retrieved (typ. for debugging):
pixdiff1: the gray or color difference
pixdiff2: thresholded to 1 bpp for pixels exceeding mindiff
(5) The returned value of fract can be compared to some threshold,
which is application dependent.
(6) This method is in analogy to the two-sided hausdorff transform,
except here it is for d > 1. For d == 1 (see pixRankHaustest()),
we verify that when one pix1 is dilated, it covers at least a
given fraction of the pixels in pix2, and v.v.; in that
case, the two pix are sufficiently similar. Here, we
do an analogous thing: subtract the dilated pix1 from pix2 to
get a 1-sided hausdorff-like transform. Then do it the
other way. Take the component-wise max of the two results,
and threshold to get the fraction of pixels with a difference
below the threshold.
Definition at line 1709 of file compare.c.
References pixCompareGray(), pixCompareRGB(), and REMOVE_CMAP_BASED_ON_SRC.
| [in] | pix1,pix2 | 8 or 32 bpp; no colormap |
| [in] | factor | sampling factor; >= 1 |
| [out] | ppsnr | power signal/noise ratio difference |
Notes:
(1) This computes the power S/N ratio, in dB, for the difference
between two images. By convention, the power S/N
for a grayscale image is ('log' == log base 10,
and 'ln == log base e):
PSNR = 10 * log((255/MSE)^2)
= 4.3429 * ln((255/MSE)^2)
= -4.3429 * ln((MSE/255)^2)
where MSE is the mean squared error.
Here are some examples:
MSE PSNR
--- ----
10 28.1
3 38.6
1 48.1
0.1 68.1
(2) If pix1 and pix2 have the same pixel values, the MSE = 0.0
and the PSNR is infinity. For that case, this returns
PSNR = 1000, which corresponds to the very small MSE of
about 10^(-48).
Definition at line 1874 of file compare.c.
References GET_DATA_BYTE, and pixEqual().
| [in] | pixs | any depth, colormap OK |
| [in] | factor | subsampling for centroid; >= 1 |
Notes:
(1) This add minimum white padding to an 8 bpp pix, such that
the centroid of the photometric inverse is in the center of
the resulting image. Thus in computing the centroid,
black pixels have weight 255, and white pixels have weight 0.
Definition at line 2443 of file compare.c.
References PIX_SRC, and pixCentroid8().
Referenced by pixGenPhotoHistos().
| l_ok pixTestForSimilarity | ( | PIX * | pix1, |
| PIX * | pix2, | ||
| l_int32 | factor, | ||
| l_int32 | mindiff, | ||
| l_float32 | maxfract, | ||
| l_float32 | maxave, | ||
| l_int32 * | psimilar, | ||
| l_int32 | details ) |
| [in] | pix1 | 8 bpp gray or 32 bpp rgb, or colormapped |
| [in] | pix2 | 8 bpp gray or 32 bpp rgb, or colormapped |
| [in] | factor | subsampling factor; use 0 or 1 for no subsampling |
| [in] | mindiff | minimum pixel difference to be counted; > 0 |
| [in] | maxfract | maximum fraction of pixels allowed to have diff greater than or equal to mindiff |
| [in] | maxave | maximum average difference of pixels allowed for pixels with diff greater than or equal to mindiff, after subtracting mindiff |
| [out] | psimilar | 1 if similar, 0 otherwise |
| [in] | details | use 1 to give normalized histogram and other data |
Notes:
(1) This takes 2 pix that are the same size and determines using
3 input parameters if they are "similar". The first parameter
mindiff establishes a criterion of pixel-to-pixel similarity:
two pixels are not similar if their difference in value is
at least mindiff. Then maxfract and maxave are thresholds
on the number and distribution of dissimilar pixels
allowed for the two pix to be similar. If the pix are
to be similar, neither threshold can be exceeded.
(2) In setting the maxfract and maxave thresholds, you have
these options:
(a) Base the comparison only on maxfract. Then set
maxave = 0.0 or 256.0. (If 0, we always ignore it.)
(b) Base the comparison only on maxave. Then set
maxfract = 1.0.
(c) Base the comparison on both thresholds.
(3) Example of values that can be expected at mindiff = 15 when
comparing lossless png encoding with jpeg encoding, q=75:
(smoothish bg) fractdiff = 0.01, avediff = 2.5
(natural scene) fractdiff = 0.13, avediff = 3.5
To identify these images as 'similar', select maxfract
and maxave to be upper bounds of what you expect.
(4) See pixGetDifferenceStats() for a discussion of why we subtract
mindiff from the computed average diff of the nonsimilar pixels
to get the 'avediff' returned by that function.
(5) If there is a colormap, it is removed and the result
is either gray or RGB depending on the colormap.
(6) If RGB, the maximum difference between pixel components is
saved in the histogram.
Definition at line 1403 of file compare.c.
References pixGetDifferenceStats().
| l_ok pixUsesCmapColor | ( | PIX * | pixs, |
| l_int32 * | pcolor ) |
| [in] | pixs | any depth, colormap |
| [out] | pcolor | TRUE if color found |
Notes:
(1) This returns color = TRUE if three things are obtained:
(a) the pix has a colormap
(b) the colormap has at least one color entry
(c) a color entry is actually used
(2) It is used in pixEqual() for comparing two images, in a
situation where it is required to know if the colormap
has color entries that are actually used in the image.
Definition at line 533 of file compare.c.
Referenced by pixEqualWithAlpha().
1.12.0