Celestia Forums

OK, I'm back from a long search in the forum and documentation in search for a reply to a few questions. I found none, which may mean that I simply didn't search in the right place. So, I'm asking.

First of all, JPGs. When I output my image as JPGs I get quite a bit of compression artifacts. It seems that the JPG definition is not very high by default, and the inevitable question is: is it possible to change it?

Secondly: image sizes. After experimenting a bit, I got to the conclusion that the only thing that affects the size of the oputput image is screen size. Is this true, or is there any other way to change (enlarge, mostly) the default? I see humungous pictures all around the forum and get a bit frustrated by the 730 pixels of height I can squeeze in my pityful efforts...

(I went around poking my nose in stuff like the cfg file and all that... didn't see anything that hinted at a solution)

Jorge,

JPEG images have artifacts. How bad they are is determined by how much compression was used when the original texture image was created. The 3D card adds a small amount of artifacts, too. If you want the least artifacts you need to use PNG textures, which have no compression at all. DDS are in between: they have artifacts, but usually not as bad as JPEG.

Celestia can only do screen dumps. The 3D graphics card creates the images. Celestia's images are created at the resolution of your screen. If you want to create higher resolution images, your display has to be set at that resolution. You may need to upgrade your display if you want to create larger pictures.

selden wrote:JPEG images have artifacts. How bad they are is determined by how much compression was used when the original texture image was created. The 3D card adds a small amount of artifacts, too. If you want the least artifacts you need to use PNG textures, which have no compression at all. DDS are in between: they have artifacts, but usually not as bad as JPEG.

I know fairly well how JPG works, ditto for PNG, although I'm relatively blank with regard to DDS. My question was not about how those artifacts appear, but about the possibility to decrease the default level of JPG compression (that has to be programmed in the file-creating routines) in order to decrease JPG artifacts.

selden wrote:Celestia can only do screen dumps. The 3D graphics card creates the images. Celestia's images are created at the resolution of your screen. If you want to create higher resolution images, your display has to be set at that resolution. You may need to upgrade your display if you want to create larger pictures.

Now that's unfortunate. I can see why it was programmed that way (you don't have to re-render the image before saving), but it's a bit annoying. Heck, it's very annoying!

Thanks anyway.

Jorge wrote:

selden wrote:JPEG images have artifacts. How bad they are is determined by how much compression was used when the original texture image was created. The 3D card adds a small amount of artifacts, too. If you want the least artifacts you need to use PNG textures, which have no compression at all. DDS are in between: they have artifacts, but usually not as bad as JPEG.

I know fairly well how JPG works, ditto for PNG, although I'm relatively blank with regard to DDS. My question was not about how those artifacts appear, but about the possibility to decrease the default level of JPG compression (that has to be programmed in the file-creating routines) in order to decrease JPG artifacts.

selden wrote:Celestia can only do screen dumps. The 3D graphics card creates the images. Celestia's images are created at the resolution of your screen. If you want to create higher resolution images, your display has to be set at that resolution. You may need to upgrade your display if you want to create larger pictures.

Now that's unfortunate. I can see why it was programmed that way (you don't have to re-render the image before saving), but it's a bit annoying. Heck, it's very annoying!

Thanks anyway.

Jorge,

I don't see the point you are trying to make.

I have published innumerous high-quality screenshots with Celestia during the last fours years in the forum. What I do is to first save interesting configurations as /lossless/ PNG's . Then I quickly start GIMP and crop,/cubically/ rescale and merge the various images. Finally I save them as 85% quality , 1x1,1x1,1x1 subsampling with floating point DCT method. The quality of my images is very high indeed with file size being still quite moderate. To upload the results to Chris' server in Seattle just takes me one short shell script command:

> chris <files.jpg>

I would be absolutely stupid to integrate such advanced image manipulation methods into a program like Celestia, that definitely needs its resources for other purposes. Being an expert in image manipulation techniques, such a task never takes me longer than ~2 minutes, starting with fresh PNG screendumps until the point when people can look at the results in my forum posts

Here you find some recent examples of this very fast high-quality approach:

http://www.shatters.net/forum/viewtopic.php?t=7619&postdays=0&postorder=asc&start=25

Bye Fridger

Fridger,

[edit]after rereading your posting, it seems you were responding to Jorge's first question rather than the second, but what the heck...[/edit]

There are some applications where it would be useful to have Celestia create very large images -- 4K x 3K or even larger. In principle it should be possible to link Celestia to a software OpenGL library that could write such large files. But I doubt that'll actually happen.

Hang on. So you're telling me that those are enlarged after the dump?

Hum... if that's the case, then I surely see your point.

Just out of curiosity, how large are the images your dumps produce? I can't get past 730 pixels of height myself, although that might change once I get a new graphic card.

Jorge wrote:Hang on. So you're telling me that those are enlarged after the dump?

Hum... if that's the case, then I surely see your point.

Just out of curiosity, how large are the images your dumps produce? I can't get past 730 pixels of height myself, although that might change once I get a new graphic card.

1600x1200

t00fri wrote:1600x1200

I thought so. And that makes all the difference in the world. With a starting point that is almost twice as large, even with the same image treatement the end result is inevitably twice as good.