image处理相关

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image做遮罩mask

原理性的东西请参考Quartz 2D Programming Guide - Bitmap Images and Image Masks，也可以参考iOS绘图教程

请参考:

How to Mask an Image
Mask and crop an image
【iPhone App開發】How to clip a UIImage?

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实现方式是：

- (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 masked = CGImageCreateWithMask([image CGImage], mask);    return [UIImage imageWithCGImage:masked];}

另一种方式会使用到

CGContextClipToMask(context, self.bounds, mask);

例如iOS Programming Recipe 24: Creating a Mask for Clipping Drawings例子中，利用mask来实现一个渐变的圆圈

-(void)drawEllipseWithGradient:(CGContextRef)context{    CGContextSaveGState(context);    //UIGraphicsBeginImageContextWith(self.frame.size);    UIGraphicsBeginImageContextWithOptions((self.frame.size), NO, 0.0);    CGContextRef newContext = UIGraphicsGetCurrentContext();      //Set color of current context   [[UIColor blackColor] set];   //Draw ellipse &lt;- I know we’re drawing a circle, but a circle is just a special ellipse.   CGRect ellipseRect = CGRectMake(110.0f, 200.0f, 100.0f, 100.0f);   CGContextFillEllipseInRect(newContext, ellipseRect);    CGImageRef mask = CGBitmapContextCreateImage(UIGraphicsGetCurrentContext());   UIGraphicsEndImageContext();    CGContextClipToMask(context, self.bounds, mask);    [self drawGradient:context];    CGImageRelease(mask);    CGContextRestoreGState(context);}

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CoreGraphic 遮色片應用中的例子也一样

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UIImage *iconImage = [UIImage imageNamed:@"logo.png"];UIImage *maskImage = [UIImage imageNamed:@"mask.png"];UIGraphicsBeginImageContext(iconImage.size);//設定參考範圍CGContextRef context = UIGraphicsGetCurrentContext();CGContextScaleCTM(context, 1, -1);CGRect region = CGRectMake(0, 0, iconImage.size.width, iconImage.size.height);CGContextTranslateCTM(context, 0, -region.size.height);//將context做遮罩範圍的切割再drawCGContextClipToMask(context, region, maskImage.CGImage);CGContextDrawImage(context, region, iconImage.CGImage);//將影像指定給imageViewimageView.image = UIGraphicsGetImageFromCurrentImageContext();UIGraphicsEndImageContext();

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