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I am reading a tiff into an NSImage. I am creating another NSImage. I am trying to composite the first NSImage into the second.

The problem I’m having is that the NSImage that I create is always set up at 72 DPI and the NSImage that I read in is at various DPIs and when I composite the one into the other it changes it’s size.

Is there a way to determine the DPI of an NSImage so that I can create the new NSImage at the same DPI?

You can get the actual size of the NSImage, and get the pixel size of the NSBitmapImageRep which contains the actual TIFF data, and then a simple division gets you the DPI.

Here’s what I use to show the images at system dpi - which is 72 on Tiger AFAIU - BjoernKriews

    [image setScalesWhenResized: YES];
    NSBitmapImageRep *rep = [image bestRepresentationForDevice: nil];
    NSSize pixelSize = NSMakeSize([rep pixelsWide],[rep pixelsHigh]);
    [image setSize: pixelSize];

Thanks, but that code didn’t seem to help. Still, when I composite the 200 DPI image (that I’m reading in) into the 72 DPI image (that I’m creating), the compositied image is coming in much smaller. —-

You may be better served by skipping NSImage altogether and going directly to NSBitmapImageRep.

I don’t see how that will solve my issue - will it? I mean, I still need to composite one image into another of different size. And how can I just use NSBitmapImageRep without going through an NSImage?


check out the example code posted here -> ImageCompositing

Thanks everyone - I see now. NSBitmapImageRep’s -size isn’t the same as it’s -pixelWidth and -pixelHeight. Setting the my NSImage’s size to NSBitmapImageRep’s size does the trick. —- Thank you! I wrote my own screen-saver to display iPhoto albums (with more options than the built-in photo savers), and I’ve been beating my head against my keyboard trying to figure out how to force 72 dpi on the JPG files. I’ve got a bunch of slides scanned at very high resolutions that look like postage stamps on my screen. When I force stretching it get very pixelated images. This solves my problem nicely. —-