This is Selden's colortest for Celestia

Contents

0: Introduction.
1: Comparisons of Color Images.
2: Comparisons of Color Histograms.


A.0: Appendices.


A.1: Signature.
A.2: Admonishment.
A.3: Disclaimer.


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See also:
• Selden's List of Resources for Celestia

0: Introduction.

Recent discussions on the Celestia Web forum of the relative quality of the differnt types of surface texture image types made me decide to do some quantitative tests.

Sadly, my conclusion is that the colors in the displayed images are being badly damaged. What I don't know is what is causing the damage: Celestia, OpenGL or the display hardware.

Update: 22Mar2004:

The color problem is caused by the 3D modelling software that I use. By default, Anim8or's models specify material values of

---

     diffuse {
        rgb { 224 224 224 }
        factor { 0.70000 }

---

After replacing these by

---

     diffuse {
        rgb { 255 255 255 }
        factor { 1.0 }

---

the damaged color values were fixed.

Description of test system:

• 256MB 500MHz P3, Windows XP SP1
• 128MB GeForce4 Ti4200, drivers v56.55, OpenGL v1.5.0
• Screen color adjustments with default settings:
  • Digital vibrance off
  • Brightness 100%
  • Contrast 100%
  • Gamma 1.0
• Celestia v1.3.2pre7
• nvDXT v6.31

Testing on a P4 system with an Nvidia FX5200 and drivers v53.03 yielded identical results.

Description of test procedure:

1. download NOAO's 5477x5610 91MB (lossless) tiff image of the Eagle nebula from http://www.noao.edu/image_gallery/html/im0725.html
2. convert the tiff image to (lossless) 91MB ppm format
3. downscale ppm image to 1999x2048 12MB ppm
4. pad sides to make it 2048x2048
5. convert 12MB ppm to (lossless) 12MB tga
6. convert 12MB tga to (lossy) 2.7MB DXT1c, 5.4MB DXT3 and 5.4MB DXT5 using nvdxt (default nvdxt settings used)
7. convert 12MB tga to (lossless) 16MB U888 using nvdxt (default nvdxt settings used)
8. convert 12MB ppm to (lossless) 7.8MB png and (lossy) 540KB jpg using ImageMagick convert
9. run Celestia with each of the five texture file formats
   • Use a Cel:// URL to guarantee the same viewpoint each time
10. take Celestia screenshot into (lossless) png format
11. convert png images to (lossless) ppm
12. use pnmhistmap to create color histograms, showing the counts of the color values in the screenshot images.

1: Comparisons of Color Images.

colortest texture jpeg Jpeg colortest texture.

Difference between DXT3 and PNG colortest texture images The DXT3 and PNG surface texture images were each loaded into IrfanView v3.85, saved in (lossless) BMP format, and then compared using the ImageMagick command composite -compose Subtract colortest-dxt3.bmp colortest-png.bmp diffc3p.jpg

Celestia colortest screendump Celestia screendump showing the viewpoint of the test.

2: Comparisons of Color Histograms.

Colortest Texture Image colors	Celestia colors before model repair	Celestia colors after model repair
png texture's histogram Histogram of colors of the 8MB PNG surface texture image. Note sharp peaks of discrete colors.	Celestia png histogram Histogram of colors displayed by Celestia for the PNG surface texture convert tmp3.ppm tmp3.png	Celestia png histogram Histogram of colors displayed by Celestia for the png surface texture after repairing the 3D model's material values
u888 texture's histogram Histogram of colors of the 16MB u888 surface texture image. Note sharp peaks of discrete colors. just as in the PNG surface texture image.	Celestia u888 histogram Histogram of colors displayed by Celestia for the u888 surface texture nvdxt -file tmp3.tga -u888	Celestia u888 histogram Histogram of colors displayed by Celestia for the u888 surface texture after repairing the 3D model's material values
original jpg histogram Histogram of colors of the jpg surface texture image. Note smoothing done by jpeg compression when compared to lossless PNG.	Celestia jpg histogram Histogram of colors displayed by Celestia for the jpg surface texture convert tmp3.ppm tmp3.jpg	Celestia jpeg histogram Histogram of colors displayed by Celestia for the jpeg surface texture after repairing the 3D model's material values
Histogram of colors in the DXT1C surface texture image	Celestia DXT1c histogram Histogram of colors displayed by Celestia for the DXT1C surface texture nvdxt -file tmp3.tga -dxt1c	Celestia DXT1c histogram Histogram of colors displayed by Celestia for the DXT1C surface texture after repairing the 3D model's material values
Histogram of colors in the DXT3 surface texture image	Celestia DXT3 histogram Histogram of colors displayed by Celestia for the DXT3 surface texture nvdxt -file tmp3.tga -dxt3	Celestia DXT3 histogram Histogram of colors displayed by Celestia for the DXT3 surface texture after repairing the 3D model's material values
Histogram of colors in the DXT5 surface texture image	Celestia DXT5 histogram Histogram of colors displayed by Celestia for the 5.5MB DXT5 surface texture nvdxt -file tmp3.tga -dxt5	Celestia dxt5 histogram Histogram of colors displayed by Celestia for the dxt5 surface texture after repairing the 3D model's material values

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Contents

0: Introduction.
1: Comparisons of Color Images.
2: Comparisons of Color Histograms.


Appendices.


A.1: Signature.
A.2: Admonishment.
A.3: Disclaimer.


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See also:
• Selden's List of Resources for orig

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[back to Contents]

A.0 Appendices.

A.1: Signature.

This Web page is maintained by Selden Ball at Wilson Lab.

A.2: Admonishment.

Please send any questions, comments or corrections to seb@lepp.cornell.edu
Alternatively, you can post a message (anonymously or otherwise) on orig's Web Forum or use its Private Message page.

If you don't tell me that something's missing, unclear or wrong, I can't improve it.

A.3: Disclaimer.

The author disclaims all liability and endorsement.
Copyrights may apply.
For details, please read the full text of his disclaimer.