- (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];
}
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