NSImageRep wrong resolution?

Question

MacOS 10.7.4 comes with new icons having image reps at 144 DPI. The bad thing is that when I load one of these icons in a NSImage I only get reps having a size of 512px. I mean: I load a 1024px/144dpi icns file in a NSImage and then I ask every image rep for its size... no rep has a size of 1024px, I only get sizes with a max. of 512px (no matter if a rep has a resolution of 72dpi rather than 144dpi: in fact new icons in 10.7.4, like TextEdit or Automator, have reps for both resolutions for each size except for 1024px which exists in a single rep at 144dpi).

Whay does NSImageRep seem like it doesn't understand its real resolution? Why do I get this issue just for 1024px/144dpi and not, for example, for 512px/144dpi?

If I read the TIFFRepresentation of the NSImage and I write it back to a file I get a correct 1024px/144dpi TIFF file, while if I write the same NSImage going through CGImageSource/CGImageDestination as kUTTypeTIFF I get a 1024px/72dpi file.

All these things are making me getting very confused.

Thanks a lot

Answer 1

The docs for -[NSImageRep size] say:

The size of the image representation, measured in points in the user coordinate space.

(Emphasis added.)

This is not a measurement in pixels. It's a measurement in points, so an image that is 1024 pixels at 144 dpi measures 512 points when the points are 72 dpi.

You want to query the -pixelsWide and -pixelsHigh methods (if, indeed, you care about the pixel dimensions; often you should not).