Help From The Celestia Oldtimers

[Don. Edwards]

Ok guys and gals,

I am going out on a limb here one old timer to the other old timers. Does Celestia still support a specmap placed in the alpha channel of a texture? If it does, is it less memory intensive than a stand alone specmap? The reason I ask is that for smaller texture releases I am considering going back to the practice of imbedding the specmap to make installing them easier. Also as of late, for some reason, my specmaps are not working properly. They smear across the surface or only half of them seem to appear and work at all.

I know full well that standing procedure is to look through the forum for this info, but we are talking of over 4 years worth of posts to try and go through and Celestia has gone through some significant changes over the years. So I want to make sure this feature still functions. I have yet to install the newest build so I haven't tried this myself. Any help would be greatly appreciated.

Don. Edwards

[Malenfant]

ooo, now that would be damn useful! What file formats support that? IIRC png does, are there any others?

[t00fri]

Ok guys and gals,

I am going out on a limb here one old timer to the other old timers.

I am one of the "oldest timers" but you havn't been going to me ...

Does Celestia still support a specmap placed in the alpha channel of a texture?

Certainly. Just have a look at the official /default/ earth.png texture in the Celestia distribution. There we have added the specmap to the alpha channel to save memory.

Bye Fridger

[Don. Edwards]

Hey Fridger,

You said the magic word, save memory. So I will be giving this a try and testing for any speed changes, thanks. I figured you would be the one to give me the right answer. I just don't like pinning anyone down and forcing and answer. I like the more passive approach.

Malenfant,

Both PNG and DDS support having the specmap in the alpha. I just haven't done it for so long I wasn't sure it was even still supported. I am glad to here that it is. So I guess I will be giving The Gimp a real workout.

Don. Edwards

[t00fri]

Hey Fridger,

You said the magic word, save memory. So I will be giving this a try and testing for any speed changes, thanks. I figured you would be the one to give me the right answer. I just don't like pinning anyone down and forcing and answer. I like the more passive approach.

Malenfant,

Both PNG and DDS support having the specmap in the alpha. I just haven't done it for so long I wasn't sure it was even still supported. I am glad to here that it is. So I guess I will be giving The Gimp a real workout.

Don. Edwards

An obvious addendum to DDS:

With alpha, DXT3 format is a must, since DXT1 (like JPG) does not support an alpha channel. While DXT1 compresses like 8:1, DXT3 only compresses like 4:1, i.e. will be double in size on the HD. But as to card memory, it does not make a difference if a texture with or without alpha channel is loaded! So in this respect you get the spec map for "free".

Bye Fridger

[Malenfant]

While we're on the subject, maybe you can explain something to me about these PNGs... why is it when I look in Photoshop (version 7) at the earth.png, all I see are the oceans? The continents look like they've been 'cut out' of the map - there's no colour on the land, all I see is the checkered background image. Is there an earth land map I'm missing?

[Rassilon]

While we're on the subject, maybe you can explain something to me about these PNGs... why is it when I look in Photoshop (version 7) at the earth.png, all I see are the oceans? The continents look like they've been 'cut out' of the map - there's no colour on the land, all I see is the checkered background image. Is there an earth land map I'm missing?

Thats because photoshop isnt the best at handling alpha on certain formats...In CS they have improved this a tad but its still buggy...eg: saving a TGA file without flattining layers in 32 bit will cause the alpha to become completely white...

Don..In case you forgot how to set up a spec map png in Gimp its done by exploding the rgb into 3 seperate greyscale images then right clicking on the spec map and composing an RGBA image adding each red green and blue maps to thier proper slots...Then the spec map as the alpha...

[steffens]

why is it when I look in Photoshop (version 7) at the earth.png, all I see are the oceans?

This is because the specular map is stored in the alpha channel, which is normally used to represent transparency. Land masses don't reflect a lot of specular light, that's why these regions are transparent. You can disable the (display of the) alpha channel in Photoshop to see the raw texture data without transparency.

steffens

[Malenfant]

why is it when I look in Photoshop (version 7) at the earth.png, all I see are the oceans?

This is because the specular map is stored in the alpha channel, which is normally used to represent transparency. Land masses don't reflect a lot of specular light, that's why these regions are transparent. You can disable the (display of the) alpha channel in Photoshop to see the raw texture data without transparency.

How do you do that? When I look at the channels for the earth.png all I see are the usual RGB ones, I don't see an alpha channel. And the only layer there is 'layer 0'.

[ajtribick]

On the subject of specmaps, it would be nice if there were some way to control how the specular maps are loaded. I'm currently using some high res Earth maps (I think they're Don Edwards's maps), and they have a separate specmap. However activating the specmap option in solarsys.ssc causes the high res specmap to be loaded when using medres textures (which I use fairly often when I'm testing stuff, as it greatly improves load time), because there isn't a specmap in the medres folder.

So I've basically ended up extracting the alpha channel out of earth.png into a separate file in the medres folder.

[Don. Edwards]

Hey Rassilon,

It?€™s been a long time hasn't it. I absolutely remember how to add the specmap, its somewhat similar to making transparent clouds in GIMP. Although I have moved to Paint Shop Pro for all my cloud making, I still use Gimp for many things. Mainly because it allows for the adjustment of compression on PNG files.

To everyone else, I too have run into that darn problem with Photoshop CS wrecking TGA files. There is another work around though. Take the TGA file format plug-in from Photoshop 7 and replace the one in CS with it. This solves the transparency issue once and for all.

On a side note, I was going to move to Photoshop CS2 (9), but they had the short sightedness to remove the layering check boxes that were in the previous builds. This makes the way I work in Photoshop totally useless as I now have no control over adjusting what layers I want to merge or turn on and off.

Ok that?€™s a little off subject. But all my new textures will be going back to having the specmap in the alpha channel. If it gets the free ride that Fridger says it does this is a no brainer. That will also save from having to add the parameter in the .ssc files as well.

Don. Edwards