Question

I searched everywhere but didn’t find the solution. I have image 1. How can I programatically tint them with gradient to get images 2 and 3? Here are those images:

Tints that I applied to them via Photoshop are simple 2-color linear gradients.

And my question is: how can I achieve this effect programatically?

---

Solution: jrtc27 gave me almost working example. I fixed it (for ARC) and made it reusable (using UIImage’s category). Here is it:

- (UIImage *)tintedWithLinearGradientColors:(NSArray *)colorsArr {
    CGFloat scale = self.scale;
    UIGraphicsBeginImageContext(CGSizeMake(self.size.width * scale, self.size.height * scale));
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextTranslateCTM(context, 0, self.size.height);
    CGContextScaleCTM(context, 1.0, -1.0);

    CGContextSetBlendMode(context, kCGBlendModeNormal);
    CGRect rect = CGRectMake(0, 0, self.size.width * scale, self.size.height * scale);
    CGContextDrawImage(context, rect, self.CGImage);

    // Create gradient

    UIColor *colorOne = [colorsArr objectAtIndex:1]; // top color
    UIColor *colorTwo = [colorsArr objectAtIndex:0]; // bottom color


    NSArray *colors = [NSArray arrayWithObjects:(id)colorOne.CGColor, (id)colorTwo.CGColor, nil];
    CGColorSpaceRef space = CGColorSpaceCreateDeviceRGB();
    CGGradientRef gradient = CGGradientCreateWithColors(space, (__bridge CFArrayRef)colors, NULL);

    // Apply gradient

    CGContextClipToMask(context, rect, self.CGImage);
    CGContextDrawLinearGradient(context, gradient, CGPointMake(0,0), CGPointMake(0,self.size.height * scale), 0);
    UIImage *gradientImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return gradientImage;
}

Answer 1

EDIT: Here is a version which supports non-retina and retina displays

The method can be used as a category for UIImage

+ (UIImage *)imageWithGradient:(UIImage *)img startColor:(UIColor *)color1 endColor:(UIColor *)color2 {
    UIGraphicsBeginImageContextWithOptions(img.size, NO, img.scale);
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextTranslateCTM(context, 0, img.size.height);
    CGContextScaleCTM(context, 1.0, -1.0);

    CGContextSetBlendMode(context, kCGBlendModeNormal);
    CGRect rect = CGRectMake(0, 0, img.size.width, img.size.height);
    //CGContextDrawImage(context, rect, img.CGImage);

    // Create gradient
    NSArray *colors = [NSArray arrayWithObjects:(id)color2.CGColor, (id)color1.CGColor, nil];
    CGColorSpaceRef space = CGColorSpaceCreateDeviceRGB();
    CGGradientRef gradient = CGGradientCreateWithColors(space, (__bridge CFArrayRef)colors, NULL);

    // Apply gradient
    CGContextClipToMask(context, rect, img.CGImage);
    CGContextDrawLinearGradient(context, gradient, CGPointMake(0,0), CGPointMake(0, img.size.height), 0);
    UIImage *gradientImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    CGGradientRelease(gradient);
    CGColorSpaceRelease(space);

    return gradientImage;
}

Edit: added change by sobri