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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