From 13bffef91d0406dbd394ec375e7f5e4a43411f9e Mon Sep 17 00:00:00 2001
From: Kylian Ronfleux--Corail <35237015+Kyliroco@users.noreply.github.com>
Date: Thu, 10 Apr 2025 10:01:02 +0000
Subject: [PATCH] Fix quantization table scaling when quality is applied to
 custom qtables

When both a custom quantization table and a quality value are provided,
the quantization table should be scaled using the JPEG quality scaling factor.
If quality is not explicitly set, the default base quality of 50 is used to preserve the original table.
This ensures consistent behavior when saving JPEGs with custom qtables.

Fixes part of the issue with applying 'quality' to 'qtables'.
---
 src/libImaging/JpegEncode.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/libImaging/JpegEncode.c b/src/libImaging/JpegEncode.c
index a2e2945bc..24e2c76ba 100644
--- a/src/libImaging/JpegEncode.c
+++ b/src/libImaging/JpegEncode.c
@@ -173,7 +173,7 @@ ImagingJpegEncode(Imaging im, ImagingCodecState state, UINT8 *buf, int bytes) {
             /* Use custom quantization tables */
             if (context->qtables) {
                 int i;
-                int quality = 100;
+                int quality = 50;
                 int last_q = 0;
                 if (context->quality != -1) {
                     quality = context->quality;