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MSFS20 Question about 16/8 bit and DDS file type and it's size

S

Senchay

Messages
246
Country
germany
Hello.

I've tried to search but seems the search funktion doesn't let me search for dds file size, it tells me it would be too short (only looks for dds).

Yesterday I came around some, for me, weird behavior with the size of a dds file after the png got converted to dds.

Before I had a chat with some member from here about 16 bit and 8 bit and how the use of a 8 bit albedo can save a lot of file size without visual loss of quality. I wanted to give it a go.

Then I went to my substance painter textures and re-exported them in 8 bit.
Yes, the png that came out then was indeed 1/3 of the size of a 16 bit export.

I applied this one 8 bit albedo to my blender object and exported the gltf.
I thought "amazing, that saves me lots of space". Until I built the project. Because now it has the identical file size like the one with the 16 bit had.

At one point I took a look at my texture output folder. And to my surprise, nearly every single dds texture had the exact same size. Despite having very different pngs as source, ranging from 20 to 70 mb per image.

Can be seen here, they all have 21,8 mb

unknown.png


Further down I saw some of the textures that have only the half of it, 10,9 mb (not visible in pic). All of them were 4k 16bit. I wondered why on earth some have 21.8 and others 10.9 with the same export settings and had a look at the UV map.

Nothing special, it was filled like the bigger ones. couldn't see any difference that leads to the double file size.

I discussed this with 3 other ppl now and they confirm this is the case after they build the project too. Amd none of them had an explanation, basically all of em were rather surprised of this.

So my questions are 2 basically:

1 what defines the file-size of a DDS file after it got converted from a PNG.

2 what meaning has 8 and 16 bit png, if after being converted they have the exact same file-size?

Would be great to get some insight here.
 
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The msfs converter might be converting them to 16 bit rather than 8 bit. That would be the logical thing that is happening.
 
It looks like that on first sight, yes.

Hmm, is there maybe a way to influence this? Because at some point in the SDK there is something like "At least the roughness and AO and Metal map should be 16 bit. Sounds for me as if one can do other things than 16 bit too. That was somewere at the Landscape Elements Section, or Texture Quality. Ill look out for it.

Also still wonder why some seemingly have the exact half file-size, despite them being 4k either.

So if its really like that and the converter always does 16 bit i guess the extra save of the png in 8 bit is useless and probably better to have it 16 and let the converter do the rest.

"It is recommended to use a lossless format at 16 bits per pixel, such as the 16 bpp *.PNG format. This is especially important for roughness, metal and/or occlusion maps, where Microsoft Flight Simulator remaps the data to a curve to have more precision in the dark areas before compressing (which is then remapped again later in the shader)."
 
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Ok, i found that those with 10.9 MB are the Albedos. All normals and metal maps have 21.8 and all albedos have 10.9 (also the ones where i didnt convert to 8 bit). This looks like the converter does the thing already by himself? I mean he creates all metal and normals in 32 bit and all albedos in 8 bit?

Interesting to see that all DDS have same sizes, this is probably because of the memory "friendly" format that it calls himself? Maybe this is easier for vram/ram to handle or something? No idea.... just thinking out loud, never saw something like this.

But what it also means is that it fits what i often experience, there is some point where the 4k details doesnt make much difference anymore, so its shrinking information (in case of the 16 bit png input with more than 21.8 mb) and raises noise (in case of png inputs that re below 10.9 mb). Interesting.
 
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