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Creeju
Participating Frequently
October 18, 2022
Question

Photoshop loses pixel data for 16-bit (48-bit) TIF files when saving

  • October 18, 2022
  • 2 replies
  • 3159 views

I was comparing 24-bit and 48-bit depth for archival scanning, when I came across this bug.

Technical info/version:

Adobe Photoshop Version: 23.5.1 20220907.r.724 5600b96  x64
Betriebssystem: Windows 10 64-Bit
Version: 10 10.0.19044.2130
ImageMagick-7.1.0-Q16-HDRI

How to reproduce:

  1. Open 48-bit TIF in Photoshop
  2. Save TIF (compressed or uncompressed doesn't matter, as long as it is lossless)
  3. Compare pixel data with ImageMagick compare (options -compose Src -highlight-color White -lowlight-color Black to get black/white diff only)
  4. Observe vastly different pixel data for 48-bit files

Repeating the same procedure for my 24-bit scans results in black comparison frame, showing zero difference.

 

I can not insert the source files into this post, because the scans are bigger than 47 MB. If external links are fine, I can upload them somewhere else.

This topic has been closed for replies.

2 replies

davescm
Community Expert
davescmCommunity Expert
Community Expert
April 20, 2023

As explained above Photoshop does not use the full 16 bit data, but for photographic purposes the difference is academic and the delta to each pixel is so small it cannot be seen by eye. It was explained some time ago that using 15 bit +1 was built into the core processing for speed and to give a middle value which works better for certain image processing. For viewing images it does not result in a visible difference.

 

There are some specific use cases where it does matter, for example 3D height maps or specific scientific purposes. For those, either using other software or converting elsewhere to 32 bit float and opening in Photoshop are appropriate.

 

Dave

    C
    CreejuAuthor
    Participating Frequently
    April 20, 2023

    Would it be possible to notify the user of this change when saving or opening an image, before the data is lost? I support the notion that this is not for visual fidelity, but I had no way of knowing this without getting the information on the forum. It is unexpected behavior.

    Is the performance boost of the 15 bit +1 still needed today? I do not know if Adobe would be touching the core, but carying this along might not be necessary anymore and providing regular 16 bit-processing would give a more consistent user experience with standardized formats.

      davescm
      Community Expert
      davescmCommunity Expert
      Community Expert
      April 20, 2023

      I don't work for, therefore cannot speak for Adobe.

      I have no idea how much work would be involved in rewriting such a core function of what is now a huge application, along with any other associated functionality that uses and depends on that 15 bit+1 processing. I suspect a lot more than we would think given that Photoshop has used this method since 16 bit/channel support was introduced in 1993 (version 2.5 ).

       

      Dave

        J
        J453
        Legend
        October 18, 2022

        External links work fine for sharing files.  Post a URL to the file using CC files or dropbox, or something similar to share the file.

          C
          CreejuAuthor
          Participating Frequently
          April 20, 2023

          I did some more testing and came up with an easier way to reproduce the issue, with smaller files as well.

          1. Create 48-bit (16-bit) image in Gimp.
          2. Export image to png and/or tif
          3. Open png/tif in Photoshop and save to a second png/tif file
          4. Use magick.exe compare -compose Src -highlight-color White -lowlight-color Black INPUT1 INPUT2 PNG32:OUTPUT.png to compare the files.
          5. Observe vast difference in pixel data.

           

          Test files and comparisons are attached. As I initially pointed out, this issue also occurs for output files of scanning software and is not expected behavior.

          I cannot attach tif-files, so I included the png.

          C
          CreejuAuthor
          Participating Frequently
          April 20, 2023

          To illustrate the issue, this is the base image made in Gimp:

           Executing the comparison to the Photoshop-save should give a black frame for identical pixel data. These are the acutal results for png and tif:

            

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