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heifsave: clip out of range values when packing 16-bit to 8-bit #4524

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heifsave: clip out of range values when packing 16-bit to 8-bit #4524

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@kleisauke kleisauke commented May 19, 2025 •
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Test case:

$ cat <<EOT > sharpen-mild.mat
3 3 24
-1 -1 -1
-1 32 -1
-1 -1 -1
EOT
$ vips convf x.jpg x.avif sharpen-mild.mat

Where x.jpg is the image mentioned at lovell/sharp#4344 (comment).

Note that this only reproduces on the master branch when applying the following patch:

--- a/libvips/foreign/foreign.c
+++ b/libvips/foreign/foreign.c
@@ -1529,6 +1529,8 @@ vips__foreign_convert_saveable(VipsImage *in, VipsImage **ready,
 	VipsForeignSaveable saveable, VipsBandFormat *format, VipsCoding *coding,
 	VipsArrayDouble *background)
 {
+	VipsBandFormat original_format = in->BandFmt;
+
 	VipsImage *out;
 
 	/* in holds a reference to the output of our chain as we build it.
@@ -1642,7 +1644,7 @@ vips__foreign_convert_saveable(VipsImage *in, VipsImage **ready,
 	/* Convert to the format the saver likes.
 	 */
 	if (in->Coding == VIPS_CODING_NONE) {
-		if (vips_cast(in, &out, format[in->BandFmt], NULL)) {
+		if (vips_cast(in, &out, format[original_format], NULL)) {
 			g_object_unref(in);
 			return -1;
 		}

or when checking out a commit prior to 9f590ce. Otherwise, the image is cast to uchar just before writing.

(To simplify testing, this PR is rebased upon d87f9ed)

@kleisauke kleisauke mentioned this pull request May 19, 2025
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@kleisauke kleisauke force-pushed the heifsave-clip-ushort branch from 6a800cc to de23de1 Compare May 20, 2025 07:53
@kleisauke kleisauke changed the title heifsave: clip out of range values for 16-bit input to 8-bit output heifsave: clip out of range values when packing 16-bit to 8-bit May 20, 2025
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