ImageQuality with CGContextSetInterpolationQuality

Question

How effective is the CGContextSetInterpolationQuality method in Quartz?

Does it affect the quality of the image? If so, to what extent?

I can't see any difference between the interpolated and the non-interpolated image.

Answer 1

Although this is a bit of an old question, I have recently done some benchmarking about the effects of CGContextSetInterpolationQuality and thought that its outcomes might be of interest to someone else.

In my benchmark test, I draw a set of 6 different 649x649 b&w bitmap images to build a set of 12 different jigsaw puzzle tiles. The bitmap images are scaled down by a factor of 5.0 (i.e., to 129.8x129.8) to make them fit on a 320x480 display (at retina display scale).

Run times on a 4th gen iPod touch, as reported by Instruments, are the following:

• kCGInterpolationLow: 969 msec

• kCGInterpolationMedium: 1690 msec

• kCGInterpolationHigh: 2694 msec

• kCGInterpolationNone: 545 msec

As to the visual outcome, if you compare High or Medium to Low or None, the difference is staggering. Even noticeable, IMO, the difference between None and Low; while the difference between High and Medium is not particularly noticeable in this particular test. What is clear is the difference in run times, so that in my particular case, I ended up using kCGInterpolationMedium.

kCGInterpolationNone

kCGInterpolationLow

kCGInterpolationMedium

kCGInterpolationHigh