RE: [APML] OT: Tricolor Mars Images - Follow-up

["Lane, Jason R" <jason.lane@navy.mil>]

Hi guys,

The sticker might have a pink cast to it because of the color of the sky there (reddish).  A white sticker here under a blue sky may be a pink sticker under a red sky.  Although..you would expect that white sunlight is white sunlight no matter where you're at.  Maybe under bombardment of solar radiation during the journey there, JPL stickers turn pink.  :)

-Jason Lane


-----Original Message-----
From: Chuck Vaughn [mailto:aa6g@aa6g.org]
Sent: Tuesday, February 03, 2004 8:15 PM
To: Discussion of Film Astrophotography
Subject: Re: [APML] OT: Tricolor Mars Images - Follow-up


Hi George,

This is a good question and it may have to do with the way they are 
taking the images. I think it should be white too but it's not possible 
to have it white and not have blue rocks. You can have it one way or 
the other. :-)

I'm playing with another image with really blue rocks. It seems to be 
impossible to get rid of the blue without making the soil a brilliant 
red.

I'm sure a lot of thought went into taking the correct exposures for 
the science mission and that very probably has nothing to do with 
making nearly true color images. The various filters are called 
"geology filters." If true color was a science goal they probably would 
have had a standard set of 100nm wide RGB filters.

If we had the exposure times for each image we could create a 
calibration for each image but we don't. The easiest way to fix the 
problem is to set the soil to a reasonable color and then select all 
the blue and desaturate to some pleasing gray level. :-)

Chuck

--------------------------

> Hi Chuck
>
> I had a look at the image, looks quite good (OK, excellent) but a
> thought came to mind.
> Could one safely assume that the background of the JPL sticker would be
> white? I realize that if everything around is red that the white will 
> be
> a bit on the pale pink side. But could you not use the sticker as a
> white reference while trying to colour balance?
> I am sure that there is a serious flaw in my thinking but being a 
> newbie
> it escapes me.
>
> George Anderson
> Montreal Canada
>
> Clear skies and good health
>
> Chuck Vaughn wrote:

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