how to change rgb value of an image in iOS? - ios

Question

I have a UIImage and I want to decrease the rgb value of each point , how can I do that?
or how can I change one color to another color in an image?
[Xcode8 , swift3]

Answer 1

This answer only applies if you want to change individual pixels..
First use UIImage.cgImage to get a CGImage. Next, create a bitmap context using CGBitmapContextCreate with the CGColorSpaceCreateDeviceRGB colour space and whatever blend modes you want.
Then call CGContextDrawImage to draw the image to the context which is backed by a pixel array provided by you. Cleanup, and you now have an array of pixels.
- (uint8_t*)getPixels:(UIImage *)image {
CGColorSpaceRef cs= CGColorSpaceCreateDeviceRGB();
uint8_t *pixels= malloc(image.size.width * image.size.height * 4);
CGContextRef ctx= CGBitmapContextCreate(rawData, image.size.width, image.size.height, 8, image.size.width * 4, cs, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
CGColorSpaceRelease(cs);
CGContextDrawImage(ctx, CGRectMake(0, 0, image.size.width, image.size.height));
CGContextRelease(ctx);
return pixels;
}
Modify the pixels however you want.. Then recreate the image from the pixels..
- (UIImage *)imageFromPixels:(uint8_t *)pixels width:(NSUInteger)width height:(NSUInteger)height {
CGDataProviderRef provider = CGDataProviderCreateWithData(nil, pixels, width * height * 4, nil);
CGColorSpaceRef cs = CGColorSpaceCreateDeviceRGB();
CGImageRef cgImageRef = CGImageCreate(width, height, 8, 32, width * 4, cs, kCGBitmapByteOrderDefault | kCGImageAlphaPremultipliedLast, provider, nil, NO, kCGRenderingIntentDefault);
pixels = malloc(width * height * 4);
CGContextRef ctx = CGBitmapContextCreate(pixels, width, height, 8, width * 4, cs, kCGBitmapByteOrderDefault | kCGImageAlphaPremultipliedLast);
CGContextDrawImage(ctx, (CGRect) { .origin.x = 0, .origin.y = 0, .size.width = width, .size.height = height }, cgImage);
CGImageRef cgImage = CGBitmapContextCreateImage(ctx);
UIImage *image = [UIImage imageWithCGImage:cgImage];
CGImageRelease(cgImage);
CGContextRelease(ctx);
CGColorSpaceRelease(cs);
CGImageRelease(cgImageRef);
CGDataProviderRelease(provider);
free(pixels);
return image;
}

Answer 2

One of the ways is to use image as a template and to set color which you want.
extension UIImageView {
func changeImageColor( color:UIColor) -> UIImage
{
image = image!.withRenderingMode(.alwaysTemplate)
tintColor = color
return image!
}
}
//Change color of logo
logoImage.image = logoImage.changeImageColor(color: .red)