Support CMYK conversion (for TIFFs)

[sophie-h]

The following image

• https://exoplanets.nasa.gov/rails/active_storage/blobs/eyJfcmFpbHMiOnsibWVzc2FnZSI6IkJBaHBBaXdGIiwiZXhwIjpudWxsLCJwdXIiOiJibG9iX2lkIn19--bb2d9b418904bbf57e31960b5174b487a5da70de/Dark_Matter_27x39_ENGLISH_copy_UPDATED.tif

gives this error with image-rs

The decoder for Tiff does not support the color type `Unknown(32)`

I'm not sure if that's the exact same missing feature as image-rs/image-tiff#202 since instead of "palette", this image reports "separated."

=== TIFF directory 0 ===
TIFF Directory at offset 0x8 (8)
  Subfile Type: (0 = 0x0)
  Image Width: 8100 Image Length: 12021
  Resolution: 300, 300 pixels/inch
  Bits/Sample: 8
  Compression Scheme: LZW
  Photometric Interpretation: separated
  Orientation: row 0 top, col 0 lhs
  Samples/Pixel: 4
  Rows/Strip: 8
  Planar Configuration: single image plane
  Software: Adobe Photoshop 22.0 (Windows)

[sophie-h]

This section describes how to store separated (usually CMYK) image data in a
TIFF file.

Looks like we are dealing with "Section 16: CMYK Images" of TIFF 6.0

[fintelia]

I think this error is actually coming from the main image crate which doesn't support all the color formats that image-tiff does. Specifically if I'm interpreting the output correctly, the tiff file is in CMYK format and while this crate is perfectly happy to extract the contents, we currently lack the ability to convert to RGB which would be needed to produce a DynamicImage.

You can see TiffDecoder:new for where the supported vs. unsupported determination is made

[sophie-h]

Yeah, image-tiff is working as expected here. Can you move this to image-rs?

Converting CMYK to RGB sounds easy enough. (Famous last words.)