将RGB图像转换为灰度图像，并将灰度图像转换为RGB图像? [英] Convert RGB Image to Grayscale and Grayscale to RGB Image?

问题描述

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.请帮忙.预先感谢.

I have successfully converted an Image to Grayscale, I want to revert the Grayscale Image back to RGB Image. Please help. Thanks in advance.

-(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;
}

推荐答案

要回答有关转换的问题，您的灰度代码是

To answer the question about converting, your code for grayscale:

uint8_t gray = (uint8_t) ((30 * rgbaPixel[RED] + 59 * rgbaPixel[GREEN] + 11 * rgbaPixel[BLUE]) / 100);

建立关系:

S = 0.3R + 0.59G + 0.11B

从RGB转到S涉及用一个方程式(fine！)解决一个未知数(S). 转换就像在给定一个不可能的方程式的情况下尝试尝试三个未知数(RGB).

Go go from RGB to S involves solving for one unknown (S) with one equation (fine!). To convert back is like trying for three unknowns (RGB) given one equation which isn't possible.

进行灰度着色的一种方法是将灰度视为强度，然后进行设置

One hack to doing a grayscale colorisation is to consider grayscale as just intensity, and set

R = G = B = S-但这不会正确(显然)恢复您的颜色. 简而言之，转换为灰度是不可逆的功能，就像对数字进行平方(是正数还是负数)一样-信息丢失并且无法检索.

R = G = B = S - but this isn't going to restore your colors correctly (obviously). 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.

这篇关于将RGB图像转换为灰度图像，并将灰度图像转换为RGB图像?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！