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

A Swift implementation of bluebamboo's answer:

func tintedImage(_ image: NSImage, tint: NSColor) -> NSImage {
    guard let tinted = image.copy() as? NSImage else { return image }
    tinted.lockFocus()
    tint.set()

    let imageRect = NSRect(origin: NSZeroPoint, size: image.size)
    NSRectFillUsingOperation(imageRect, .sourceAtop)

    tinted.unlockFocus()
    return tinted
}

Answer 2

I wanted to tint an image with a tint color that had alpha without seeing the original colors of the image show through. Here's how you can do that:

extension NSImage {
    func tinting(with tintColor: NSColor) -> NSImage {
        guard let cgImage = self.cgImage(forProposedRect: nil, context: nil, hints: nil) else { return self }

        return NSImage(size: size, flipped: false) { bounds in
            guard let context = NSGraphicsContext.current?.cgContext else { return false }

            tintColor.set()
            context.clip(to: bounds, mask: cgImage)
            context.fill(bounds)

            return true
        }
    }
}

Answer 3

Swift version in form of Extension :

extension NSImage {
    func tintedImageWithColor(color:NSColor) -> NSImage {
        let size        = self.size
        let imageBounds = NSMakeRect(0, 0, size.width, size.height)
        let copiedImage = self.copy() as! NSImage

        copiedImage.lockFocus()
        color.set()
        NSRectFillUsingOperation(imageBounds, .CompositeSourceIn)
        copiedImage.unlockFocus()

        return copiedImage
    }
}

Answer 4

- (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];
}

Answer 5

The CIMultiplyCompositing filter is definitely the way to do this. If it's crashing, can you post a stack trace? I use CIFilters heavily and don't have crashing issues.

//assume inputImage is the greyscale CIImage you want to tint

CIImage* outputImage = nil;

//create some green
CIFilter* greenGenerator = [CIFilter filterWithName:@"CIConstantColorGenerator"];
CIColor* green = [CIColor colorWithRed:0.30 green:0.596 blue:0.172];
[greenGenerator setValue:green forKey:@"inputColor"];
CIImage* greenImage = [greenGenerator valueForKey:@"outputImage"];

//apply a multiply filter
CIFilter* filter = [CIFilter filterWithName:@"CIMultiplyCompositing"];
[filter setValue:greenImage forKey:@"inputImage"];
[filter setValue:inputImage forKey:@"inputBackgroundImage"];
outputImage = [filter valueForKey:@"outputImage"];

[outputImage drawAtPoint:NSZeroPoint fromRect:NSRectFromCGRect([outputImage extent]) operation:NSCompositeCopy fraction:1.0];

Answer 6

Swift 5 version that also handles the alpha component of the tint color.

I use this to support dark mode with multiple icon states by converting template icons to different colors and transparency levels. For example, you could pass NSColor(white: 0, alpha: 0.5) to get a dimmed version of an icon for light mode, and NSColor(white: 1, alpha: 0.5) to get a dimmed version for dark mode.

func tintedImage(_ image: NSImage, color: NSColor) -> NSImage {
    let newImage = NSImage(size: image.size)
    newImage.lockFocus()

    // Draw with specified transparency
    let imageRect = NSRect(origin: .zero, size: image.size)
    image.draw(in: imageRect, from: imageRect, operation: .sourceOver, fraction: color.alphaComponent)

    // Tint with color
    color.withAlphaComponent(1).set()
    imageRect.fill(using: .sourceAtop)

    newImage.unlockFocus()
    return newImage
}