diff --git a/apps/plugins/jpeg/jpeg.c b/apps/plugins/jpeg/jpeg.c
index 5f9999a..945e2d2 100644
--- a/apps/plugins/jpeg/jpeg.c
+++ b/apps/plugins/jpeg/jpeg.c
@@ -935,6 +935,7 @@ int load_and_show(char* filename)
     struct t_disp* p_disp; /* currenly displayed image */
     int cx, cy; /* view center */
 
+DEBUGF("read jpeg file %s\n",filename);
     fd = rb->open(filename, O_RDONLY);
     if (fd < 0)
     {
diff --git a/apps/plugins/jpeg/jpeg_decoder.c b/apps/plugins/jpeg/jpeg_decoder.c
index 71d5088..bc27227 100644
--- a/apps/plugins/jpeg/jpeg_decoder.c
+++ b/apps/plugins/jpeg/jpeg_decoder.c
@@ -560,7 +560,17 @@ int process_markers(unsigned char* p_src, long size, struct jpeg* p_jpeg)
                     if (p_jpeg->frameheader[i].horizontal_sampling > 2
                      || p_jpeg->frameheader[i].vertical_sampling > 2)
                     return -3; /* Unsupported SOF0 subsampling */
+                    DEBUGF("channel %d hsub %d vsub %d\n",i,p_jpeg->frameheader[i].horizontal_sampling,p_jpeg->frameheader[i].vertical_sampling);
                 }
+                /* Check for subsampled luma, or different per-chroma-channel
+                   subsampling */
+                if (n == 3 && (p_jpeg->frameheader[0].vertical_sampling > 1 ||
+                    p_jpeg->frameheader[0].horizontal_sampling > 1 ||
+                    p_jpeg->frameheader[1].vertical_sampling !=
+                    p_jpeg->frameheader[2].vertical_sampling ||
+                    p_jpeg->frameheader[1].horizontal_sampling !=
+                    p_jpeg->frameheader[2].horizontal_sampling))
+                    return -3;
                 p_jpeg->blocks = n;
             }
             break;
@@ -921,9 +931,10 @@ void build_lut(struct jpeg* p_jpeg)
         p_jpeg->store_pos[i] = i; /* default ordering */
 
     /* assignments for the decoding of blocks */
-    if (p_jpeg->frameheader[0].horizontal_sampling == 2
-        && p_jpeg->frameheader[0].vertical_sampling == 1)
+    if (p_jpeg->frameheader[1].horizontal_sampling == 2
+        && p_jpeg->frameheader[1].vertical_sampling == 1)
     {   /* 4:2:2 */
+DEBUGF("chroma 2x1 subsampled\n");
         p_jpeg->blocks = 4;
         p_jpeg->x_mbl = (p_jpeg->x_size+15) / 16;
         p_jpeg->x_phys = p_jpeg->x_mbl * 16;
@@ -944,9 +955,10 @@ void build_lut(struct jpeg* p_jpeg)
         p_jpeg->subsample_y[1] = 1;
         p_jpeg->subsample_y[2] = 1;
     }
-    if (p_jpeg->frameheader[0].horizontal_sampling == 1
-        && p_jpeg->frameheader[0].vertical_sampling == 2)
+    if (p_jpeg->frameheader[1].horizontal_sampling == 1
+        && p_jpeg->frameheader[1].vertical_sampling == 2)
     {   /* 4:2:2 vertically subsampled */
+DEBUGF("chroma 1x2 subsampled\n");
         p_jpeg->store_pos[1] = 2; /* block positions are mirrored */
         p_jpeg->store_pos[2] = 1;
         p_jpeg->blocks = 4;
@@ -969,9 +981,10 @@ void build_lut(struct jpeg* p_jpeg)
         p_jpeg->subsample_y[1] = 2;
         p_jpeg->subsample_y[2] = 2;
     }
-    else if (p_jpeg->frameheader[0].horizontal_sampling == 2
-        && p_jpeg->frameheader[0].vertical_sampling == 2)
+    else if (p_jpeg->frameheader[1].horizontal_sampling == 2
+        && p_jpeg->frameheader[1].vertical_sampling == 2)
     {   /* 4:2:0 */
+DEBUGF("chroma 2x2 subsampled\n");
         p_jpeg->blocks = 6;
         p_jpeg->x_mbl = (p_jpeg->x_size+15) / 16;
         p_jpeg->x_phys = p_jpeg->x_mbl * 16;
@@ -996,10 +1009,11 @@ void build_lut(struct jpeg* p_jpeg)
         p_jpeg->subsample_y[1] = 2;
         p_jpeg->subsample_y[2] = 2;
     }
-    else if (p_jpeg->frameheader[0].horizontal_sampling == 1
-        && p_jpeg->frameheader[0].vertical_sampling == 1)
+    else if (p_jpeg->frameheader[1].horizontal_sampling == 1
+        && p_jpeg->frameheader[1].vertical_sampling == 1)
     {   /* 4:4:4 */
         /* don't overwrite p_jpeg->blocks */
+DEBUGF("chroma not subsampled\n");
         p_jpeg->x_mbl = (p_jpeg->x_size+7) / 8;
         p_jpeg->x_phys = p_jpeg->x_mbl * 8;
         p_jpeg->y_mbl = (p_jpeg->y_size+7) / 8;