Re: [APML] Picture Resolution For Web

[Chuck Vaughn <aa6g@aa6g.org>]

Eddie,

The final size of any JPEG file is dependent on how much variation 
there is in the image. This means how noisy the image is, how much 
detail there is, how many stars, etc. There's no automatic size that an 
uncompressed image will compress to. It is image dependent.

Most likely, everything else being equal, the CCD image is less noisy 
than the film image and therefore compresses more than the film image.

I've noticed that images filled with stars don't compress well at all.

Chuck <aa6g@aa6g.org>

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

> Hi All
>  
> I think this may have been covered in the past, but I can't find much 
> on it.
>  
> What (and I'm sure you'll all have different answers) is the 
> "recommended" resolution for astro pictures to display on the www.
>  
> I'm using PS6 and have final film images approx 56MB (16 bit) at about 
> 3800x2550 and final ccd images approx 4MB and 1300x850
>  
> The reason for asking is that I can display a ccd image at, say, 
> 1000x???, and image looks fine (using the medium option for quality 
> under "saving images for the web"in PS when converting to JPEG) and 
> file size is around 100Kb, but if I do that with a film image (reduce 
> size to 1000x???), converting to JPEG produces a file size of over 
> 200Kb.
>  
> Should files  which are the same size (1000x???) be the same size 
> (100Kb)?? or am i doing something wrong.
>  
> If I reduce some film pictures (especially wide field), to 1000x??? 
> and reduce the file size to about 100Kb (using the low quality option) 
> the image looks like it's set in jelly!!
>  
> Help and/or advice appreciated
>  
> Thanks
>  
> Eddie Guscott



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