Get pixel data from CGImageRef

gistfile1.txt

- (void)testGetPixelDataFromCGImageRefExample {
    
    UIImage *image = [self loadImage];
    [self rawDataCopyWithImage:image];
    [self rawDataDrawWithImage:image];
}

- (void)rawDataCopyWithImage:(UIImage*)image
{
    CGImageRef  imageRef = image.CGImage;
    CGDataProviderRef dataProvider = CGImageGetDataProvider(imageRef);
    
    __block CFDataRef dataRef;
    dataRef = CGDataProviderCopyData(dataProvider);
    
    UInt8* buffer = (UInt8*)CFDataGetBytePtr(dataRef);
    size_t bytesPerRow = CGImageGetBytesPerRow(imageRef);

    [self printData:buffer width:image.size.width height:image.size.height bytesPerRow:bytesPerRow];
    
    CFRelease(dataRef);
}

- (void)rawDataDrawWithImage:(UIImage*)image
{
    CGImageRef imageRef = [image CGImage];
    NSUInteger width = CGImageGetWidth(imageRef);
    NSUInteger height = CGImageGetHeight(imageRef);
    
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    unsigned char *rawData = (unsigned char*) calloc(height * width * 4, sizeof(unsigned char));
    NSUInteger bytesPerPixel = 4;
    NSUInteger bytesPerRow = bytesPerPixel * width;
    NSUInteger bitsPerComponent = 8;
    CGContextRef context = CGBitmapContextCreate(rawData, width, height,
                                                 bitsPerComponent, bytesPerRow, colorSpace,
                                                 kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
    CGColorSpaceRelease(colorSpace);
    
    CGContextDrawImage(context, CGRectMake(0, 0, width, height), imageRef);
    CGContextRelease(context);
    
    [self printData:rawData width:width height:height bytesPerRow:bytesPerRow];
    
    free(rawData);
}

- (void)printData:(UInt8*)data width:(NSInteger)width height:(NSInteger)height bytesPerRow:(size_t)bytesPerRow
{
    for (NSInteger x=0; x<width; x++)
    {
        for (NSInteger y=0; y<height; y++)
        {
            // ピクセルのポインタを取得する
            UInt8*  pixelPtr = data + (int)(y) * bytesPerRow + (int)(x) * 4;
            
            // 色情報を取得する
            UInt8 r = *(pixelPtr + 2);  // 赤
            UInt8 g = *(pixelPtr + 1);  // 緑
            UInt8 b = *(pixelPtr + 0);  // 青
            
            NSLog(@"x:%ld y:%ld R:%d G:%d B:%d", (long)x, (long)y, r, g, b);
        }
    }
}

- (UIImage*)loadImage
{
    return [UIImage imageNamed:@"colorpattern.jpg"];
}