howard10 howard10 - 3 months ago 28
Objective-C Question

iOS UIImageView scaling image down produces aliased image on iPad 2

I am using UIImageView to display thumbnails of images that can then be selected to be viewed at full size. The UIImageView has its content mode set to aspect fit.

The images are usually scaled down from around 500px x 500px to 100px x 100px. On the retina iPad they display really well while on the iPad2 they are badly aliased until the size gets closer to the native image size.


Original Image

Original Image

Retina iPad 100x100

Retina iPad rendering at 100px x 100px

iPad 2 100x100

iPad 2 rendering at 100px x 100px

The difference between iPad 2 and new iPad might just be the screen resolution or could be that the GPU is better equipped to scale images. Either way, the iPad 2 rendering is very poor.

I have tried first reducing the image size by creating a new context, setting the interpolation quality to high and drawing the image into the context. In this case, the image looks fine on both iPads.

Before I continue down the image copy/resize avenue, I wanted to check there wasn't something simpler I was missing. I appreciate that UIImage isn't there to be scaled but I was under the impression UIImageView was there to handle scaling but at the moment it doesn't seem to be doing a good job scaling down. What (if anything) am I missing?

Update: Note: The drop shadow on the rendered / resized images is added in code. Disabling this made no difference to the quality of the scaling.


Another approach I've tried that does seem to be improving things is to set the minificationFilter:

[imageView.layer setMinificationFilter:kCAFilterTrilinear]

The quality is certainly improved and I haven't noticed a performance hit.