iPhone CGContextRef CGBitmapContextCreate 不支持的参数组合

Question

在我的应用程序中，我需要调整和裁剪一些本地和在线存储的图像。我正在使用Trevor Harmon's tutorial它实现了UIImage+Resize。

在我的 iPhone 4(iOS 4.3.1) 上一切正常，没有任何问题。但在我的 iPhone 3G (iOS 3.2) 上，调整大小和裁剪方法不适用于任何图片(本地存储的图片是 PNG)。这是控制台输出:

Tue Apr  5 02:34:44 Andreis-MacBook-Pro.local Puzzle[12453] <Error>: CGBitmapContextCreate:     unsupported parameter combination: 8 integer bits/component; 32 bits/pixel; 3-component color space; kCGImageAlphaLast; 288 bytes/row.
Tue Apr  5 02:34:44 Andreis-MacBook-Pro.local Puzzle[12453] <Error>: CGBitmapContextCreate: unsupported parameter combination: 8 integer bits/component; 32 bits/pixel; 3-component color space; kCGImageAlphaLast; 288 bytes/row.
Tue Apr  5 02:34:44 Andreis-MacBook-Pro.local Puzzle[12453] <Error>: CGBitmapContextCreate: unsupported parameter combination: 8 integer bits/component; 32 bits/pixel; 3-component color space; kCGImageAlphaLast; 288 bytes/row.
Tue Apr  5 02:34:44 Andreis-MacBook-Pro.local Puzzle[12453] <Error>: CGBitmapContextCreate: unsupported parameter combination: 8 integer bits/component; 32 bits/pixel; 3-component color space; kCGImageAlphaLast; 288 bytes/row.

这是裁剪方法

- (UIImage *)croppedImage:(CGRect)bounds 
{
    CGImageRef imageRef = CGImageCreateWithImageInRect([self CGImage], bounds);
    UIImage *croppedImage = [UIImage imageWithCGImage:imageRef];
    CGImageRelease(imageRef);
    return croppedImage;
}

调整大小的方法是这样的:

- (UIImage *)resizedImage:(CGSize)newSize
            transform:(CGAffineTransform)transform
       drawTransposed:(BOOL)transpose
 interpolationQuality:(CGInterpolationQuality)quality 
{
    CGRect newRect = CGRectIntegral(CGRectMake(0, 0, newSize.width, newSize.height));
    CGRect transposedRect = CGRectMake(0, 0, newRect.size.height, newRect.size.width);
    CGImageRef imageRef = self.CGImage;

    CGContextRef bitmap = CGBitmapContextCreate(NULL,
                                            newRect.size.width,
                                            newRect.size.height,
                                            CGImageGetBitsPerComponent(imageRef),
                                            0,
                                            CGImageGetColorSpace(imageRef),
                                            CGImageGetBitmapInfo(imageRef));
    if(bitmap == nil)
        return nil;

    CGContextConcatCTM(bitmap, transform);

    CGContextSetInterpolationQuality(bitmap, quality);

    CGContextDrawImage(bitmap, transpose ? transposedRect : newRect, imageRef);

    CGImageRef newImageRef = CGBitmapContextCreateImage(bitmap);
    UIImage *newImage = [UIImage imageWithCGImage:newImageRef];

    CGContextRelease(bitmap);
    CGImageRelease(newImageRef);

    return newImage;
}

有人可以向我解释一下我遇到这个问题的方式吗？

谢谢你，安德烈

Answer 1

之所以在这里回复，是因为当我收到此错误时，我的像素格式完全相同。我希望这个答案对某人有所帮助。

就我而言，失败的原因是 kCGImageAlphaLast 在 iOS 8 上不再是允许的值，尽管它在 iOS 7 上运行良好。仅 32 pbb、8 bpc 组合允许使用 kCGImageAlphaNoneSkip* 和 kCGImageAlphaPremultiplied* 作为 Alpha 信息。显然这一直是一个问题，但在 iOS 8 之前并没有强制执行。这是我的解决方案:

- (CGBitmapInfo)normalizeBitmapInfo:(CGBitmapInfo)oldBitmapInfo {
    //extract the alpha info by resetting everything else
    CGImageAlphaInfo alphaInfo = oldBitmapInfo & kCGBitmapAlphaInfoMask;

    //Since iOS8 it's not allowed anymore to create contexts with unmultiplied Alpha info
    if (alphaInfo == kCGImageAlphaLast) {
        alphaInfo = kCGImageAlphaPremultipliedLast;
    }
    if (alphaInfo == kCGImageAlphaFirst) {
        alphaInfo = kCGImageAlphaPremultipliedFirst;
    }

    //reset the bits
    CGBitmapInfo newBitmapInfo = oldBitmapInfo & ~kCGBitmapAlphaInfoMask;

    //set the bits to the new alphaInfo
    newBitmapInfo |= alphaInfo;

    return newBitmapInfo;
}

在我的例子中，失败的代码如下所示，其中 imageRef 是从应用程序包加载的 PNG 的 CGImageRef:

CGContextRef bitmap = CGBitmapContextCreate(NULL,
                                                newRect.size.width,
                                                newRect.size.height,
                                                CGImageGetBitsPerComponent(imageRef),
                                                0,
                                                CGImageGetColorSpace(imageRef),
                                                CGImageGetBitmapInfo(imageRef));

来源: https://stackoverflow.com/a/19345325/3099609

https://developer.apple.com/library/mac/DOCUMENTATION/GraphicsImaging/Conceptual/drawingwithquartz2d/dq_context/dq_context.html#//apple_ref/doc/uid/TP30001066-CH203-BCIBHHBB