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Implement h1v2 fancy upsampling

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This allows fancy upsampling to be used when decompressing 4:2:2 images
that have been losslessly rotated or transposed.

(docs and comments added by DRC)

Based on f63aca945d

Closes #89
This commit is contained in:
Kornel Lesiński
2016-07-10 19:01:51 +01:00
committed by DRC
parent 1120ff29a1
commit 628c168c86
2 changed files with 52 additions and 0 deletions
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47
jdsample.c
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@@ -303,6 +303,48 @@ h2v1_fancy_upsample (j_decompress_ptr cinfo, jpeg_component_info *compptr,
}
/*
* Fancy processing for 1:1 horizontal and 2:1 vertical (4:4:0 subsampling).
*
* This is a less common case, but it can be encountered when losslessly
* rotating/transposing a JPEG file that uses 4:2:2 chroma subsampling.
*/
METHODDEF(void)
h1v2_fancy_upsample (j_decompress_ptr cinfo, jpeg_component_info *compptr,
JSAMPARRAY input_data, JSAMPARRAY *output_data_ptr)
{
JSAMPARRAY output_data = *output_data_ptr;
JSAMPROW inptr0, inptr1, outptr;
#if BITS_IN_JSAMPLE == 8
int thiscolsum;
#else
JLONG thiscolsum;
#endif
JDIMENSION colctr;
int inrow, outrow, v;
inrow = outrow = 0;
while (outrow < cinfo->max_v_samp_factor) {
for (v = 0; v < 2; v++) {
/* inptr0 points to nearest input row, inptr1 points to next nearest */
inptr0 = input_data[inrow];
if (v == 0) /* next nearest is row above */
inptr1 = input_data[inrow-1];
else /* next nearest is row below */
inptr1 = input_data[inrow+1];
outptr = output_data[outrow++];
for(colctr = 0; colctr < compptr->downsampled_width; colctr++) {
thiscolsum = GETJSAMPLE(*inptr0++) * 3 + GETJSAMPLE(*inptr1++);
*outptr++ = (JSAMPLE) ((thiscolsum + 1) >> 2);
}
}
inrow++;
}
}
/*
* Fancy processing for the common case of 2:1 horizontal and 2:1 vertical.
* Again a triangle filter; see comments for h2v1 case, above.
@@ -431,6 +473,11 @@ jinit_upsampler (j_decompress_ptr cinfo)
else
upsample->methods[ci] = h2v1_upsample;
}
} else if (h_in_group == h_out_group &&
v_in_group * 2 == v_out_group && do_fancy) {
/* Non-fancy upsampling is handled by the generic method */
upsample->methods[ci] = h1v2_fancy_upsample;
upsample->pub.need_context_rows = TRUE;
} else if (h_in_group * 2 == h_out_group &&
v_in_group * 2 == v_out_group) {
/* Special cases for 2h2v upsampling */