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TurboJPEG: Decompress 4:4:4 JPEGs with unusual SFs

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Normally, 4:4:4 JPEGs have horizontal x vertical luminance & chrominance
sampling factors of 1x1.  However, it is technically legal to create
4:4:4 JPEGs with sampling factors of 2x1, 1x2, 3x1, or 1x3, since the
sums of the products of those sampling factors are still <= 10.  The
libjpeg API correctly decodes such images, so the TurboJPEG API should
as well.

Fixes #323
This commit is contained in:
DRC
2019-01-21 13:57:55 -06:00
parent 9bc8eb6449
commit 479501b07c
2 changed files with 23 additions and 0 deletions
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6
ChangeLog.md
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@@ -22,6 +22,12 @@ djpeg.
decompress a specially-crafted malformed JPEG image with a specified image decompress a specially-crafted malformed JPEG image with a specified image
width or height of 0 using the C version of TJBench. width or height of 0 using the C version of TJBench.
5. The TurboJPEG API will now decompress 4:4:4 JPEG images with 2x1, 1x2, 3x1,
or 1x3 luminance and chrominance sampling factors. This is a non-standard way
of specifying 1x subsampling (normally 4:4:4 JPEGs have 1x1 luminance and
chrominance sampling factors), but the JPEG format and the libjpeg API both
allow it.
2.0.1 2.0.1
===== =====

17
turbojpeg.c
View File

@@ -359,6 +359,23 @@ static int getSubsamp(j_decompress_ptr dinfo)
retval = i; break; retval = i; break;
} }
} }
/* Handle 4:4:4 images whose sampling factors are specified in
non-standard ways. */
if (dinfo->comp_info[0].h_samp_factor *
dinfo->comp_info[0].v_samp_factor <=
D_MAX_BLOCKS_IN_MCU / pixelsize[i] && i == TJSAMP_444) {
int match = 0;
for (k = 1; k < dinfo->num_components; k++) {
if (dinfo->comp_info[i].h_samp_factor ==
dinfo->comp_info[0].h_samp_factor &&
dinfo->comp_info[i].v_samp_factor ==
dinfo->comp_info[0].v_samp_factor)
match++;
if (match == dinfo->num_components - 1) {
retval = i; break;
}
}
}
} }
} }
return retval; return retval;