Question

I’m just starting to learn about Quartz Composer and the first thing I would like to create is a composition that could eventually be used in a Cocoa application which would accept a black and white image and two NSColor’s and change the black pixels to NSColor #1 and the white pixels to NSColor #2.

I’ve spent some time playing with QC, but cannot seem to figure out how to put all of the pieces together.

About the only thing I have figured out is that I need to use the Image Filter template and I do see there is a Image Pixel patch that can get pixels from an image…however, I don’t see a patch to set a pixel. It also seems possible the Pixellate patch might be necessary…although, I shouldn’t have to worry about it producing an image with infinite dimensions since my source images will only be fixed size PNG images.

Answer 1

Take a look at the False Color patch — it takes an image and remaps it with a pair of colors.

In fact, since the False Color patch is just a wrapper around the Core Image filter with the same name (CIFalseColor), you could do this without involving Quartz Composer at all — just set up and apply a CIFilter instance to your NSImage.

Edit — or write your own Core Image filter, starting with something like this:

kernel vec4 remapBasedOnRed(sampler image,__color colorForDark,__color colorForLight)
{
    return mix(colorForDark,colorForLight,sample(image, samplerCoord(image)).r);
}

…which takes the brightness of the red channel of the input image (sample(image, samplerCoord(image)).r), and uses it as a coefficient for linear interpolation between colorForDark and colorForLight.