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Re: (meteorobs) OT: Film for comet photos

On 10 Jul 2001, at 8:14, Robert Warren wrote:

> It is interesting that some people are using such software packages as 
> "photshop".  However, in cometary astronomy, there are two basic problems in 
> doing so.  The first is if you manipulate the color of the image, you could 
> be losing valuable information. 

Actually information is not "lost" at all! By enhancing the color 
levels, you are just removing the zero bits above and below the min 
and max pixel values in the 3-color histogram. The resulting pixel 
values (the real information) are then expanded to fill the entire 24 
bit (3color x 8bit) dynamic range of the digital image. So, rather 
than lose information you simply display what is already there in a 
fashion that is better visible to the human eye.

> The color of the comets tail, or coma, or 
> even nuclear region are indicative of what parent moecules are being 
> released from the nucleus.  The Color response of the film can detect only 
> certain molecules, because each and evey molecule can only emit certain 
> wavelengths of light, or spectral lines.  So the color response of the film 
> is very important.  

Thats the reason why you want to process the color balance of the 
overall image to be as "true" as possible. It will then bring the 
colors in the coma nd tail more closely to their actual one, not 
biased by whatever inherent limitations in the chemical response of 
the analog emulsion.

> It is obvious that you do have some understanding of the 
> problems with grain.  However, with the newer color films as with the older 
> versions, grain is not a factor considered in a color film, since the latent 
> image taken upon exposure, is replaced by chemical dyes during the 
> development process.  (Reference any Kodak color film manual, or data 

Higher speed color films are definitely more grainy and lower 
resolution than the lower speed films. This is still a property of the 
manufcturing process of the emulsion. You cannot eliminate grain 
by development process alone!
 
> lose imformation.  So how sure are we that the image that you manipulate is 
> what was actually there?

Again, no information is lost in enhancement, so you simply see a 
better representation of what is really there, not dynamic range 
limited by the background noise or color shifted.

Happy imaging!
Mike

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