ref: 6e30d23ceb6a4f999a9c92784a95d27627e9df10
parent: 5efe85a961d95f1b7935fe830933c84b5bf7c7b3
author: Ori Bernstein <ori@eigenstate.org>
date: Sun Jan 11 19:36:56 EST 2026
jpg: fix progressive jpegs with chroma subsampling First, when decoding the DC components, for scans where Ns=1, we need to handle them in raster order, not MCU order[1]. The change to progressivedc() handles the Nf==1 case to deal with the different scan order. Seocnd, need to have all frame components present in the scan, and we needed to use Csj (the component selector to pick the appropriate image components from the scan header. [1] https://www.w3.org/Graphics/JPEG/itu-t81.pdf, A.2.2 [2] https://www.w3.org/Graphics/JPEG/itu-t81.pdf, B.2.3
--- a/sys/src/cmd/jpg/readjpg.c
+++ b/sys/src/cmd/jpg/readjpg.c
@@ -457,7 +457,7 @@
return 0;
}
if(Bread(h->fd, tmp, 2) != 2)
- Readerr:
+Readerr:
jpgerror(h, readerr);
n = int2(tmp, 0);
if(n < 2)
@@ -574,7 +574,7 @@
t->shift[v] = 8-cnt;
t->value[v] = t->val[t->valptr[i]+(code-t->mincode[i])];
- continueBytes:
+continueBytes:
v++;
}
@@ -899,16 +899,15 @@
void
progressivedc(Header *h, int comp, int Ah, int Al)
{- int Ns, z, ri, mcu, nmcu;
+ int Ns, z, ri, mcu, nmcu;
int block, t, diff, qt, *dc, bn;
+ int x, y, H, V, nhor, nver, q;
Huffman *dcht;
uchar *ss;
- int i, Td[3], DC[3], blockno[3];
+ int i, j, Td[4], DC[4], scancomp[4], blockno[4];
ss= h->ss;
Ns = ss[0];
- if(Ns!=1 && Ns!=h->Nf)
- jpgerror(h, "ReadJPG: can't handle progressive with Ns!=1 and Nf!=Ns in DC scan");
/* initialize data structures */
h->cnt = 0;
@@ -916,47 +915,81 @@
h->peek = -1;
for(i=0; i<Ns; i++){- /*
- * JPEG requires scan components to be in same order as in frame,
- * so if both have 3 we know scan is Y Cb Cr and there's no need to
- * reorder
- */
nibbles(ss[2+2*i], &Td[i], &z); /* z is ignored */
DC[i] = 0;
+ for(j=0; j<h->Nf; j++)
+ if(h->comp[j].C == ss[1+2*i]){+ scancomp[i] = j;
+ break;
+ }
+ if(j == h->Nf)
+ jpgerror(h, "ReadJPG: bad component selector in scan");
}
ri = h->ri;
- nmcu = h->nacross*h->ndown;
- memset(blockno, 0, sizeof blockno);
- for(mcu=0; mcu<nmcu; ){- for(i=0; i<Ns; i++){- if(Ns != 1) comp = i;
-
- dcht = &h->dcht[Td[i]];
- qt = h->qt[h->comp[comp].Tq][0];
- dc = h->dccoeff[comp];
- bn = blockno[i];
-
- for(block=0; block<h->nblock[comp]; block++){+ if(Ns == 1){+ /* ITU-T.81 A.2.2: scan in raster order if Ns = 1*/
+ comp = scancomp[0];
+ H = h->comp[comp].H;
+ V = h->comp[comp].V;
+ q = 8*h->Hmax/H;
+ nhor = (h->X+q-1)/q;
+ q = 8*h->Vmax/V;
+ nver = (h->Y+q-1)/q;
+ dcht = &h->dcht[Td[0]];
