Images are an integral part of every application.  Resizing images have been a recurrent problem for all developers.  With camera resolution increasing and devices getting fragmented, it is crucial that the algorithm used to resizing provide accurate results. 

In this article I’ll be empirically going over image resizing techniques and best possible solution to resizing images focusing on quality of image. 

Techniques to resize

Here I am going to go over four methods to resize images.  All focused on generating the best quality of image. 

I am going to compare all resized images with a reference image.  Lets generate the reference image from Photoshop(Bicubic).  We’ll compare the images graphically and then emperically with Average Error. 

UIKit

UIKit resizing is the simplest of resizing and produces good results. 

CoreGraphics

Using CoreGraphics quality of the image is identical to the UIKit image.  Atleast I could not perceive any difference and imagediff also gave no difference.  Only difference is in the performance. 

Let’s see the difference between the core graphics image and the original.  If you look closely at the gif, you can notice that the image is blurry.  We might need to sharpen this image a little or use another method to resize to generate better results. 

CoreImage

CoreImage produces quite interesting results.  This being the slowest of all the methods, I assumed to produce much better quality images but seems to be generating lot of resizing artifacts. 

Here is a comparison of CoreImage resizing result with original image. 

You can notice that the lights appear more brighter than it should be.  This artifact occurs in all images resized with CoreImage.  Image also seems slightly more sharper generally. 

vImage

This poorly documented little framework packs a very strong punch.  The results are astonishing.  This produces the best results with perfectly crisp and balanced image.  Less blurring compared to CG.  Sharper than CG.  Not as unnaturally sharp as CI.