Problem with image property dictionaries

Question

Can anyone talk me through the concepts of image Property Dictionaries? I want to save a TIFF file that has a TIFF Dictionary with some keys.

I'm working in python, but any advice would be welcome.

My current code is:

options = { 
     kCGImagePropertyTIFFDictionary: 'TIFFDictionary', 
     kCGImagePropertyTIFFXResolution: "300", 
     kCGImagePropertyTIFFYResolution: "300", 
     kCGImagePropertyTIFFResolutionUnit: 2 } 
CGImageDestinationAddImage(destination, image, options)

But they don't get saved to the TIFF file. I don't understand where and how I need to use

kCGImagePropertyTIFFDictionary.

https://developer.apple.com/documentation/imageio/cgimageproperties/format_specific_dictionaries

From the documentation it looks like the keys need to be inside kCGImagePropertyTIFFDictionary somehow.

AppKit

815

Posted by

benwiggy

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Answer 1

In fact, I don't even need a TIFF Dictionary. I can just use:

  resolution = 300
  options = {
       kCGImagePropertyDPIHeight: resolution
       kCGImagePropertyDPIWidth: resolution
  }

, which will work for other formats, too.

Software is never finished!

Posted by

benwiggy

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Answer 2

You may have a look at this other thread to see how the dictionary is referenced.

h ttps://forums.developer.apple.com/thread/86498

Posted by

Claude31

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Answer 3

Thanks. That seems to suggest that I need a dictionary with kCGImagePropertyTIFFDictionary as a key and another dictionary as the value; the second dict contains all the other key-value pairs.

(Not sure why kCGImagePropertyDepth is at the same meta-level as the TIFF Dictionary..... but still.)

I tried that in python but it completely stopped the images being created altogether. I'll keep experimenting.

Posted by

benwiggy

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Answer 4

Fixed it! It turns out that the numbers need to be, unsurprisingly, numbers, not strings, which I'd inferred from Apple's documentation.

And the Dictionary constant is indeed a key whose value is another dictionary.

options = {
Quartz.kCGImagePropertyTIFFDictionary: {
Quartz.kCGImagePropertyTIFFXResolution: 300,
Quartz.kCGImagePropertyTIFFYResolution: 300,
Quartz.kCGImagePropertyTIFFResolutionUnit: 2
}}

Posted by

benwiggy

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Answer 5

Happy you solved the issue and thanks for having given this feedback.

Don't forget to close the thread as solved.

Posted by

Claude31

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Answer 6

In fact, I don't even need a TIFF Dictionary. I can just use:

  resolution = 300
  options = {
       kCGImagePropertyDPIHeight: resolution
       kCGImagePropertyDPIWidth: resolution
  }

, which will work for other formats, too.

Software is never finished!

Posted by

benwiggy

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Problem with image property dictionaries

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