Remove alpha channel from UIImage

Question

I use the following method to get a decompressed uiimage from file system. However the UIImageView is colored as red when I turn on the color blended layer, even though the UIImageView is set to Opaque.

The images on file system don't have alpha channel. I tried set CGContextSetAlpha(bitmapContext, 1), but still has blended layer.

Anyone know how to remove alpha channel when using CGContextDrawImage?

- (UIImage *)decompressedImage
{
    CGImageRef imageRef = self.CGImage;
    CGRect rect = CGRectMake(0.f, 0.f, CGImageGetWidth(imageRef), CGImageGetHeight(imageRef));
    CGContextRef bitmapContext = CGBitmapContextCreate(NULL,
                                                       rect.size.width,
                                                       rect.size.height,
                                                       CGImageGetBitsPerComponent(imageRef),
                                                       CGImageGetBytesPerRow(imageRef),
                                                       CGImageGetColorSpace(imageRef),
                                                       kCGImageAlphaPremultipliedFirst | kCGBitmapByteOrder32Little
                                                       );
    // kCGImageAlphaPremultipliedFirst | kCGBitmapByteOrder32Little are the bit flags required
    //  so that the main thread doesn't have any conversions to do.

    CGContextDrawImage(bitmapContext, rect, imageRef);

    CGImageRef decompressedImageRef = CGBitmapContextCreateImage(bitmapContext);
    UIImage* decompressedImage = [UIImage imageWithCGImage:decompressedImageRef
                                                     scale:[[UIScreen mainScreen] scale]
                                               orientation:UIImageOrientationUp];
    CGImageRelease(decompressedImageRef);
    CGContextRelease(bitmapContext);

    return decompressedImage;
}

Answer 1

In the options for the context, try the option

kCGImageAlphaNoneSkipLast

or

kCGImageAlphaNoneSkipFirst

Depending on if you are using RGBA or ARGB

ie,

CGContextRef bitmapContext = CGBitmapContextCreate(NULL,
                                                       rect.size.width,
                                                       rect.size.height,
                                                       CGImageGetBitsPerComponent(imageRef),
                                                       CGImageGetBytesPerRow(imageRef),
                                                       CGImageGetColorSpace(imageRef),
                                                       kCGImageAlphaNoneSkipLast | kCGBitmapByteOrder32Little
                                                       );