Cocoa-Touch: How to set the interpolation quality to be used by a UIImageView?

Question

I have a UIImageView showing a image that is larger than it's frame.
It's set to rescale the image to fit it's frame. But, the image is scaled with a low quality filter.

I've read here that this is caused by it using a low interpolation quality.

How can I get it's context to CGContextSetInterpolationQuality to kCGInterpolationHigh?

score 2 · Answer 1 · edited May 23 '17 at 12:07

2

From "UIImageView scaling/interpolation", this is the most streamlined way to do it if you can:

[[yourimageview layer] setMagnificationFilter:kCAFilterTrilinear]

Be sure to #import <QuartzCore/CALayer.h>

A warning on kCAFilterTrilinear: "Some renderers may ignore this, or impose additional restrictions, such as source images requiring power-of-two dimensions."

edited May 23 '17 at 12:07

Community

1
1

answered Jul 29 '14 at 01:58

Kaolin Fire

2,521
28
43

score 1 · Answer 2 · answered Nov 01 '09 at 17:45

1

CGContextSetInterpolationQuality is a function. You need to call it with whatever parameters are appropriate for your situation.

http://developer.apple.com/mac/library/qa/qa2001/qa1186.html

answered Nov 01 '09 at 17:45

Azeem.Butt

5,855
1
26
22

And where do you call this function to apply it to the UIImageView's drawing? – Peter Hosey Nov 01 '09 at 19:55
1

I'd draw the image into a new context using this setting, take the resulting UIImage, and set the UIImageView.image property to the refined image. – Kendall Helmstetter Gelner Nov 01 '09 at 20:19

Ole Begemann · Accepted Answer · 2009-11-01T18:50:38.650

1

UIImageView does not offer this functionality, though UIImage has an undocumented _imageScaledToSize:interpolationQuality: method if I remember correctly.

Since UIImageView draws directly to the display, subclassing and overriding drawRect: is no option (thanks to Prody for pointing this out). The only option I see is to create a custom UIView subclass with a custom drawrect: implementation.

edited Nov 01 '09 at 18:50

answered Nov 01 '09 at 17:57

Ole Begemann

135,006
31
278
256

From the docs: The UIImageView class is optimized to draw its images to the display. UIImageView will not call drawRect:. I can't find any mention of _imageScaledToSize:interpolationQuality. I guess for now I'll draw my image in the parent view's drawRect. – Prody Nov 01 '09 at 18:21
Thanks for the correction, Prody. I should have read the docs before posting. I will edit my answer accordingly. – Ole Begemann Nov 01 '09 at 18:47

Cocoa-Touch: How to set the interpolation quality to be used by a UIImageView?

3 Answers3