+ qt = h->qt[h->comp[comp].Tq][0];
+ dc = h->dccoeff[comp];
+ mcu = 0;
+ for(y=0; y<nver; y++){+ for(x=0; x<nhor; x++){+ bn = (x/H + h->nacross*(y/V))*H*V + H*(y%V) + x%H;
if(Ah == 0){t = decode(h, dcht);
diff = receive(h, t);
- DC[i] += diff;
- dc[bn] = qt*DC[i]<<Al;
+ DC[0] += diff;
+ dc[bn] = qt*DC[0]<<Al;
}else
dc[bn] |= qt*receivebit(h)<<Al;
- bn++;
+ /* process restart marker, if present */
+ mcu++;
+ if(ri>0 && mcu%ri==0){+ restart(h, mcu);
+ DC[0] = 0;
+ }
}
- blockno[i] = bn;
}
-
- /* process restart marker, if present */
- mcu++;
- if(ri>0 && mcu<nmcu && mcu%ri==0){- restart(h, mcu);
- for(i=0; i<Ns; i++)
- DC[i] = 0;
+ }else{+ /* ITU-T.81 A.2.3: scan in MCU order otherwise */
+ nmcu = h->nacross*h->ndown;
+ memset(blockno, 0, sizeof blockno);
+ for(mcu=0; mcu<nmcu; ){+ for(i=0; i<Ns; i++){+ comp = scancomp[i];
+ dcht = &h->dcht[Td[i]];
+ qt = h->qt[h->comp[comp].Tq][0];
+ dc = h->dccoeff[comp];
+ bn = blockno[i];
+ for(block=0; block<h->nblock[comp]; block++){+ if(Ah == 0){+ t = decode(h, dcht);
+ diff = receive(h, t);
+ DC[i] += diff;
+ dc[bn] = qt*DC[i]<<Al;
+ }else
+ dc[bn] |= qt*receivebit(h)<<Al;
+ bn++;
+ }
+ blockno[i] = bn;
+ }
+
+ /* process restart marker, if present */
+ mcu++;
+ if(ri>0 && mcu<nmcu && mcu%ri==0){+ restart(h, mcu);
+ for(i=0; i<Ns; i++)
+ DC[i] = 0;
+ }
}
}
}
@@ -1003,7 +1036,7 @@
mcu = 0;
for(y=0; y<nver; y++){ for(x=0; x<nhor; x++){- /* Figure G-3 */
+ /* Figure G-3 */
if(eobrun > 0){--eobrun;
continue;
@@ -1104,7 +1137,7 @@
for(x=0; x<nhor; x++){/* Figure G-7 */
- /* arrange blockno to be in same sequence as original scan calculation. */
+ /* arrange blockno to be in same sequence as original scan calculation. */
tmcu = x/H + (nacross/H)*(y/V);
blockno = tmcu*H*V + H*(y%V) + x%H;
acc = ac[blockno];
@@ -1237,7 +1270,9 @@
static
void
-colormapall1(Header *h, int colorspace, Rawimage *image, int data0[8*8], int data1[8*8], int data2[8*8], int mcu, int nacross)
+colormapall1(Header *h, int colorspace, Rawimage *image,
+ int data0[8*8], int data1[8*8], int data2[8*8],
+ int mcu, int nacross)
{uchar *rpic, *gpic, *bpic, *rp, *gp, *bp;
int *p0, *p1, *p2;
@@ -1290,7 +1325,10 @@
static
void
-colormap(Header *h, int colorspace, Rawimage *image, int *data0[8*8], int *data1[8*8], int *data2[8*8], int mcu, int nacross, int Hmax, int Vmax, int *H, int *V)
+colormap(Header *h, int colorspace, Rawimage *image,
+ int *data0[8*8], int *data1[8*8], int *data2[8*8],
+ int mcu, int nacross, int Hmax, int Vmax,
+ int *H, int *V)
{uchar *rpic, *gpic, *bpic;
int x, y, dx, dy, minx, miny;
--
⑨