fix unsupported parameter combination issues

when CGBitmapContextCreate is called

SDWebImage/SDWebImageDecoder.m

@@ -13,60 +13,38 @@
 @implementation UIImage (ForceDecode)
 
 + (UIImage *)decodedImageWithImage:(UIImage *)image {
-    if (image.images) {
-        // Do not decode animated images
-        return image;
-    }
+    // do not decode animated images
+    if (image.images) { return image; }
 
     CGImageRef imageRef = image.CGImage;
-    CGSize imageSize = CGSizeMake(CGImageGetWidth(imageRef), CGImageGetHeight(imageRef));
-    CGRect imageRect = (CGRect){.origin = CGPointZero, .size = imageSize};
 
-    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
-    CGBitmapInfo bitmapInfo = CGImageGetBitmapInfo(imageRef);
+    CGImageAlphaInfo alpha = CGImageGetAlphaInfo(imageRef);
+    BOOL anyAlpha = (alpha == kCGImageAlphaFirst ||
+                     alpha == kCGImageAlphaLast ||
+                     alpha == kCGImageAlphaPremultipliedFirst ||
+                     alpha == kCGImageAlphaPremultipliedLast);
 
-    int infoMask = (bitmapInfo & kCGBitmapAlphaInfoMask);
-    BOOL anyNonAlpha = (infoMask == kCGImageAlphaNone ||
-            infoMask == kCGImageAlphaNoneSkipFirst ||
-            infoMask == kCGImageAlphaNoneSkipLast);
+    if (anyAlpha) { return image; }
 
-    // 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;
+    size_t width = CGImageGetWidth(imageRef);
+    size_t height = CGImageGetHeight(imageRef);
 
-        // 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;
-    }
+    CGContextRef context = CGBitmapContextCreate(NULL, width,
+                                                 height,
+                                                 CGImageGetBitsPerComponent(imageRef),
+                                                 0,
+                                                 CGImageGetColorSpace(imageRef),
+                                                 kCGBitmapByteOrderDefault | 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;
-
-    CGContextDrawImage(context, imageRect, imageRef);
-    CGImageRef decompressedImageRef = CGBitmapContextCreateImage(context);
+    // Draw the image into the context and retrieve the new image, which will now have an alpha layer
+    CGContextDrawImage(context, CGRectMake(0, 0, width, height), imageRef);
+    CGImageRef imageRefWithAlpha = CGBitmapContextCreateImage(context);
+    UIImage *imageWithAlpha = [UIImage imageWithCGImage:imageRefWithAlpha];
 
     CGContextRelease(context);
+    CGImageRelease(imageRefWithAlpha);
 
-    UIImage *decompressedImage = [UIImage imageWithCGImage:decompressedImageRef scale:image.scale orientation:image.imageOrientation];
-    CGImageRelease(decompressedImageRef);
-    return decompressedImage;
+    return imageWithAlpha;
 }
 
 @end