[英]Convert RGB Image to Grayscale and Grayscale to RGB Image?
I have successfully converted an Image to Grayscale, I want to revert the Grayscale Image back to RGB Image. 我已成功将图像转换为灰度图像,我想将灰度图像恢复为RGB图像。 Please help.
请帮忙。 Thanks in advance.
提前致谢。
-(UIImage *) toGrayscale
{
const int RED = 1;
const int GREEN = 2;
const int BLUE = 3;
Create image rectangle with current image width/height
CGRect imageRect = CGRectMake(0, 0, self.size.width * self.scale, self.size.height * self.scale);
int width = imageRect.size.width;
int height = imageRect.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];
// convert to grayscale using recommended method: http://en.wikipedia.org/wiki/Grayscale#Converting_color_to_grayscale
uint8_t gray = (uint8_t) ((30 * rgbaPixel[RED] + 59 * rgbaPixel[GREEN] + 11 * rgbaPixel[BLUE]) / 100);
// set the pixels to gray
rgbaPixel[RED] = gray;
rgbaPixel[GREEN] = gray;
rgbaPixel[BLUE] = gray;
}
}
// 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
scale:self.scale
orientation:UIImageOrientationUp];
// we're done with image now too
CGImageRelease(image);
return resultUIImage;
}
To answer the question about converting , your code for grayscale: 要回答有关conversion的问题,您的灰度代码:
uint8_t gray = (uint8_t) ((30 * rgbaPixel[RED] + 59 * rgbaPixel[GREEN] + 11 * rgbaPixel[BLUE]) / 100);
gives the relationship: 给出关系:
S = 0.3R + 0.59G + 0.11B
Go go from RGB
to S
involves solving for one unknown ( S
) with one equation (fine!). 从
RGB
转到S
涉及用一个方程式(fine!)解决一个未知数( S
)。 To convert back is like trying for three unknowns ( RGB
) given one equation which isn't possible. 转换回来就像在给定一个方程式的情况下尝试尝试三个未知数(
RGB
)一样。
One hack to doing a grayscale colorisation is to consider grayscale as just intensity, and set 进行灰度着色的一种方法是将灰度视为强度,然后设置
R = G = B = S
- but this isn't going to restore your colors correctly (obviously). R = G = B = S
但这不会正确(显然)恢复您的颜色。 So in short, conversion to grayscale is an irreversible function, like squaring a number (was it positive or negative?) - information is lost and can't be retrieved. 简而言之,转换为灰度是不可逆的功能,就像对数字求平方(它是正数还是负数)一样-信息丢失并且无法检索。
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