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bayer2rgb: Add comments explaining gst_bayer2rgb_process()
Add comments regarding which LINE()s point to which data in the temporary buffer and a large comment explaining how the buffer is processed. This will hopefully be useful to someone, as the code is not obvious. No functional change. Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/4686>
This commit is contained in:
Marek Vasut
parent
920851945f
commit
9d1a750117
1 changed files with 70 additions and 0 deletions
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@ -483,11 +483,13 @@ gst_bayer2rgb_process (GstBayer2RGB * bayer2rgb, uint8_t * dest,
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tmp = g_malloc (2 * 4 * bayer2rgb->width);
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#define LINE(t, x, b) ((t) + (((x) & 7) * ((b)->width)))
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/* Pre-process source line 1 into bottom two lines 6 and 7 as PREVIOUS line */
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gst_bayer2rgb_split_and_upsample_horiz ( /* src line 1 */
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LINE (tmp, 3 * 2 + 0, bayer2rgb), /* tmp buffer line 6 */
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LINE (tmp, 3 * 2 + 1, bayer2rgb), /* tmp buffer line 7 */
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src + 1 * src_stride, bayer2rgb);
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/* Pre-process source line 0 into top two lines 0 and 1 as CURRENT line */
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gst_bayer2rgb_split_and_upsample_horiz ( /* src line 0 */
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LINE (tmp, 0 * 2 + 0, bayer2rgb), /* tmp buffer line 0 */
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LINE (tmp, 0 * 2 + 1, bayer2rgb), /* tmp buffer line 1 */
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@ -495,12 +497,80 @@ gst_bayer2rgb_process (GstBayer2RGB * bayer2rgb, uint8_t * dest,
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for (j = 0; j < bayer2rgb->height; j++) {
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if (j < bayer2rgb->height - 1) {
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/*
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* Pre-process NEXT source line (j + 1) into two consecutive lines
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* (2 * (j + 1) + 0) % 8
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* and
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* (2 * (j + 1) + 1) % 8
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*
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* This cycle here starts with j=0, and therefore
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* - reads source line 1
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* - writes tmp buffer lines 2,3
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* The cycle continues with source line 2 and tmp buffer lines 4,5 etc.
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*/
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gst_bayer2rgb_split_and_upsample_horiz ( /* src line (j + 1) */
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LINE (tmp, (j + 1) * 2 + 0, bayer2rgb), /* tmp buffer line 2/4/6/0 */
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LINE (tmp, (j + 1) * 2 + 1, bayer2rgb), /* tmp buffer line 3/5/7/1 */
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src + (j + 1) * src_stride, bayer2rgb);
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}
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/*
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* Use the pre-processed tmp buffer lines and construct resulting frame.
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* Assume j=0, the tmp buffer content looks as follows:
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* line 0: B0 avg(B0, B1) B1 avg(B1, B2) B2 avg(B2, B3)...
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* line 1: G0 G0 avg(G0, G1) G1 avg(G1, G2) G2...
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* line 2: G0 avg(G0, G1) G1 avg(G1, G2) G2 avg(G2, G3)...
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* line 3: R0 R0 avg(R0, R1) R1 avg(R1, R2) R2...
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* line 4: empty
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* line 5: empty
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* line 6: G0 avg(G0, G1) G1 avg(G1, G2) G2 avg(G2, G3)...
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* line 7: R0 R0 avg(R0, R1) R1 avg(R1, R2) R2...
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* Line 0,1 and 6,7 were populated in pre-process step outside of this loop.
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* Line 2,3 was populated just above this comment.
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* The code is currently processing source line 0 (not tmp buffer line 0)
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* and uses the following tmp buffer lines in the process as inputs to the
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* merge function:
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* - tmp buffer line -2 => tmp buffer line 6 => orc g0 values
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* - tmp buffer line -1 => tmp buffer line 7 => orc r0 values
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* - tmp buffer line +0 => tmp buffer line 0 => orc b1 values
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* - tmp buffer line +1 => tmp buffer line 1 => orc g1 values
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* - tmp buffer line +2 => tmp buffer line 2 => orc g2 values
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* - tmp buffer line +3 => tmp buffer line 3 => orc r2 values
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* With j=0, the merge function used is one of bayer_orc_merge_bg_*
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*
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* A good material regarding the ORC functions below is
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* https://www.siliconimaging.com/RGB%20Bayer.htm
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* chapter
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* "Interpolating the green component"
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*
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* The bayer_orc_merge_bg_* performs BG interpolation.
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* # average R from PREVIOUS line and NEXT line
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* r = [ avg(r0[0], r2[0]) , avg(r0[1], r2[1]) ]
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* # average G from PREVIOUS line and NEXT line
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* g = [ avg(g0[0], g2[0]) , avg(g0[1], g2[1]) ]
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* # copy CURRENT line G into variable t
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* t = [ g1[0] , g1[1] ]
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* # average G from PREVIOUS, CURRENT, NEXT line
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* g = [ avg(g[0], g1[0]) , avg(g[1], g1[1]) ]
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* # reorder the content of g and t variables using bit operations
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* # (the "g first, t second" order is here because the B pixel we
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* # are now processing does not have its own G value, it only has
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* # G value extrapolated from surrouding G pixels. The following
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* # G pixel has its own G value, so we use it as-is, without any
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* # extrapolation)
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* g = [ g, 0 ]
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* t = [ 0, t ]
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* g = [ g, t ]
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* # generate resulting (e.g. BGRx) data
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* bg = [ b1[0] , g , b1[1] , t ]
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* ra = [ r[0] , 255 , r[1] , 255 ]
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* d = [ b1[0] , g , r[0] , 255 , b1[1] , t , r[1] , 255 ]
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*
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* In the next cycle, j=1, line 4,5 would be populated with BG values
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* calculated from source line 2, merge function would use tmp buffer
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* inputs from lines 0,1,2,3,4,5 i.e. b0,g0,g1,r1,b2,g2 and the merge
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* function would be bayer_orc_merge_gr_* .
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*/
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merge[j & 1] (dest + j * dest_stride, /* output line j */
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LINE (tmp, j * 2 - 2, bayer2rgb), /* PREVIOUS: even: BG g0 , odd: GR b0 */
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LINE (tmp, j * 2 - 1, bayer2rgb), /* PREVIOUS: even: BG r0 , odd: GR g0 */
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