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[OM] Re: Good K64, butchered XP2

Subject: [OM] Re: Good K64, butchered XP2
From: Moose <olymoose@xxxxxxxxxxxxxxx>
Date: Wed, 08 Jun 2005 20:40:07 -0700
Earl Dunbar wrote:

>I ordered develop only and high res scan... "16-base" scans, whatever that 
>means.  
>
That should mean that the full dynamic range of the scanner, probably 14 
bit per color per pixel, is delivered to you. Because of the way 
computers work in bytes, if you don't go to some trouble, it is 
delivered in two byte chunks, 16 bits, per color per pixel.

>The resulting JPGs are anywhere from 2.5 to 4.3MB.  
>
This is where you should know you've not gotten what was represented. 
The JPEG format only accomodates 8 bits per color per pixel. Thus, you 
did not get the "16-base" scans. They would have come in another, 
non-lossy format, probably TIFF, maybe BMP.

><>
>Sorry for the long post, but I had to vent a bit.  But I do have two 
>questions:
>
>1.  What accounts for the variable file sizes of the XP2 scans?  I mean, 
>every frame is a full 35mm frame.  Is this related to overall negative 
>density, or with scanning technique or settings?
>  
>
As Wayne and Chuck said, it's the nature of JPEG. The more small detail, 
the larger the file.

>2.   I assume that since I got JPGs, and from a non-custom service, I 
>really can't judge the dynamic range of the files as being best 
>possible.  
>
Correct. The output from the scanning mechanism has to be compressed 
into a smaller brightness range. This may involve both throwing away 
some of the highlight and shadow detail by a combination of clipping and 
compression and compressing the dynamic range overall. Film can capture 
considerably more brightness range and detail than can be represented by 
8-bit scans.

>One some of the shots with wide tonal range, the highlights 
>are blown.  Even on the negs they look like they may be blocked under a 
>low power loupe, but I can't be totally sure.  Any insight?
>  
>
It may or may not be the film. I have paid for scans that have been 
fine, then others from the same place with highlights blown out. 
Subsequent scans with my own scanner showed that the highlights were 
fine on the film and could be scanned just fine. I mean really, it takes 
something pretty bright to blow the highlights on color neg film.

>3.  If I find that the highlights are actually blown on the negative, 
>might this be an indication of exposure error?  
>
I believe that is in fact the definition of exposure error.

By the way, a scanner with infrared hardware based dust removal should 
also remove most of the scratches.

Moose


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