如何在 UIImage 上使一种颜色透明? [英] How to make one color transparent on a UIImage?

问题描述

在我的 iPhone 应用程序上，我有一个 UIImage 实例.我想获得一个派生的 UIImage，它是第一个 UIImage 的结果，其中一个颜色(例如洋红色)被设为透明.我该怎么做?

On my iPhone app I have a UIImage instance. I want to get a derived a UIImage that is the result of the first UIImage where one of its colors (e.g. magenta) is made transparent. How can I do this?

推荐答案

-(void)changeColor
{
    UIImage *temp23=[UIImage imageNamed:@"leaf.png"];
    CGImageRef ref1=[self createMask:temp23];
    const float colorMasking[6] = {1.0, 2.0, 1.0, 1.0, 1.0, 1.0};
    CGImageRef New=CGImageCreateWithMaskingColors(ref1, colorMasking);
    UIImage *resultedimage=[UIImage imageWithCGImage:New];
}

-(CGImageRef)createMask:(UIImage*)temp
{
    CGImageRef ref=temp.CGImage;
    int mWidth=CGImageGetWidth(ref);
    int mHeight=CGImageGetHeight(ref);
    int count=mWidth*mHeight*4;
    void *bufferdata=malloc(count);

    CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB();
    CGBitmapInfo bitmapInfo = kCGBitmapByteOrderDefault;
    CGColorRenderingIntent renderingIntent = kCGRenderingIntentDefault;

    CGContextRef cgctx = CGBitmapContextCreate (bufferdata,mWidth,mHeight, 8,mWidth*4, colorSpaceRef, kCGImageAlphaPremultipliedFirst); 

    CGRect rect = {0,0,mWidth,mHeight};
    CGContextDrawImage(cgctx, rect, ref); 
    bufferdata = CGBitmapContextGetData (cgctx);

    CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, bufferdata, mWidth*mHeight*4, NULL);
    CGImageRef savedimageref = CGImageCreate(mWidth,mHeight, 8, 32, mWidth*4, colorSpaceRef, bitmapInfo,provider , NULL, NO, renderingIntent);
    CFRelease(colorSpaceRef);
    return savedimageref;
}   

上面的代码经过测试，我通过使用掩码将绿色更改为红色

The above code is tested and I changed the green color to red color by using mask

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