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jpeg_crop_scanlines: Handle gray images w/ samp!=1

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Since the sampling factor has no meaning for single-component images,
the decompressor ignores it, and jpeg_crop_scanlines() should as well.

Fixes #195
This commit is contained in:
DRC
2017-12-06 11:59:04 -06:00
parent 773040f9d9
commit c308d43416
2 changed files with 13 additions and 4 deletions
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4
ChangeLog.md
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@@ -37,6 +37,10 @@ end of a single-scan (non-progressive) image, subsequent calls to
`jpeg_consume_input()` would return `JPEG_SUSPENDED` rather than
`JPEG_REACHED_EOI`.
9. `jpeg_crop_scanlines()` now works correctly when decompressing grayscale
JPEG images that were compressed with a sampling factor other than 1 (for
instance, with `cjpeg -grayscale -sample 2x2`).
1.5.2
=====

13
jdapistd.c
View File

@@ -190,7 +190,10 @@ jpeg_crop_scanline (j_decompress_ptr cinfo, JDIMENSION *xoffset,
* single-pass decompression case, allowing us to use the same MCU column
* width for all of the components.
*/
align = cinfo->_min_DCT_scaled_size * cinfo->max_h_samp_factor;
if (cinfo->comps_in_scan == 1 && cinfo->num_components == 1)
align = cinfo->_min_DCT_scaled_size;
else
align = cinfo->_min_DCT_scaled_size * cinfo->max_h_samp_factor;
/* Adjust xoffset to the nearest iMCU boundary <= the requested value */
input_xoffset = *xoffset;
@@ -215,6 +218,9 @@ jpeg_crop_scanline (j_decompress_ptr cinfo, JDIMENSION *xoffset,
for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
ci++, compptr++) {
int hsf = (cinfo->comps_in_scan == 1 && cinfo->num_components == 1) ?
1 : compptr->h_samp_factor;
/* Set downsampled_width to the new output width. */
orig_downsampled_width = compptr->downsampled_width;
compptr->downsampled_width =
@@ -228,11 +234,10 @@ jpeg_crop_scanline (j_decompress_ptr cinfo, JDIMENSION *xoffset,
* values will be used in multi-scan decompressions.
*/
cinfo->master->first_MCU_col[ci] =
(JDIMENSION) (long) (*xoffset * compptr->h_samp_factor) /
(long) align;
(JDIMENSION) (long) (*xoffset * hsf) / (long) align;
cinfo->master->last_MCU_col[ci] =
(JDIMENSION) jdiv_round_up((long) ((*xoffset + cinfo->output_width) *
compptr->h_samp_factor),
hsf),
(long) align) - 1;
}