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//
// UIImage+ColorMasking.m
// Cartographic
//
// Created by Starla Insigna on 8/22/11.
// Copyright 2011 Four Island. All rights reserved.
//
#import "UIImage+ColorMasking.h"
@implementation UIImage (ColorMasking)
typedef enum {
ALPHA = 0,
BLUE = 1,
GREEN = 2,
RED = 3
} PIXELS;
- (UIImage *)opaqueMaskFromWhiteImage
{
CGSize size = [self size];
int width = size.width;
int height = size.height;
// the pixels will be painted to this array
uint32_t *pixels = (uint32_t *) malloc(width * height * sizeof(uint32_t));
// clear the pixels so any transparency is preserved
memset(pixels, 0, width * height * sizeof(uint32_t));
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
// create a context with RGBA pixels
CGContextRef context = CGBitmapContextCreate(pixels, width, height, 8, width * sizeof(uint32_t), colorSpace,
kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedLast);
// paint the bitmap to our context which will fill in the pixels array
CGContextDrawImage(context, CGRectMake(0, 0, width, height), [self CGImage]);
for(int y = 0; y < height; y++) {
for(int x = 0; x < width; x++) {
uint8_t *rgbaPixel = (uint8_t *) &pixels[y * width + x];
if ((rgbaPixel[RED] == 255) && (rgbaPixel[GREEN] == 255) && (rgbaPixel[BLUE] == 255) && (rgbaPixel[ALPHA] == 255))
{
rgbaPixel[RED] = 255;
rgbaPixel[GREEN] = 255;
rgbaPixel[BLUE] = 255;
rgbaPixel[ALPHA] = 255;
} else {
rgbaPixel[RED] = 0;
rgbaPixel[GREEN] = 0;
rgbaPixel[BLUE] = 0;
rgbaPixel[ALPHA] = 0;
}
}
}
// create a new CGImageRef from our context with the modified pixels
CGImageRef image = CGBitmapContextCreateImage(context);
// we're done with the context, color space, and pixels
CGContextRelease(context);
CGColorSpaceRelease(colorSpace);
free(pixels);
// make a new UIImage to return
UIImage *resultUIImage = [UIImage imageWithCGImage:image];
// we're done with image now too
CGImageRelease(image);
return resultUIImage;
}
@end
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