iPhone拍摄灰度截图？

Question

I'm wondering if there is a SIMPLE way to take a Grayscale screenshot, i know i can take color screenshot like this:

    UIGraphicsBeginImageContext(self.view.bounds.size);
    [self.view.layer renderInContext:UIGraphicsGetCurrentContext()];
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    NSData *data = UIImagePNGRepresentation(image);

now what i need to add in these lines of code to make the UIImage Grayscaled? thank you for reading.

Answer 1

Just convert your image to gray scale. Read this post. Good luck.

Here is the method:d

#pragma mark -
#pragma mark Grayscale

- (UIImage *)convertImageToGrayScale:(UIImage *)image
{
    // Create image rectangle with current image width/height
    CGRect imageRect = CGRectMake(0, 0, image.size.width, image.size.height);

    // Grayscale color space
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray();

    // Create bitmap content with current image size and grayscale colorspace
    CGContextRef context = CGBitmapContextCreate(nil, image.size.width, image.size.height, 8, 0, colorSpace, kCGImageAlphaNone);

    // Draw image into current context, with specified rectangle
    // using previously defined context (with grayscale colorspace)
    CGContextDrawImage(context, imageRect, [image CGImage]);

    // Create bitmap image info from pixel data in current context
    CGImageRef imageRef = CGBitmapContextCreateImage(context);

    // Create a new UIImage object  
    UIImage *newImage = [UIImage imageWithCGImage:imageRef];

    // Release colorspace, context and bitmap information
    CGColorSpaceRelease(colorSpace);
    CGContextRelease(context);
    CFRelease(imageRef);

    // Return the new grayscale image
    return newImage;
}

Answer 2

Based on Cam's code with the ability to deal with the scale for Retina displays.

- (UIImage *) toGrayscale 
{
// 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
        uint32_t gray = 0.3 * rgbaPixel[RED] + 0.59 * rgbaPixel[GREEN] + 0.11 * rgbaPixel[BLUE];

        // 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;
}