CGImageCreateWithMask图像编码与alpha通道反转

Question

/ 注意，我已修复代码..查找编辑备注 /

对于iOS 5.0+，为了在iPad上运行，我创建了一个功能，允许用户屏蔽输入图像，生成两个新图像，一个前景图像和一个背景图像。当我将这些添加到UIImageView，并在设备或模拟器上显示时，我得到了我期望的结果。

但是，当我通过将数据编码为会话数据来保存这些数据时，生成的图像是向后的（即图像遮罩已被反转）。我们两个人已经运行了代码，没有任何地方被反转，没有复制/粘贴错误。我以为kCGImageAlphaPremultipliedFirst和kCGImageAlphaPremultipliedLast可能有什么关系。当我对乱码图像进行编码时，它们从kCGImageAlphaPremultipliedFirst开始，当它们被加载时，它们是kCGImageAlphaPremultipliedLast。

任何帮助或想法都会非常感激。

艾米@ InsatiableGenius

以下功能通过以下方式调用：

[self createMask]; 
[self addImageAndBackground:foregroundImg backgroundImg:backgroundImg];


- (UIImage*)maskImage:(UIImage *)image withMask:(UIImage *)maskImage {
    CGImageRef maskRef = maskImage.CGImage;
    CGImageRef mask = CGImageMaskCreate(CGImageGetWidth(maskRef),
                                        CGImageGetHeight(maskRef),
                                        CGImageGetBitsPerComponent(maskRef),
                                        CGImageGetBitsPerPixel(maskRef),
                                        CGImageGetBytesPerRow(maskRef),
                                        CGImageGetDataProvider(maskRef), NULL, false);

    CGImageRef sourceImage = [image CGImage];
    CGImageRef imageWithAlpha = sourceImage;
      if ((CGImageGetAlphaInfo(sourceImage) == kCGImageAlphaNone)
         || (CGImageGetAlphaInfo(sourceImage) == kCGImageAlphaNoneSkipFirst)
        || (CGImageGetAlphaInfo(sourceImage) == kCGImageAlphaNoneSkipLast)) {
         imageWithAlpha = CopyImageAndAddAlphaChannel(sourceImage);
     }

    CGImageRef masked = CGImageCreateWithMask(imageWithAlpha, mask);
    CGImageRelease(mask);

    if (sourceImage != imageWithAlpha) {
        CGImageRelease(imageWithAlpha);
    }

    UIImage* retImage = [UIImage imageWithCGImage:masked];
    CGImageRelease(masked);


    /* EDIT STARTS HERE return retImage; */

//Added extra render step to force it to save correct alpha values (not the mask)
UIImage* retImage = [UIImage imageWithCGImage:masked];
CGImageRelease(masked);

UIGraphicsBeginImageContext(retImage.size);
[retImage drawAtPoint:CGPointZero];
UIImage *newImg = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
retImage = nil;

return newImg;

}


-(void)createMask{

    //take whole screen uiimage from paintview
    //user painted black for mask, set rest of window to white
    [paintView setWhiteBackground:YES];
    //get user painted mask
    UIImage *maskFromPaint  = [paintView allocNormalResImageWithBlur:NO/*blur?*/];
     [self dumpTestImg:maskFromPaint name:@"maskFromPaint"];
    UIImage *maskNoAlpha = [maskFromPaint resetImageAlpha:1.0];
    [self dumpTestImg:maskNoAlpha name:@"maskFromPaintNoAlpha"];

    //mask has to be gray
    UIImage *maskFromPaintGray = [self convertImageToGrayScale:maskNoAlpha];
     [self dumpTestImg:maskFromPaintGray name:@"maskFromPaintGray"];

    //Had to call this normalize function because some pngs are not compatiable (8 bit)
    UIImage *disp_original = [[UIImage alloc] initWithCGImage:[[original normalize] CGImage] ];
    //Resize original to screen size (alternatively we could upscale the paint... not sure which for now)
    disp_original = [disp_original resizedImageWithContentMode:UIViewContentModeScaleAspectFit bounds:inputImageView.frame.size interpolationQuality:kCGInterpolationHigh] ;

