Tinting a grayscale NSImage (or CIImage)

Question

I have a grayscale image which I want to use for drawing Cocoa controls. The image has various levels of gray. Where it is darkest, I want it to draw a specified tint color dark

Answer 1

- (NSImage *)imageTintedWithColor:(NSColor *)tint 
{
    if (tint != nil) {
        NSSize size = [self size];
        NSRect bounds = { NSZeroPoint, size };
        NSImage *tintedImage = [[NSImage alloc] initWithSize:size];

        [tintedImage lockFocus];

        CIFilter *colorGenerator = [CIFilter filterWithName:@"CIConstantColorGenerator"];
        CIColor *color = [[[CIColor alloc] initWithColor:tint] autorelease];

        [colorGenerator setValue:color forKey:@"inputColor"];

        CIFilter *monochromeFilter = [CIFilter filterWithName:@"CIColorMonochrome"];
        CIImage *baseImage = [CIImage imageWithData:[self TIFFRepresentation]];

        [monochromeFilter setValue:baseImage forKey:@"inputImage"];     
        [monochromeFilter setValue:[CIColor colorWithRed:0.75 green:0.75 blue:0.75] forKey:@"inputColor"];
        [monochromeFilter setValue:[NSNumber numberWithFloat:1.0] forKey:@"inputIntensity"];

        CIFilter *compositingFilter = [CIFilter filterWithName:@"CIMultiplyCompositing"];

        [compositingFilter setValue:[colorGenerator valueForKey:@"outputImage"] forKey:@"inputImage"];
        [compositingFilter setValue:[monochromeFilter valueForKey:@"outputImage"] forKey:@"inputBackgroundImage"];

        CIImage *outputImage = [compositingFilter valueForKey:@"outputImage"];

        [outputImage drawAtPoint:NSZeroPoint
                        fromRect:bounds
                       operation:NSCompositeCopy
                        fraction:1.0];

        [tintedImage unlockFocus];  

        return [tintedImage autorelease];
    }
    else {
        return [[self copy] autorelease];
    }
}

- (NSImage*)imageCroppedToRect:(NSRect)rect
{
    NSPoint point = { -rect.origin.x, -rect.origin.y };
    NSImage *croppedImage = [[NSImage alloc] initWithSize:rect.size];

    [croppedImage lockFocus];
    {
        [self compositeToPoint:point operation:NSCompositeCopy];
    }
    [croppedImage unlockFocus];

    return [croppedImage autorelease];
}