CGImageCreateWithMaskingColors不适用于iOS7 [英] CGImageCreateWithMaskingColors Doesn't Work with iOS7

问题描述

我在iOS5和iOS6上开发了一款应用。在我升级到XCode 5和iOS7之后，我有一些新的bug。

I've developed an app on iOS5 and iOS6. After I upgraded to XCode 5 and iOS7, I have some new bugs to play with.

主要的是colorMasking不再有效。完全相同的代码仍可编译并适用于iOS6手机。在iOS7上，蒙面颜色仍然存在。我试图在谷歌找到答案，但还没有找到答案。这是iOS7的错误，还是有人知道更好的做彩色掩码的方法？

The main one is the colorMasking no longer works. The exact same code still compiles and works on a phone with iOS6. On iOS7, the masked color is still there. I tried to find the answer on Google, but haven't found an answer. Is it a bug of iOS7, or does anybody know of a better way of doing colormasking?

以下是代码：

- (UIImage*) processImage :(UIImage*) image
{
    UIImage *inputImage = [UIImage imageWithData:UIImageJPEGRepresentation(image, 1.0)];
    const float colorMasking[6]={100.0, 255.0, 0.0, 100.0, 100.0, 255.0};
    CGImageRef imageRef = CGImageCreateWithMaskingColors(inputImage.CGImage, colorMasking);
    UIImage* finalImage = [UIImage imageWithCGImage:imageRef];
    CGImageRelease(imageRef);
    return finalImage;
}

以下是我发现的一些StackOverflow帖子，帮助我在iOS6中运行它第一名：
透明度iOS
iOS颜色在UIImage中透明

Here are a couple StackOverflow posts I found that helped me get it working in iOS6 the first place: Transparency iOS iOS color to transparent in UIImage

推荐答案

我偶然发现 CGImageCreateWithMaskingColors 与 UIImagePNGRepresentation 一起的奇怪行为。这可能与您的问题有关，也可能与您无关。我发现如果：

I have stumbled across some strange behavior of CGImageCreateWithMaskingColors in conjunction with UIImagePNGRepresentation. This may or may not be related to your problem. I have found that if:

1. 如果使用 CGImageCreateWithMaskingColors 并立即添加该图像到图像视图，我可以看到透明度似乎已正确应用;

1. If use CGImageCreateWithMaskingColors and immediately add that image to an image view, I can see that the transparency appears to have been applied correctly;

但在iOS 7中，如果我那么：

But in iOS 7, if I then:

• 从 CGImageCreateWithMaskingColors 中获取此图像并创建 NSData 使用 UIImagePNGRepresentation ;和

• take this image from CGImageCreateWithMaskingColors and create a NSData using UIImagePNGRepresentation; and

如果使用 imageWithData NSData 重新加载图像c $ c>，然后生成的图像将不再具有透明度。

if reload the image from that NSData using imageWithData, then the resulting image will no longer have its transparency.

要确认这一点，如果我<这个 NSData 的code> writeToFile 并在像Photoshop这样的工具中检查保存的图像，我可以确认该文件没有任何应用透明度。

To confirm this, if I writeToFile for this NSData and examine the saved image in a tool like Photoshop, I can confirm that the file does not have any transparency applied.

这仅在iOS 7中显现。在iOS 6中没关系。

This only manifests itself in iOS 7. In iOS 6 it's fine.

但是，如果我在步骤1中拍摄图像并通过 drawInRect 进行往返，则保存图像并随后加载图像的过程相同。

But if I take the image in step 1 and roundtrip it through drawInRect, the same process of saving the image and subsequently loading it works fine.

以下代码说明了问题：

- (UIImage*) processImage :(UIImage*) inputImage
{
    const float colorMasking[6] = {255.0, 255.0, 255.0, 255.0, 255.0, 255.0};
    CGImageRef imageRef = CGImageCreateWithMaskingColors(inputImage.CGImage, colorMasking);
    UIImage* finalImage = [UIImage imageWithCGImage:imageRef];
    CGImageRelease(imageRef);

    // If I put this image in an image view, I see the transparency fine.

    self.imageView.image = finalImage;                           // this works

    // But if I save it to disk and the file does _not_ have any transparency

    NSString *documentsPath           = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES)[0];
    NSString *pathWithoutTransparency = [documentsPath stringByAppendingPathComponent:@"image-but-no-transparency.png"];
    NSData   *data                    = UIImagePNGRepresentation(finalImage);
    [data writeToFile:pathWithoutTransparency atomically:YES];   // save it so I can check out the file in Photoshop

    // In iOS 7, the following imageview does not honor the transparency

    self.imageView2.image = [UIImage imageWithData:data];        // this does not work in iOS 7

    // but, if I round-trip the original image through `drawInRect` one final time,
    // the transparency works

    UIGraphicsBeginImageContextWithOptions(finalImage.size, NO, 1.0);
    [finalImage drawInRect:CGRectMake(0, 0, finalImage.size.width, finalImage.size.height)];
    UIImage *anotherRendition = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    data = UIImagePNGRepresentation(anotherRendition);
    NSString *pathWithTransparency = [documentsPath stringByAppendingPathComponent:@"image-with-transparancy.png"];
    [data writeToFile:pathWithTransparency atomically:YES];

    // But this image is fine

    self.imageView3.image = [UIImage imageWithContentsOfFile:pathWithTransparency];   // this does work

    return anotherRendition;
}

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