   CGSize imageInViewSize = disp_original.size;

    //use size of displayed original to crop the paintview
    CGRect overlayRect = CGRectMake((int)(inputImageView.frame.size.width - imageInViewSize.width) / 2,
                                    (int)(inputImageView.frame.size.height - imageInViewSize.height) / 2, 
                                    (int)imageInViewSize.width, 
                                    (int)imageInViewSize.height);

    //here is the actual crop
    //get rectangle from paint that is the same size as the displayed original
    CGImageRef maskFromPaintimageRef = CGImageCreateWithImageInRect([maskFromPaintGray CGImage], overlayRect);

    UIImage *invertedMaskFromPaint = [UIImage imageWithCGImage:maskFromPaintimageRef];

     self.maskImg  = [self invertImage:invertedMaskFromPaint];

     [self dumpTestImg:self.maskImg name:@"maskFromPaintCropped"];


    self.backgroundImg = [self    maskImage:disp_original withMask:self.maskImg];
    self.foregroundImg = [self    maskImage:disp_original withMask:invertedMaskFromPaint];

    foregroundImgView.image = foregroundImg;
    backgroundImgView.image = backgroundImg;

    foregroundImgView.hidden =NO;
    backgroundImgView.hidden =NO;
    [container bringSubviewToFront:foregroundImgView];
    [container bringSubviewToFront:backgroundImgView];

    [self dumpTestImg:foregroundImg name:@"foregroundImg"];
    [self dumpTestImg:backgroundImg name:@"backgroundImg"];
    //cleanup
    CGImageRelease(maskFromPaintimageRef);
    maskFromPaint = nil;
    maskFromPaintGray = nil;
    maskNoAlpha = nil;
    disp_original = nil;

    //put things back
    [paintView setWhiteBackground:NO];

}


CGImageRef CopyImageAndAddAlphaChannel(CGImageRef sourceImage) {

    CGImageRef retVal = NULL;

    size_t width = CGImageGetWidth(sourceImage);

    size_t height = CGImageGetHeight(sourceImage);

    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

    CGContextRef offscreenContext = CGBitmapContextCreate(NULL, width, height,

                                                          8, 0, colorSpace,   kCGImageAlphaPremultipliedLast );  


    if (offscreenContext != NULL) {

        CGContextDrawImage(offscreenContext, CGRectMake(0, 0, width, height), sourceImage);

        retVal = CGBitmapContextCreateImage(offscreenContext);

        CGContextRelease(offscreenContext);

    }

    CGColorSpaceRelease(colorSpace);

    return retVal;

}


- (UIImage*)invertImage:(UIImage *)sourceImage {
    CIContext *context = [CIContext contextWithOptions:nil];
    CIFilter *filter= [CIFilter filterWithName:@"CIColorInvert"];
    CIImage *inputImage = [[CIImage alloc] initWithImage:sourceImage];
    [filter setValue:inputImage forKey:@"inputImage"];
    return [UIImage imageWithCGImage:[context createCGImage:filter.outputImage fromRect:filter.outputImage.extent]];

}


-(void)addImageAndBackground:(UIImage *)foregroundImgIn backgroundImg:(UIImage *)backgroundImgIn{
    UIImageView *tmpIV;

    UIImageView *imgVF = [[UIImageView alloc] initWithImage:  foregroundImgIn];
    imgVF.userInteractionEnabled = YES;
    [self dumpTestImg:foregroundImgIn name:@"foregroundIn"];

    UIImageView *imgVB = [[UIImageView alloc] initWithImage:  backgroundImgIn];
    imgVB.userInteractionEnabled = YES;
    [self dumpTestImg:backgroundImgIn name:@"backgroundIn"];

}