Skip to content

Instantly share code, notes, and snippets.

@fabb

fabb/UIImage+Colorize.swift

Created December 18, 2015 13:00
Show Gist options
  • Save fabb/007d30ba0759de9be8a3 to your computer and use it in GitHub Desktop.
Save fabb/007d30ba0759de9be8a3 to your computer and use it in GitHub Desktop.
Download ZIP

Revisions

  1. fabb revised this gist Dec 18, 2015. 1 changed file with 2 additions and 0 deletions.
    2 changes: 2 additions & 0 deletions UIImage+Colorize.swift
    View file
    Original file line number Diff line number Diff line change
    @@ -1,3 +1,5 @@
    import UIKit

    extension UIImage {

    // colorize image with given tint color
  2. fabb renamed this gist Dec 18, 2015. 1 changed file with 0 additions and 0 deletions.
    0 UIImage+Colorize → UIImage+Colorize.swift
    View file
    File renamed without changes.
  3. fabb created this gist Dec 18, 2015.
    66 changes: 66 additions & 0 deletions UIImage+Colorize
    View file
    Original file line number Diff line number Diff line change
    @@ -0,0 +1,66 @@
    extension UIImage {

    // colorize image with given tint color
    // this is similar to Photoshop's "Color" layer blend mode
    // this is perfect for non-greyscale source images, and images that have both highlights and shadows that should be preserved
    // white will stay white and black will stay black as the lightness of the image is preserved
    func tint(tintColor: UIColor) -> UIImage {

    return modifiedImage { context, rect in
    // draw black background - workaround to preserve color of partially transparent pixels
    CGContextSetBlendMode(context, .Normal)
    UIColor.blackColor().setFill()
    CGContextFillRect(context, rect)

    // draw original image
    CGContextSetBlendMode(context, .Normal)
    CGContextDrawImage(context, rect, self.CGImage)

    // tint image (loosing alpha) - the luminosity of the original image is preserved
    CGContextSetBlendMode(context, .Color)
    tintColor.setFill()
    CGContextFillRect(context, rect)

    // mask by alpha values of original image
    CGContextSetBlendMode(context, .DestinationIn)
    CGContextDrawImage(context, rect, self.CGImage)
    }
    }

    // fills the alpha channel of the source image with the given color
    // any color information except to the alpha channel will be ignored
    func fillAlpha(fillColor: UIColor) -> UIImage {

    return modifiedImage { context, rect in
    // draw tint color
    CGContextSetBlendMode(context, .Normal)
    fillColor.setFill()
    CGContextFillRect(context, rect)

    // mask by alpha values of original image
    CGContextSetBlendMode(context, .DestinationIn)
    CGContextDrawImage(context, rect, self.CGImage)
    }
    }

    private func modifiedImage(@noescape draw: (CGContext, CGRect) -> ()) -> UIImage {

    // using scale correctly preserves retina images
    UIGraphicsBeginImageContextWithOptions(size, false, scale)
    let context: CGContext! = UIGraphicsGetCurrentContext()
    assert(context != nil)

    // correctly rotate image
    CGContextTranslateCTM(context, 0, size.height);
    CGContextScaleCTM(context, 1.0, -1.0);

    let rect = CGRectMake(0.0, 0.0, size.width, size.height)

    draw(context, rect)

    let image = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()
    return image
    }

    }