I want to grab a subimage from a UIImage. I've looked around for a similar question, to no avail.
I know the range of pixels I want to grab - how can I return this subimage, from an existing image?
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3 Answers
This should help: http://iphonedevelopment.blogspot.com/2010/11/drawing-part-of-uiimage.html
This code snippet is creating a category of UIImage but the code should be easily modified to work without it being a category.
A shorter way of doing the same thing is the following:
CGRect fromRect = CGRectMake(0, 0, 320, 480); // or whatever rectangle CGImageRef drawImage = CGImageCreateWithImageInRect(image.CGImage, fromRect); UIImage *newImage = [UIImage imageWithCGImage:drawImage]; CGImageRelease(drawImage); Hope this helps!
3 Comments
AechoLiu
This way should run under main thread, it is not a thread-safe method.
ohcibi
This won't work for retina devices, as it'll cut the raw image and not the representation in the retina screen (i.e. if 320x480 is the normal and 640x960 the retina resolution of the original image, the CGRect with (0, 0, 320, 480) would cut out the upper left quarter of the image when on retina)
Mecki
@ohcibi To make this coed also work with retina, you need to get the scale factor of the image (
image.scale), apply it to the rect (multiply all numeric values by that factor) and when creating the final UIImage, use the method imageWithCGImage:scale:orientation: to set the correct scale factor again.Updated @donkim answer for swift 3:
let fromRect=CGRect(x:0,y:0,width:320,height:480) let drawImage = image.cgImage!.cropping(to: fromRect) let bimage = UIImage(cgImage: drawImage!) 
Comments
In Swift 4, taking into account screen scale (otherwise your new image will be too large):
let img = UIImage(named: "existingImage")! let scale = UIScreen.main.scale let dy: CGFloat = 6 * scale // say you want 6pt from bottom let area = CGRect(x: 0, y: img.size.height * scale - dy, width: img.size.width * scale, height: dy) let crop = img.cgImage!.cropping(to: area)! let subImage = UIImage(cgImage: crop, scale: scale, orientation:.up) 