From de19c24241628c79235e6938e485b1f4c70673d9 Mon Sep 17 00:00:00 2001
From: Martin Conte Mac Donell <Reflejo@gmail.com>
Date: Wed, 13 Feb 2013 21:55:26 -0300
Subject: [PATCH] [BUG] Fix invalid alpha on JPEG files

---
 SDWebImage/SDWebImageDecoder.m | 37 ++++++++++++++++++++++++++++++++--
 1 file changed, 35 insertions(+), 2 deletions(-)

diff --git a/SDWebImage/SDWebImageDecoder.m b/SDWebImage/SDWebImageDecoder.m
index 1b219c9..fe70fd9 100644
--- a/SDWebImage/SDWebImageDecoder.m
+++ b/SDWebImage/SDWebImageDecoder.m
@@ -18,8 +18,41 @@
     CGSize imageSize = CGSizeMake(CGImageGetWidth(imageRef), CGImageGetHeight(imageRef));
     CGRect imageRect = (CGRect){.origin = CGPointZero, .size = imageSize};
 
-    CGColorSpaceRef colorSpace = CGImageGetColorSpace(imageRef);
-    CGContextRef context = CGBitmapContextCreate(NULL, imageSize.width, imageSize.height, CGImageGetBitsPerComponent(imageRef), CGImageGetBytesPerRow(imageRef), colorSpace, CGImageGetBitmapInfo(imageRef));
+    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
+    CGBitmapInfo bitmapInfo = CGImageGetBitmapInfo(imageRef);
+
+    int infoMask = (bitmapInfo & kCGBitmapAlphaInfoMask);
+    BOOL anyNonAlpha = (infoMask == kCGImageAlphaNone ||
+                        infoMask == kCGImageAlphaNoneSkipFirst ||
+                        infoMask == kCGImageAlphaNoneSkipLast);
+
+    // CGBitmapContextCreate doesn't support kCGImageAlphaNone with RGB.
+    // https://developer.apple.com/library/mac/#qa/qa1037/_index.html
+    if (infoMask == kCGImageAlphaNone && CGColorSpaceGetNumberOfComponents(colorSpace) > 1)
+    {
+        // Unset the old alpha info.
+        bitmapInfo &= ~kCGBitmapAlphaInfoMask;
+       
+        // Set noneSkipFirst.
+        bitmapInfo |= kCGImageAlphaNoneSkipFirst;
+    }
+    // Some PNGs tell us they have alpha but only 3 components. Odd.
+    else if (!anyNonAlpha && CGColorSpaceGetNumberOfComponents(colorSpace) == 3)
+    {
+        // Unset the old alpha info.
+        bitmapInfo &= ~kCGBitmapAlphaInfoMask;
+        bitmapInfo |= kCGImageAlphaPremultipliedFirst;
+    }
+
+    // It calculates the bytes-per-row based on the bitsPerComponent and width arguments.
+    CGContextRef context = CGBitmapContextCreate(NULL,
+                                                 imageSize.width,
+                                                 imageSize.height,
+                                                 CGImageGetBitsPerComponent(imageRef),
+                                                 0,
+                                                 colorSpace,
+                                                 bitmapInfo);
+    CGColorSpaceRelease(colorSpace);
 
     // If failed, return undecompressed image
     if (!context) return image;