diff mbox series

[FFmpeg-devel] webp: fix transforms after a palette with pixel packing.

Message ID 20210819075609.20021-1-maryla@google.com
State New
Headers show
Series [FFmpeg-devel] webp: fix transforms after a palette with pixel packing.
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Commit Message

Maryla Aug. 19, 2021, 7:56 a.m. UTC
When a color indexing transform with 16 or fewer colors is used,
WebP uses "pixel packing", i.e. storing several pixels in one byte,
which virtually reduces the width of the image (see WebPContext's
reduced_width field). This reduced_width should always be used when
reading and applying subsequent transforms.

Fixes: 9368
---
 libavcodec/webp.c | 34 ++++++++++++++++++----------------
 1 file changed, 18 insertions(+), 16 deletions(-)

Comments

James Zern Aug. 20, 2021, 5:06 p.m. UTC | #1
On Thu, Aug 19, 2021 at 12:56 AM Maryla <maryla-at-google.com@ffmpeg.org> wrote:
>
> When a color indexing transform with 16 or fewer colors is used,
> WebP uses "pixel packing", i.e. storing several pixels in one byte,
> which virtually reduces the width of the image (see WebPContext's
> reduced_width field). This reduced_width should always be used when
> reading and applying subsequent transforms.
>
> Fixes: 9368

Is there anything in
https://chromium.googlesource.com/webm/libwebp-test-data that covers
this or can you add the file from the ticket to fate?
Maryla Aug. 26, 2021, 4:06 p.m. UTC | #2
We've just added a file to libwebp-test-data that covers this case:
https://chromium.googlesource.com/webm/libwebp-test-data/+/refs/heads/main/dual_transform.webp
FFmpeg currently fails to decode it, but it works with this patch.

My understanding is that an ffmpeg developer needs to upload the file to
fate, and then I can add a fate test to the patch?



On Fri, Aug 20, 2021 at 7:07 PM James Zern <jzern-at-google.com@ffmpeg.org>
wrote:

> On Thu, Aug 19, 2021 at 12:56 AM Maryla <maryla-at-google.com@ffmpeg.org>
> wrote:
> >
> > When a color indexing transform with 16 or fewer colors is used,
> > WebP uses "pixel packing", i.e. storing several pixels in one byte,
> > which virtually reduces the width of the image (see WebPContext's
> > reduced_width field). This reduced_width should always be used when
> > reading and applying subsequent transforms.
> >
> > Fixes: 9368
>
> Is there anything in
> https://chromium.googlesource.com/webm/libwebp-test-data that covers
> this or can you add the file from the ticket to fate?
> _______________________________________________
> ffmpeg-devel mailing list
> ffmpeg-devel@ffmpeg.org
> https://ffmpeg.org/mailman/listinfo/ffmpeg-devel
>
> To unsubscribe, visit link above, or email
> ffmpeg-devel-request@ffmpeg.org with subject "unsubscribe".
>
James Zern Aug. 26, 2021, 11:50 p.m. UTC | #3
Hi,

On Thu, Aug 26, 2021 at 9:06 AM Maryla Ustarroz
<maryla-at-google.com@ffmpeg.org> wrote:
>

Note top posting is discouraged here [1].

> We've just added a file to libwebp-test-data that covers this case:
> https://chromium.googlesource.com/webm/libwebp-test-data/+/refs/heads/main/dual_transform.webp
> FFmpeg currently fails to decode it, but it works with this patch.
>
> My understanding is that an ffmpeg developer needs to upload the file to
> fate, and then I can add a fate test to the patch?
>

Yes, a link to the file is all that's needed [2][3]. You may include
this as a reply to the initial patch or in the commit message for
visibility.

[1] https://ffmpeg.org/contact.html#MailingLists
[2] https://ffmpeg.org/developer.html#Adding-files-to-the-fate_002dsuite-dataset
[3] https://ffmpeg.org/fate.html#Uploading-new-samples-to-the-fate-suite

>
>
> On Fri, Aug 20, 2021 at 7:07 PM James Zern <jzern-at-google.com@ffmpeg.org>
> wrote:
>
> > On Thu, Aug 19, 2021 at 12:56 AM Maryla <maryla-at-google.com@ffmpeg.org>
> > wrote:
> > >
> > > When a color indexing transform with 16 or fewer colors is used,
> > > WebP uses "pixel packing", i.e. storing several pixels in one byte,
> > > which virtually reduces the width of the image (see WebPContext's
> > > reduced_width field). This reduced_width should always be used when
> > > reading and applying subsequent transforms.
> > >
> > > Fixes: 9368
> >
> > Is there anything in
> > https://chromium.googlesource.com/webm/libwebp-test-data that covers
> > this or can you add the file from the ticket to fate?
> > _______________________________________________
> > ffmpeg-devel mailing list
> > ffmpeg-devel@ffmpeg.org
> > https://ffmpeg.org/mailman/listinfo/ffmpeg-devel
> >
> > To unsubscribe, visit link above, or email
> > ffmpeg-devel-request@ffmpeg.org with subject "unsubscribe".
> >
> _______________________________________________
> ffmpeg-devel mailing list
> ffmpeg-devel@ffmpeg.org
> https://ffmpeg.org/mailman/listinfo/ffmpeg-devel
>
> To unsubscribe, visit link above, or email
> ffmpeg-devel-request@ffmpeg.org with subject "unsubscribe".
diff mbox series

