FS2004 Weird color in DTX1

[sfrenchie]

Hello all,

I create a texture for a building in Photoshop CS2, create a .bmp then open it with DXTBmp and look at the result. The whites are turning to yellowish. Anyone knows why, how to fix that, etc?



Thanks

 

[tgibson]

Hi,

Before conversion, change the whites so the RGB values are exactly the same (200,200,200 for example). Then the conversion shouldn't affect the color.

Hope this helps,

 

[sfrenchie]

Thanks for the tip. So you mean do a selection by color and even up the RGB on the selected "whites" hum?

 

[tgibson]

Hi,

Yep, that's the way.

 

[arno]

Hi,

I find it hard to see the yellows in the screenshot, but the DXT format uses compression to store the colours. For every area of 4x4 pixels it uses maximum 4 colours. And these colours have to be linear interpolated between two RGB values. So if you have a lot of different pixel colours in that 4x4 area the compression will result in slightly changed colours. This could explain the yellow colour.

 

[tgibson]

PS. The easiest way to do what I said is convert that white "area" to grayscale, which is all RGB values being equal.

I think the reason is works is that it significantly reduces the total number of colors in a given area.

Hope this helps,

 

[sfrenchie]

Arno, Tom, thanks to both of you for your input. It seems you both are saying the same in different ways or rather one gives me the explanation and the other gives me the "how to fix the issue".

This problem mostly occurs with roof images I get from Google map. Since it's full of pixels of different colors your explanation, Arno, makes perfect sense. I guess the issue will always occur with any type of picture containing light colors (as it is not so noticeable with dark colors.)

Since those texture are fairly simple (no transparency, etc.) and are used on buildings my question is: is there another format that could be used in a satisfactory manner? Is DXT the only format storing mipmaps?
I see in the 'texture' folder that even MS has a bunch of images that are just plain .bmp.

Thanks

 

[n4gix]

They may have a simple .bmp extension, but they are all compressed images! DXT3 is the compression used most often.

The only 24bit bitmaps used by FS is in the ..\panel folder where the 2d panel images are kept.

 

[tgibson]

Hi,

Sometimes conversion to 8 bit (256 color) BMP files provides a better color palette, depending on the total number of colors involved, and the method you use for color reduction. Some images work best with one method, other images work better using something else.

FS reads these just fine.

Hope this helps,

 

[sfrenchie]

They may have a simple .bmp extension, but they are all compressed images! DXT3 is the compression used most often.

The only 24bit bitmaps used by FS is in the ..\panel folder where the 2d panel images are kept.

I might be wrong but those don't look compressed. They are in ...\Flight Simulator 9\Texture and used for generic building by FS. Now I'm not sure if they are 24bit or else.

View attachment 9571

 

[n4gix]

Okay, I was a bit too broad and generalized in my assertion. Those are 8bit Indexed bitmaps, which obviously FS9 and FSX both can load.

Come to think about it, even the 24bit .bmp files used in the panel system are converted by FS to 8bit Indexed "on the fly" as they are loaded...

 

[arno]

Btw, about the DXT compression errors, I forgot this link:

http://fsdeveloper.com/wiki/index.php?title=DXT_compression_explained

In that Wiki article I have some pictures that show how wrong the colour can get because of the compression. Although that only happens in extreme situations.

Mixing different texture types can cause blurries, so in general it is advised to make all textures DXT compressed with mipmaps.

 

[sfrenchie]

Wow, excellent article. Thanks Arno, suddenly it makes everything so much clearer to me. On the same article I followed the link to how to make transparency in Photoshop. In 10 minutes I became much smarter about DTX format.