How to Set the Opacity/Alpha of a Uiimage

How to set the opacity/alpha of a UIImage?

I just needed to do this, but thought Steven's solution would be slow. This should hopefully use graphics HW. Create a category on UIImage:

- (UIImage *)imageByApplyingAlpha:(CGFloat) alpha {
    UIGraphicsBeginImageContextWithOptions(self.size, NO, 0.0f);

    CGContextRef ctx = UIGraphicsGetCurrentContext();
    CGRect area = CGRectMake(0, 0, self.size.width, self.size.height);

    CGContextScaleCTM(ctx, 1, -1);
    CGContextTranslateCTM(ctx, 0, -area.size.height);

    CGContextSetBlendMode(ctx, kCGBlendModeMultiply);

    CGContextSetAlpha(ctx, alpha);

    CGContextDrawImage(ctx, area, self.CGImage);

    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();

    return newImage;
}

How to set the alpha of an UIImage in SWIFT programmatically?

Luckily I was able to help myself and would like to share with you my solution:

Swift 3

// UIImage+Alpha.swift

extension UIImage {  

    func alpha(_ value:CGFloat) -> UIImage {
        UIGraphicsBeginImageContextWithOptions(size, false, scale)
        draw(at: CGPoint.zero, blendMode: .normal, alpha: value)
        let newImage = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return newImage!   
    }
}

The above new Swift extension I added to my project and then I changed the UIButton example as follows, to have an alpha transparent background image with a transparency of 50%.

let img = UIImage(named: "imageWithoutAlpha")!.alpha(0.5)
let myButton = UIButton()

myButton.setBackgroundImage(img, for: .normal)

Set alpha for UIView/Image

Assuming titlePicture is a UIImageView, you can edit the alpha of it directly:

cell.titlePicture.alpha = (menuItems[indexPath.row] == currentItem) ? 0.6 : 1.0

Tweak the alpha values to your liking. Example output:

alpha = 1.0:

alpha = 0.6:

How can I set the Alpha of a UIImage?

You can't change the alpha of a UIImage. You could draw it with alpha to a new context and get a new image from that. Or you could extract the CGImage, then extract the data, then adjust the alpha bytes, then create a new CGImage from the data and a new UIImage from the CGImage.

But in this case, just use drawInRect:blendMode:alpha: instead of drawInRect:.

Change alpha of imageview of UIButton

To conclude the comments on both other answers: subclassing and/or adding another UIImageView is the simplest choice to archieve persistent, reliant behaviour.

How to make one color transparent on a UIImage?

-(void)changeColor
{
    UIImage *temp23=[UIImage imageNamed:@"leaf.png"];
    CGImageRef ref1=[self createMask:temp23];
    const float colorMasking[6] = {1.0, 2.0, 1.0, 1.0, 1.0, 1.0};
    CGImageRef New=CGImageCreateWithMaskingColors(ref1, colorMasking);
    UIImage *resultedimage=[UIImage imageWithCGImage:New];
}

-(CGImageRef)createMask:(UIImage*)temp
{
    CGImageRef ref=temp.CGImage;
    int mWidth=CGImageGetWidth(ref);
    int mHeight=CGImageGetHeight(ref);
    int count=mWidth*mHeight*4;
    void *bufferdata=malloc(count);

    CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB();
    CGBitmapInfo bitmapInfo = kCGBitmapByteOrderDefault;
    CGColorRenderingIntent renderingIntent = kCGRenderingIntentDefault;

    CGContextRef cgctx = CGBitmapContextCreate (bufferdata,mWidth,mHeight, 8,mWidth*4, colorSpaceRef, kCGImageAlphaPremultipliedFirst); 

    CGRect rect = {0,0,mWidth,mHeight};
    CGContextDrawImage(cgctx, rect, ref); 
    bufferdata = CGBitmapContextGetData (cgctx);

    CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, bufferdata, mWidth*mHeight*4, NULL);
    CGImageRef savedimageref = CGImageCreate(mWidth,mHeight, 8, 32, mWidth*4, colorSpaceRef, bitmapInfo,provider , NULL, NO, renderingIntent);
    CFRelease(colorSpaceRef);
    return savedimageref;
}   

The above code is tested and I changed the green color to red color by using mask

How to add alpha property to an UIImage set with SDWebImage?

Thanks to @Happiehappie 's comment and also this answer from another post I was able to apply the alpha property. Here is the final working code...

posterBackground.sd_setImage(with: URL(string: movieImage!), placeholderImage: UIImage(named: "poster-placeholder"), options: SDWebImageOptions(rawValue: 0), completed: { (image, error, cacheType, imageURL) in   
    self.posterBackground.image = image?.alpha(0.15)
})

How to remove opacity but keep the alpha channel of UIImage?

The following should do what you're after. Majority of the code is from How to set the opacity/alpha of a UIImage? I only added a test for the alpha value, before converting the colour of the pixel to black.

// Create a pixel buffer in an easy to use format
CGImageRef imageRef = [[UIImage imageNamed:@"testImage"] CGImage];
NSUInteger width = CGImageGetWidth(imageRef);
NSUInteger height = CGImageGetHeight(imageRef);
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

UInt8 * m_PixelBuf = malloc(sizeof(UInt8) * height * width * 4);

NSUInteger bytesPerPixel = 4;
NSUInteger bytesPerRow = bytesPerPixel * width;
NSUInteger bitsPerComponent = 8;
CGContextRef context = CGBitmapContextCreate(m_PixelBuf, width, height,
                                             bitsPerComponent, bytesPerRow, colorSpace,
                                             kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);

CGContextDrawImage(context, CGRectMake(0, 0, width, height), imageRef);
CGContextRelease(context);

//alter the alpha when the alpha of the source != 0
int length = height * width * 4;
for (int i=0; i  if (m_PixelBuf[i+3] != 0) {
    m_PixelBuf[i+3] = 255;
  }
}

//create a new image
CGContextRef ctx = CGBitmapContextCreate(m_PixelBuf, width, height,
                                         bitsPerComponent, bytesPerRow, colorSpace,
                                         kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);

CGImageRef newImgRef = CGBitmapContextCreateImage(ctx);
CGColorSpaceRelease(colorSpace);
CGContextRelease(ctx);
free(m_PixelBuf);

UIImage *finalImage = [UIImage imageWithCGImage:newImgRef];
CGImageRelease(newImgRef);

finalImage will now contain an image where all pixels that don't have an alpha of 0.0 have alpha of 1.

how to set alpha on Backgroung image using Swift

if you want to set alpha on only background image, then re-create UIImage with changing the alpha value.

if you want to set alpha to entire button, then simply set alpha value to the button.

centerButton.alpha = 0.5

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