Patch

diff --git a/libavcodec/webp.c b/libavcodec/webp.c
index 83371ef6fd..52e5a4f65a 100644
--- a/libavcodec/webp.c
+++ b/libavcodec/webp.c
@@ -181,7 +181,10 @@  typedef struct ImageContext {
     uint32_t *color_cache;              /* color cache data */
     int nb_huffman_groups;              /* number of huffman groups */
     HuffReader *huffman_groups;         /* reader for each huffman group */
-    int size_reduction;                 /* relative size compared to primary image, log2 */
+    /* relative size compared to primary image, log2.
+     * for IMAGE_ROLE_COLOR_INDEXING with <= 16 colors, this is log2 of the
+     * number of pixels per byte in the primary image (pixel packing) */
+    int size_reduction;
     int is_alpha_primary;
 } ImageContext;
 
@@ -205,7 +208,9 @@  typedef struct WebPContext {
 
     int nb_transforms;                  /* number of transforms */
     enum TransformType transforms[4];   /* transformations used in the image, in order */
-    int reduced_width;                  /* reduced width for index image, if applicable */
+    /* reduced width when using a color indexing transform with <= 16 colors (pixel packing)
+     * before pixels are unpacked, or same as width otherwise. */
+    int reduced_width;
     int nb_huffman_groups;              /* number of huffman groups in the primary image */
     ImageContext image[IMAGE_ROLE_NB];  /* image context for each role */
 } WebPContext;
@@ -425,13 +430,9 @@  static int decode_entropy_coded_image(WebPContext *s, enum ImageRole role,
 static int decode_entropy_image(WebPContext *s)
 {
     ImageContext *img;
-    int ret, block_bits, width, blocks_w, blocks_h, x, y, max;
+    int ret, block_bits, blocks_w, blocks_h, x, y, max;
 
-    width = s->width;
-    if (s->reduced_width > 0)
-        width = s->reduced_width;
-
-    PARSE_BLOCK_SIZE(width, s->height);
+    PARSE_BLOCK_SIZE(s->reduced_width, s->height);
 
     ret = decode_entropy_coded_image(s, IMAGE_ROLE_ENTROPY, blocks_w, blocks_h);
     if (ret < 0)
@@ -460,7 +461,7 @@  static int parse_transform_predictor(WebPContext *s)
 {
     int block_bits, blocks_w, blocks_h, ret;
 
-    PARSE_BLOCK_SIZE(s->width, s->height);
+    PARSE_BLOCK_SIZE(s->reduced_width, s->height);
 
     ret = decode_entropy_coded_image(s, IMAGE_ROLE_PREDICTOR, blocks_w,
                                      blocks_h);
@@ -476,7 +477,7 @@  static int parse_transform_color(WebPContext *s)
 {
     int block_bits, blocks_w, blocks_h, ret;
 
-    PARSE_BLOCK_SIZE(s->width, s->height);
+    PARSE_BLOCK_SIZE(s->reduced_width, s->height);
 
     ret = decode_entropy_coded_image(s, IMAGE_ROLE_COLOR_TRANSFORM, blocks_w,
                                      blocks_h);
@@ -620,7 +621,7 @@  static int decode_entropy_coded_image(WebPContext *s, enum ImageRole role,
     }
 
     width = img->frame->width;
-    if (role == IMAGE_ROLE_ARGB && s->reduced_width > 0)
+    if (role == IMAGE_ROLE_ARGB)
         width = s->reduced_width;
 
     x = 0; y = 0;
@@ -922,7 +923,7 @@  static int apply_predictor_transform(WebPContext *s)
     int x, y;
 
     for (y = 0; y < img->frame->height; y++) {
-        for (x = 0; x < img->frame->width; x++) {
+        for (x = 0; x < s->reduced_width; x++) {
             int tx = x >> pimg->size_reduction;
             int ty = y >> pimg->size_reduction;
             enum PredictionMode m = GET_PIXEL_COMP(pimg->frame, tx, ty, 2);
@@ -962,7 +963,7 @@  static int apply_color_transform(WebPContext *s)
     cimg = &s->image[IMAGE_ROLE_COLOR_TRANSFORM];
 
     for (y = 0; y < img->frame->height; y++) {
-        for (x = 0; x < img->frame->width; x++) {
+        for (x = 0; x < s->reduced_width; x++) {
             cx = x >> cimg->size_reduction;
             cy = y >> cimg->size_reduction;
             cp = GET_PIXEL(cimg->frame, cx, cy);
@@ -982,7 +983,7 @@  static int apply_subtract_green_transform(WebPContext *s)
     ImageContext *img = &s->image[IMAGE_ROLE_ARGB];
 
     for (y = 0; y < img->frame->height; y++) {
-        for (x = 0; x < img->frame->width; x++) {
+        for (x = 0; x < s->reduced_width; x++) {
             uint8_t *p = GET_PIXEL(img->frame, x, y);
             p[1] += p[2];
             p[3] += p[2];
@@ -1001,7 +1002,7 @@  static int apply_color_indexing_transform(WebPContext *s)
     img = &s->image[IMAGE_ROLE_ARGB];
     pal = &s->image[IMAGE_ROLE_COLOR_INDEXING];
 
-    if (pal->size_reduction > 0) {
+    if (pal->size_reduction > 0) { // undo pixel packing
         GetBitContext gb_g;
         uint8_t *line;
         int pixel_bits = 8 >> pal->size_reduction;
@@ -1027,6 +1028,7 @@  static int apply_color_indexing_transform(WebPContext *s)
             }
         }
         av_free(line);
+        s->reduced_width = s->width; // we are back to full size
     }
 
     // switch to local palette if it's worth initializing it
@@ -1123,7 +1125,7 @@  static int vp8_lossless_decode_frame(AVCodecContext *avctx, AVFrame *p,
 
     /* parse transformations */
     s->nb_transforms = 0;
-    s->reduced_width = 0;
+    s->reduced_width = s->width;
     used = 0;
     while (get_bits1(&s->gb)) {
         enum TransformType transform = get_bits(&s->gb, 2);