问如何改变UIImage/UIImageView单个像素的颜色

EN

@interface UIImageView (PointConversionCatagory)

@property (nonatomic, readonly) CGAffineTransform viewToImageTransform;
@property (nonatomic, readonly) CGAffineTransform imageToViewTransform;

@end

@implementation UIImageView (PointConversionCatagory)

-(CGAffineTransform) viewToImageTransform {

    UIViewContentMode contentMode = self.contentMode;

    // failure conditions. If any of these are met – return the identity transform
    if (!self.image || self.frame.size.width == 0 || self.frame.size.height == 0 ||
        (contentMode != UIViewContentModeScaleToFill && contentMode != UIViewContentModeScaleAspectFill && contentMode != UIViewContentModeScaleAspectFit)) {
        return CGAffineTransformIdentity;
    }

    // the width and height ratios
    CGFloat rWidth = self.image.size.width/self.frame.size.width;
    CGFloat rHeight = self.image.size.height/self.frame.size.height;

    // whether the image will be scaled according to width
    BOOL imageWiderThanView = rWidth > rHeight;

    if (contentMode == UIViewContentModeScaleAspectFit || contentMode == UIViewContentModeScaleAspectFill) {

        // The ratio to scale both the x and y axis by
        CGFloat ratio = ((imageWiderThanView && contentMode == UIViewContentModeScaleAspectFit) || (!imageWiderThanView && contentMode == UIViewContentModeScaleAspectFill)) ? rWidth:rHeight;

        // The x-offset of the inner rect as it gets centered
        CGFloat xOffset = (self.image.size.width-(self.frame.size.width*ratio))*0.5;

        // The y-offset of the inner rect as it gets centered
        CGFloat yOffset = (self.image.size.height-(self.frame.size.height*ratio))*0.5;

        return CGAffineTransformConcat(CGAffineTransformMakeScale(ratio, ratio), CGAffineTransformMakeTranslation(xOffset, yOffset));
    } else {
        return CGAffineTransformMakeScale(rWidth, rHeight);
    }
}

-(CGAffineTransform) imageToViewTransform {
    return CGAffineTransformInvert(self.viewToImageTransform);
}

@end

UITapGestureRecognizer *tapGesture = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(imageViewWasTapped:)];
tapGesture.numberOfTapsRequired = 1;
[imageView addGestureRecognizer:tapGesture];

...

-(void) imageViewWasTapped:(UIGestureRecognizer*)tapGesture {

    if (!imageView.image) {
        return;
    }

    // get the pixel position
    CGPoint pt = CGPointApplyAffineTransform([tapGesture locationInView:imageView], imageView.viewToImageTransform);
    PixelPosition pixelPos = {(NSInteger)floor(pt.x), (NSInteger)floor(pt.y)};

    // replace image with new image, with the pixel replaced
    imageView.image = [imageView.image imageWithPixel:pixelPos replacedByColor:[UIColor colorWithRed:0 green:1 blue:1 alpha:1.0]];
}

/// A simple struct to represent the position of a pixel
struct PixelPosition {
    NSInteger x;
    NSInteger y;
};

typedef struct PixelPosition PixelPosition;

@interface UIImage (UIImagePixelManipulationCatagory)

@end

@implementation UIImage (UIImagePixelManipulationCatagory)

-(UIImage*) imageWithPixel:(PixelPosition)pixelPosition replacedByColor:(UIColor*)color {

    // components of replacement color – in a 255 UInt8 format (fairly standard bitmap format)
    const CGFloat* colorComponents = CGColorGetComponents(color.CGColor);
    UInt8* color255Components = calloc(sizeof(UInt8), 4);
    for (int i = 0; i < 4; i++) color255Components[i] = (UInt8)round(colorComponents[i]*255.0);

    // raw image reference
    CGImageRef rawImage = self.CGImage;

    // image attributes
    size_t width = CGImageGetWidth(rawImage);
    size_t height = CGImageGetHeight(rawImage);
    CGRect rect = {CGPointZero, {width, height}};

    // image format
    size_t bitsPerComponent = 8;
    size_t bytesPerRow = width*4;

    // the bitmap info
    CGBitmapInfo bitmapInfo = kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big;

    // data pointer – stores an array of the pixel components. For example (r0, b0, g0, a0, r1, g1, b1, a1 .... rn, gn, bn, an)
    UInt8* data = calloc(bytesPerRow, height);

    // get new RGB color space
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

    // create bitmap context
    CGContextRef ctx = CGBitmapContextCreate(data, width, height, bitsPerComponent, bytesPerRow, colorSpace, bitmapInfo);

    // draw image into context (populating the data array while doing so)
    CGContextDrawImage(ctx, rect, rawImage);

    // get the index of the pixel (4 components times the x position plus the y position times the row width)
    NSInteger pixelIndex = 4*(pixelPosition.x+(pixelPosition.y*width));

    // set the pixel components to the color components
    data[pixelIndex] = color255Components[0]; // r
    data[pixelIndex+1] = color255Components[1]; // g
    data[pixelIndex+2] = color255Components[2]; // b
    data[pixelIndex+3] = color255Components[3]; // a

    // get image from context
    CGImageRef img = CGBitmapContextCreateImage(ctx);

    // clean up
    free(color255Components);
    CGContextRelease(ctx);
    CGColorSpaceRelease(colorSpace);
    free(data);

    UIImage* returnImage = [UIImage imageWithCGImage:img];
    CGImageRelease(img);

    return returnImage;
}

@end

// get the index of the pixel (4 components times the x position plus the y position times the row width)
NSInteger pixelIndex = 4*(pixelPosition.x+(pixelPosition.y*width));

// set the pixel components to the color components
data[pixelIndex] = color255Components[0]; // r
data[pixelIndex+1] = color255Components[1]; // g
data[pixelIndex+2] = color255Components[2]; // b
data[pixelIndex+3] = color255Components[3]; // a

UIImage *originalImage = [UIImage imageNamed:@"something"];

CGSize size = originalImage.size;

UIGraphicsBeginImageContext(size);

[originalImage drawInRect:CGRectMake(0, 0, size.width, size.height)];

// myColor is an instance of UIColor
[myColor setFill];
UIRectFill(CGRectMake(someX, someY, 1, 1);

UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();

UIGraphicsEndImageContext();