Polish JPEG chroma subsampling handling (#4167)

kleisauke · web-flow · commit f5025a4b50c6 · 2024-09-21T17:47:54.000+01:00
Non-functional change.
diff --git a/libvips/foreign/vips2jpeg.c b/libvips/foreign/vips2jpeg.c
@@ -667,30 +667,21 @@ set_cinfo(struct jpeg_compress_struct *cinfo,
 	if (progressive)
 		jpeg_simple_progression(cinfo);
 
-	if (in->Bands != 3 ||
-		subsample_mode == VIPS_FOREIGN_SUBSAMPLE_OFF ||
-		(subsample_mode == VIPS_FOREIGN_SUBSAMPLE_AUTO &&
-			qfac >= 90))
-		/* No chroma subsample.
-		 */
-		for (int i = 0; i < in->Bands; i++) {
-			cinfo->comp_info[i].h_samp_factor = 1;
-			cinfo->comp_info[i].v_samp_factor = 1;
-		}
-	else {
-		/* Use 4:2:0 subsampling, we must set this explicitly, since some
-		 * jpeg libraries do not enable chroma subsample by default.
-		 */
-		cinfo->comp_info[0].h_samp_factor = 2;
-		cinfo->comp_info[0].v_samp_factor = 2;
+	/* We must set chroma subsampling explicitly since some libjpegs do not
+	 * enable this by default.
+	 */
+	if (in->Bands == 3 &&
+		(subsample_mode == VIPS_FOREIGN_SUBSAMPLE_ON ||
+			(subsample_mode == VIPS_FOREIGN_SUBSAMPLE_AUTO &&
+				qfac < 90)))
+		cinfo->comp_info[0].h_samp_factor = cinfo->comp_info[0].v_samp_factor = 2;
+	else
+		cinfo->comp_info[0].h_samp_factor = cinfo->comp_info[0].v_samp_factor = 1;
 
-		/* Rest should have sampling factors 1,1.
-		 */
-		for (int i = 1; i < in->Bands; i++) {
-			cinfo->comp_info[i].h_samp_factor = 1;
-			cinfo->comp_info[i].v_samp_factor = 1;
-		}
-	}
+	/* Rest should have sampling factors 1,1.
+	 */
+	for (int i = 1; i < in->Bands; i++)
+		cinfo->comp_info[i].h_samp_factor = cinfo->comp_info[i].v_samp_factor = 1;
 
 	/* Only write the JFIF headers if we have no EXIF.
 	 * Some readers get confused if you set both.
diff --git a/libvips/foreign/vips2tiff.c b/libvips/foreign/vips2tiff.c
@@ -691,15 +691,16 @@ wtiff_compress_jpeg_header(Wtiff *wtiff,
 	/* We must set chroma subsampling explicitly since some libjpegs do not
 	 * enable this by default.
 	 */
-	for (int i = 0; i < image->Bands; i++) {
-		cinfo->comp_info[i].h_samp_factor = 1;
-		cinfo->comp_info[i].v_samp_factor = 1;
-	}
 	if (image->Bands == 3 &&
-		wtiff->Q < 90) {
-		cinfo->comp_info[0].h_samp_factor = 2;
-		cinfo->comp_info[0].v_samp_factor = 2;
-	}
+		wtiff->Q < 90)
+		cinfo->comp_info[0].h_samp_factor = cinfo->comp_info[0].v_samp_factor = 2;
+	else
+		cinfo->comp_info[0].h_samp_factor = cinfo->comp_info[0].v_samp_factor = 1;
+
+	/* Rest should have sampling factors 1,1.
+	 */
+	for (int i = 1; i < image->Bands; i++)
+		cinfo->comp_info[i].h_samp_factor = cinfo->comp_info[i].v_samp_factor = 1;
 
 	/* For low Q, we write YCbCr, for high Q, RGB. The jpeg coeffs don't
 	 * encode the photometric interpretation, the tiff header does that,
