iOS 获取图片某一点的颜色对象（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,

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

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