如何使一个颜色透明的UIImage？ [英] How to make one color transparent on a UIImage?

问题描述

在我的iPhone应用程序，我有一个UIImage实例。我想得到一个衍生的UIImage，它是第一个UIImage的结果，其中的一种颜色（例如洋红色）是透明的。

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   - （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 * contributedimage = [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; 
} 
  

上面的代码被测试，我改变绿色为红色面具

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?

解决方案

-(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;
}   

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

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