[FFmpeg-devel] [PATCH]Fix 1bpp palettized png with width not a multiple of 8

[Carl Eugen Hoyos]

On Tuesday 29 January 2013 03:23:12 pm Michael Niedermayer wrote:
> > +++ b/libavcodec/pngdec.c
> > @@ -768,7 +768,15 @@ static int decode_frame(AVCodecContext *avctx,
> >          int i, j;
> >          uint8_t *pd = s->current_picture->data[0];
> >          for (j = 0; j < s->height; j++) {
> > +            i = s->width / 8;
> > +            if ((s->width&7) >= 7) pd[8*i + 6] = (pd[i]>>1) & 1;
> > +            if ((s->width&7) >= 6) pd[8*i + 5] = (pd[i]>>2) & 1;
> > +            if ((s->width&7) >= 5) pd[8*i + 4] = (pd[i]>>3) & 1;
> > +            if ((s->width&7) >= 4) pd[8*i + 3] = (pd[i]>>4) & 1;
> > +            if ((s->width&7) >= 3) pd[8*i + 2] = (pd[i]>>5) & 1;
> > +            if ((s->width&7) >= 2) pd[8*i + 1] = (pd[i]>>6) & 1;
> > +            if ((s->width&7) >= 1) pd[8*i + 0] =  pd[i]>>7;
>
> should be ok if it works
> alternatively this maybe could be simplified with a loop

New patch attached.

Please review, Carl Eugen
-------------- next part --------------
diff --git a/libavcodec/pngdec.c b/libavcodec/pngdec.c
index 593df60..97c0ad1 100644
--- a/libavcodec/pngdec.c
+++ b/libavcodec/pngdec.c
@@ -765,10 +765,14 @@ static int decode_frame(AVCodecContext *avctx,
  exit_loop:
 
     if (s->bits_per_pixel == 1 && s->color_type == PNG_COLOR_TYPE_PALETTE){
-        int i, j;
+        int i, j, k;
         uint8_t *pd = s->current_picture->data[0];
         for (j = 0; j < s->height; j++) {
-            for (i = s->width/8-1; i >= 0; i--) {
+            i = s->width / 8;
+            for (k = 7; k >= 1; k--)
+                if ((s->width&7) >= k)
+                    pd[8*i + k - 1] = (pd[i]>>8-k) & 1;
+            for (i--; i >= 0; i--) {
                 pd[8*i + 7]=  pd[i]     & 1;
                 pd[8*i + 6]= (pd[i]>>1) & 1;
                 pd[8*i + 5]= (pd[i]>>2) & 1;