iOS 擷取圖片某一點的顏色對象（UIColor*）。

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- (UIColor *)colorAtPixel:(CGPoint)point {

    // Cancel if point is outside image coordinates

    if (!CGRectContainsPoint(CGRectMake(0.0f,0.0f, self.size.width,self.size.height), point)) {

        return nil;

    }

    NSInteger pointX = trunc(point.x);

    NSInteger pointY = trunc(point.y);

    CGImageRef cgImage = self.CGImage;

    NSUInteger width =self.size.width;

    NSUInteger height =self.size.height;

    CGColorSpaceRef colorSpace =CGColorSpaceCreateDeviceRGB();

    int bytesPerPixel = 4;

    int bytesPerRow = bytesPerPixel * 1;

    NSUInteger bitsPerComponent = 8;

    unsigned char pixelData[4] = {0, 0, 0, 0 };

    CGContextRef context = CGBitmapContextCreate(pixelData, 

                                                 1,

                                                 1,

                                                 bitsPerComponent, 

                                                 bytesPerRow, 

                                                 colorSpace,

                                                 kCGImageAlphaPremultipliedLast |kCGBitmapByteOrder32Big);

    CGColorSpaceRelease(colorSpace);

    CGContextSetBlendMode(context,kCGBlendModeCopy);

    // Draw the pixel we are interested in onto the bitmap context

    CGContextTranslateCTM(context, -pointX, pointY-(CGFloat)height);

    CGContextDrawImage(context, CGRectMake(0.0f, 0.0f, (CGFloat)width, (CGFloat)height), cgImage);

    CGContextRelease(context);

    

    // Convert color values [0..255] to floats [0.0..1.0]

    CGFloat red   = (CGFloat)pixelData[0] /255.0f;

    CGFloat green = (CGFloat)pixelData[1] /255.0f;

    CGFloat blue  = (CGFloat)pixelData[2] /255.0f;

    CGFloat alpha = (CGFloat)pixelData[3] /255.0f;

    return [UIColorcolorWithRed:red green:greenblue:blue alpha:alpha];

}

UIImage+ColorAtPixel.h #import <UIKit/UIKit.h>/* A category on UIImage that enables you to query the color value of arbitrary  pixels of the image. */@interface UIImage (ColorAtPixel)- (UIColor *)colorAtPixel:(CGPoint)point;@end#import <CoreGraphics/CoreGraphics.h>#import "UIImage+ColorAtPixel.h"@implementation UIImage (ColorAtPixel)- (UIColor *)colorAtPixel:(CGPoint)point {    // Cancel if point is outside image coordinates    if (!CGRectContainsPoint(CGRectMake(0.0f, 0.0f, self.size.width, self.size.height), point)) {        return nil;    }    NSInteger pointX = trunc(point.x);    NSInteger pointY = trunc(point.y);    CGImageRef cgImage = self.CGImage;    NSUInteger width = self.size.width;    NSUInteger height = self.size.height;    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();    int bytesPerPixel = 4;    int bytesPerRow = bytesPerPixel * 1;    NSUInteger bitsPerComponent = 8;    unsigned char pixelData[4] = { 0, 0, 0, 0 };    CGContextRef context = CGBitmapContextCreate(pixelData,                                                  1,                                                 1,                                                 bitsPerComponent,                                                  bytesPerRow,                                                  colorSpace,                                                 kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);    CGColorSpaceRelease(colorSpace);    CGContextSetBlendMode(context, kCGBlendModeCopy);    // Draw the pixel we are interested in onto the bitmap context    CGContextTranslateCTM(context, -pointX, pointY-(CGFloat)height);    CGContextDrawImage(context, CGRectMake(0.0f, 0.0f, (CGFloat)width, (CGFloat)height), cgImage);    CGContextRelease(context);        // Convert color values [0..255] to floats [0.0..1.0]    CGFloat red   = (CGFloat)pixelData[0] / 255.0f;    CGFloat green = (CGFloat)pixelData[1] / 255.0f;    CGFloat blue  = (CGFloat)pixelData[2] / 255.0f;    CGFloat alpha = (CGFloat)pixelData[3] / 255.0f;    return [UIColor colorWithRed:red green:green blue:blue alpha:alpha];}@end