Merge pull request #1496 from yamasakitomohiro/master

fixes  CGContextDrawImage: invalid context 0x0
https://github.com/rs/SDWebImage/issues/1401
https://github.com/rs/SDWebImage/issues/1454
https://github.com/rs/SDWebImage/issues/1457

@@ -22,20 +22,17 @@
     @autoreleasepool{
         // do not decode animated images
         if (image.images) { return image; }
-    
+        
         CGImageRef imageRef = image.CGImage;
-    
+        
         CGImageAlphaInfo alpha = CGImageGetAlphaInfo(imageRef);
         BOOL anyAlpha = (alpha == kCGImageAlphaFirst ||
                          alpha == kCGImageAlphaLast ||
                          alpha == kCGImageAlphaPremultipliedFirst ||
                          alpha == kCGImageAlphaPremultipliedLast);
-    
+        
         if (anyAlpha) { return image; }
-    
-        size_t width = CGImageGetWidth(imageRef);
-        size_t height = CGImageGetHeight(imageRef);
-    
+        
         // current
         CGColorSpaceModel imageColorSpaceModel = CGColorSpaceGetModel(CGImageGetColorSpace(imageRef));
         CGColorSpaceRef colorspaceRef = CGImageGetColorSpace(imageRef);
@@ -43,19 +40,26 @@
         bool unsupportedColorSpace = (imageColorSpaceModel == 0 || imageColorSpaceModel == -1 || imageColorSpaceModel == kCGColorSpaceModelCMYK || imageColorSpaceModel == kCGColorSpaceModelIndexed);
         if (unsupportedColorSpace)
             colorspaceRef = CGColorSpaceCreateDeviceRGB();
-    
-        CGContextRef context = CGBitmapContextCreate(NULL, width,
+        
+        size_t width = CGImageGetWidth(imageRef);
+        size_t height = CGImageGetHeight(imageRef);
+        NSUInteger bytesPerPixel = 4;
+        NSUInteger bytesPerRow = bytesPerPixel * width;
+        NSUInteger bitsPerComponent = 8;
+        
+        CGContextRef context = CGBitmapContextCreate(NULL,
+                                                     width,
                                                      height,
-                                                     CGImageGetBitsPerComponent(imageRef),
-                                                     0,
+                                                     bitsPerComponent,
+                                                     bytesPerRow,
                                                      colorspaceRef,
                                                      kCGBitmapByteOrderDefault | kCGImageAlphaPremultipliedFirst);
-    
+        
         // 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 scale:image.scale orientation:image.imageOrientation];
-    
+        
         if (unsupportedColorSpace)
             CGColorSpaceRelease(colorspaceRef);