iphone - iOS 灰度/黑白

Question

我遇到了一些将 UIImage 更改为灰度的代码的问题。它可以在 iPhone/iPod 上正常工作，但在 iPad 上，任何已经绘制的内容都会在此过程中被拉伸(stretch)和扭曲。

它有时也只在 iPad 上崩溃就行了
imageRef = CGBitmapContextCreateImage (ctx);

这是代码:

CGContextRef ctx;
CGImageRef imageRef = [self.drawImage.image CGImage];
NSUInteger width = CGImageGetWidth(imageRef);
NSUInteger height = CGImageGetHeight(imageRef);
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
unsigned char *rawData = malloc(height * width * 4);
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);

int byteIndex = 0;
int grayScale;

for(int ii = 0 ; ii < width * height ; ++ii)
{
    grayScale = (rawData[byteIndex] + rawData[byteIndex + 1] + rawData[byteIndex + 2]) / 3;

    rawData[byteIndex] = (char)grayScale;
    rawData[byteIndex+1] = (char)grayScale;
    rawData[byteIndex+2] = (char)grayScale;
    //rawData[byteIndex+3] = 255;

    byteIndex += 4;
}


ctx = CGBitmapContextCreate(rawData,
                            CGImageGetWidth( imageRef ),
                            CGImageGetHeight( imageRef ),
                            8,
                            CGImageGetBytesPerRow( imageRef ),
                            CGImageGetColorSpace( imageRef ),
                            kCGImageAlphaPremultipliedLast ); 

imageRef = CGBitmapContextCreateImage (ctx);
UIImage* rawImage = [UIImage imageWithCGImage:imageRef];  

CGContextRelease(ctx);  

self.drawImage.image = rawImage;  

free(rawData);

Answer 1

考虑利用 CIColorMonochrome iOS 6 中可用的过滤器。

void ToMonochrome()
{
    var mono = new CIColorMonochrome();
    mono.Color = CIColor.FromRgb(1, 1, 1);
    mono.Intensity = 1.0f;
    var uiImage = new UIImage("Images/photo.jpg");
    mono.Image = CIImage.FromCGImage(uiImage.CGImage);
    DisplayFilterOutput(mono, ImageView);
}

static void DisplayFilterOutput(CIFilter filter, UIImageView imageView)
{
    CIImage output = filter.OutputImage;
    if (output == null)
        return;
    var context = CIContext.FromOptions(null);
    var renderedImage = context.CreateCGImage(output, output.Extent);
    var finalImage = new UIImage(renderedImage);
    imageView.Image = finalImage;
}