A question came up in the comments to my previous post:

Any suggestions on the best way to edit DDS files on a Mac?

The answer is simple: do not edit DDS files!!!

The problem is simple: DDS is a lossy compressed format.  Every time you go from an uncompressed/losslessly compressed format (like PNG, TIFF, or BMP) to a lossy format (like DDS or JPEG) you are going to lose a little bit of image quality.  So if you re-open your DDS, edit it, and resave, your graphics program is going to make a round trip and reduce quality.

Therefore the work flow should be:

  1. Edit the original PNG or photoshop master file.
  2. When done, re-export to DDS.

So each time you work, you work from a lossless or uncompressed master (like PNG or a gimp/photoshop file) and then re-export to DDS.

About Ben Supnik

Ben is a software engineer who works on X-Plane; he spends most of his days drinking coffee and swearing at the computer -- sometimes at the same time.

7 comments on “Do Not use DDS as an Editing Format!”

  2. Oops! actually, what I meant was import PNG/export DDS.

    I have some re-paints for V9 aircraft that suffer from lo-res. I was hoping to take the PNG files, tidy them up and export/save them as DDS but Photoshop CS5 won’t accept any of the NVidia plug-ins.

    Having read some more since the previous post, I’m assuming that DDS.XGrinder is the way to go?

    Sorry to give you palpitations – as I graphic designer I’m well up on the wrongness of back and forths on lossy formats 😉

  3. And one final point should be that it seems worthwhile to split objects and textures into separate files according to whether they require an alpha channel, allowing the texture without alpha to compress under DXT1 for less VRAM overhead.

    Seems a worthwhile endeavor even for one’s scenery file collection, if you have the disk storage space.

    1. If you are authoring a scenery pack, then yes.
      For an existing scenery pack, I don’t think you can retro-fit this kind of texture space allocation onto an existing pack easily.

  4. “The problem is simple: DDS is a lossy compressed format.”

    DDS has many different internal formats. Only a some of them are lossy, the rest are lossless. It’s the DXT1-DXT5 modes that are compressed lossy formats (plus some less common ones like BC4U, BC4S, ATI2 and BC5S).
    Using DDS as an editing format is fine, as long as you use one of the many lossless raw formats it supports.
    For example, Paint.Net has 11 pixel formats for DDS files, only 3 of those are lossy.

    1. Absolutely correct – a more nuanced and correct rule would have been “don’t use DDS as an editing format with DXTn as your internal image format.” But since X-Plane only uses DDS files for DXT I simplified!!

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