Celestia Forums

Hi all,

This is a try to combine 3 Cassini raw images to a color picture of Phoebe. I avoid to say "true color" because the raw images are not validated/calibrated and the dynamic range of these images from Phoebe vary partly strong.



Have fun!
Jens

So it's grey, then ...

Grant

PS: And, without wishing to be picky and argumentative, don't you feel the same reservations about colour apply to what you've just called your "2k Saturn rings in true color"? I do honestly feel that's a misleading name, given the images used are as unvalidated and uncalibrated as those for the Phoebe image above.

granthutchison wrote:So it's grey, then ...

... maybe a little bit brownish.

granthutchison wrote:PS: And, without wishing to be picky and argumentative, don't you feel the same reservations about colour apply to what you've just called your "2k Saturn rings in true color"?

No, I don't feel so. Grant, there is a little difference between Phoebe and Saturn. There are some "official" true color images from Saturn rings on the net while I can't find such a thing for Phoebe. Further we know that the Saturn rings less colorfull and that means the red, green and blue channel aren't so different and they "should" use the same dynamic range. Another problem with Phoebe is that there are large albedo differences and Cassini optimice the data for transmission to 8 bit.

Jens

Fair enough. But to be fair you didn't mention any official true-colour Saturn images when you posted your new rings, only the Cassini raw data.
Did you then use these true-colour images to calibrate the intensity of your extracted colour data? Can you provide a link? That would be very useful.

Grant

granthutchison wrote:Did you then use these true-colour images to calibrate the intensity of your extracted colour data? Can you provide a link? That would be very useful.

I'm not sure what you mean.
What I did was to build a simple ring texture (only rgb) from a released picture (PIA06077) and used this to adjust the rgb channels (only linear) of the new (raw) rings. Further I'd noticed that a factor must be applied to correct the brightness for Celestia (all textures must be a bit brigther to appear right in Celestia).

That's all.
Jens

jim wrote:I'm not sure what you mean.

Sorry: I meant exactly what you say you did - using a "true colour" image as a reference to adjust the intensity of the colours in the raw images.

It's interesting that your reference image is described as "natural colour" - an earlier, identically coloured image was described as "contrast enhanced" on first release (and the original NASA information on this one called it "colour enhanced", too, though that URL is dead). But now, the same image is cheerfully labelled "natural colour". You have to wonder if NASA isn't using the term "natural colour" the same way the manufacturers of hair-dye do

Grant

granthutchison wrote:It's interesting that your reference image is described as "natural colour" - an earlier, identically coloured image was described as "contrast enhanced" on first release (and the original NASA information on this one called it "colour enhanced", too, though that URL is dead). But now, the same image is cheerfully labelled "natural colour". You have to wonder if NASA isn't using the term "natural colour" the same way the manufacturers of hair-dye do

I know this problem. It seems that NASA want to make pictures more beautiful by enhanceing the contrast and colors. OK, I used this picture principial to adjust the brightnes/contast of my raw rings in relation to Saturn.

I think I unterstand now: it's better to use the term "real color" instead of "true color".

Jens

granthutchison wrote:...
You have to wonder if NASA isn't using the term "natural colour" the same way the manufacturers of hair-dye do

Grant

h? h?...what about a zip of Laphroaig?

Bye Fridger