问题描述
当我使用以下代码时：
UIImage *image=[UIImage imageNamed:@"loginf1.png"];
CGImageRef rawImageRef=image.CGImage;
const float colorMasking[6] = {222, 255, 222, 255, 222, 255};
CGImageRef maskedImageRef=CGImageCreateWithMaskingColors(rawImageRef, colorMasking);
maskedImageRef 总是为零。为什么会这样，我该怎么做才能纠正这个问题？
maskedImageRefis always nil. Why is this, and what can I do to correct this?
推荐答案
我遇到了同样的问题。您正在创建的 CGImageRef 每个像素只有6个字节，字节没有alpha通道。掩蔽函数需要一个 CGImageRef ，每个像素有8个字节，其中只有6个使用，没有alpha通道。至少，我认为这就是造成它的原因。
I had the same problem. The CGImageRef you are creating has only 6 bytes for each pixel with byte with no alpha channel. The masking function needs a CGImageRef with 8 bytes for each pixel, only 6 of them used, with no alpha channel. At least, I think this is what's causing it.
无论如何，通过创建位图上下文来修复它，将图像绘制到该位图上下文，然后从 CGBitmapContextCreateImage 获取CGImageRef。
Anyway, fix it by creating a bitmap context, drawing your image to that bitmap context, then getting your CGImageRef from CGBitmapContextCreateImage.
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