Grayscale texture filesize questions

So I am doing some “Researching” to see if I can optimise some stuff.
I got a few grayscale textures but lets narrow it down to one for now.
Its a 4096/4096 roughness texture, its grayscale and saved as an uncompressed .PNG.

The file is 29,4 MB.

After importing it, its set to TC_Default + SRGB. (DXT1)
Filesize: 72.2 MB. almost 250% bigger than the original filesize?

So I changed it to not use TC_GrayScale + RGB (G8)
Filesize: 72.2 MB.

This is both with and without mipmaps.


  1. what is the advantage of using grayscale?
  2. Why is the filesize so darn big?
  3. did I do anything wrong to get these weird filesizes?


Hey Luos -

From one of our talented Rendering Engineers:

"The file size of the .uasset file is not necessarily representative of the in-game memory usage of a texture. In theory, a DXT1 texture uses 0.5 bytes per pixel and a G8 uses 1 byte per pixel, so it should only be double memory usage. However, it’s possible that a G8 texture is actually stored as R8G8B8 in the .uasset file, or something like that. It may not be the same when your game has been cooked and loaded in-game.

In any case, you should use the console command “ListTextures” instead, while running your game stand-alone (not via the Editor). This will dump real information about all your textures in-game to the log. You can copy/paste those lines from the log into Excel (and “convert text to multi-column”) to look through all your textures. Find your G8 texture. It should be 1 byte per pixel, adding all mips together. If I remember correctly, the total size should be about 1.43 multiplied by the size (in bytes) of your first mip-level"

Thank You

Eric Ketchum