Retina version of an image always used on non-retina display

Question

In Cocoa application I've got 16x16 and 32x32 @2x version of an image: . When the image is displayed in NSImageView Mac OS X always picks higher-resolution version (i.e. downscales the @2x image on non-retina displays instead of using the 1:1 version).

(IB on the left = good, running app on the right = downscaled mess)

Of course I've got both images added to the project (as image.png and [email protected]).

If I delete the @2x image from app bundle then OS X will display the lower-resolution image.

The bug happens regardless whether Xcode (4.6.2) combines them into a .tiff or not (and I've checked that the combined .tiff contains both images).

Oddly this happens only with this particular image. Other 1x/2x images in the same project are displayed correctly matching screen DPI.

How is that possible?! Do images have to meet some special criteria other than size and filename pattern?

Answer 1

Mystery solved: OS X doesn't like mixed types of PNGs.

$ file *.png
image.png: PNG image data, 16 x 16, 8-bit gray+alpha, non-interlaced
[email protected]: PNG image data, 32 x 32, 8-bit colormap, non-interlaced

if both files are forced to use same color mode (i.e. both gray or both paletted) then OS X selects images correctly.