From 97746fb574e79060e7a672102c30604eb34d20f8 Mon Sep 17 00:00:00 2001
From: Jamie Mansfield <jmansfield@cadixdev.org>
Date: Thu, 14 Aug 2025 00:48:33 +0100
Subject: [PATCH] LibGfx: Fix colour with Photoshop JPEG files using CMYK

This is based on the original functionality Lucus wrote prior to using
libjpeg.

Co-authored-by: Lucas CHOLLET <lucas.chollet@free.fr>
---
 Libraries/LibGfx/ImageFormats/JPEGLoader.cpp | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/Libraries/LibGfx/ImageFormats/JPEGLoader.cpp b/Libraries/LibGfx/ImageFormats/JPEGLoader.cpp
index 886ec6d259c..143e9ba8444 100644
--- a/Libraries/LibGfx/ImageFormats/JPEGLoader.cpp
+++ b/Libraries/LibGfx/ImageFormats/JPEGLoader.cpp
@@ -145,6 +145,24 @@ ErrorOr<void> JPEGLoadingContext::decode()
                 }
             }
         }
+
+        // Photoshop writes inverted CMYK data (i.e. Photoshop's 0 should be 255). We convert this
+        // to expected values.
+        if (cinfo.saw_Adobe_marker) {
+            for (int i = 0; i < cmyk_bitmap->size().height(); ++i) {
+                auto* line = cmyk_bitmap->scanline(i);
+
+                for (int j = 0; j < cmyk_bitmap->size().width(); ++j) {
+                    auto const& cmyk = line[j];
+                    line[j] = {
+                        static_cast<u8>(255 - cmyk.c),
+                        static_cast<u8>(255 - cmyk.m),
+                        static_cast<u8>(255 - cmyk.y),
+                        static_cast<u8>(255 - cmyk.k),
+                    };
+                }
+            }
+        }
     }
 
     JOCTET* icc_data_ptr = nullptr;