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Re: filmscanners: Re: Hello, thanks, and more.



Comments are below:

Maris

----- Original Message ----- 
From: "Ken Durling" <kdurling@earthlink.net>
To: <filmscanners@halftone.co.uk>
Sent: Sunday, October 21, 2001 10:53 PM
Subject: filmscanners: Re: Hello, thanks, and more.


| HI all - 
| 
| And thanks very much!   Whew, I've read through the posts 3 times now,
| and the two immediate questions that are coming up are:
| 
| 1) Bits.  I need some clarification on what the siginificance of all
| the different bit-rates are about for color.  For example,  one person
| mentioned that there is no real advantage in 16-bit over 8-bit color
| for printing.  Someone else mnetioned "editing in 16-bit."   The Canon
| software only offers scanning in 24-bit color, unless I initiate the
| scan from within Corel Photo House, in which case I get an option of
| 36-bit color, as well as a different set of RGB, Gamma and
| Brightness/Contrast dialoques. ( I notice this 36-bit option results
| in a nearly 60MB file for a 35mm slide, as opposed to 28.9 for 24-bit)
| Vuescan seems to default to 48-bit color.  So I'm a bit confused.  I
| don't recall this coming up when I was scanning with HP Photosmart
| with my 5200C.  

I don't know what Corel Photo House's 36-bit color is, but the basic argument 
is whether it is better to adjust images, before sending the image to print,  
in 16-bit or 8-bit color.  Inkjet printers accept only 8-bit color, meaning 8 
bits per RGB channel and therefore 24 bits total, so you will have to send an 
8-bit per channel image to the printer for printing.  Vuescan and other 
scanning software will scan at 16 bits per channel, which when cubed results in 
a much larger number of colors than 8 bits per channel cubed (but adding the IR 
(infra-red) channel it would be 64 bits).  Theoretically, 16 bits per channel, 
providing for more color gradiations, allows for more subtle and accurate color 
adjustment.

Whether in the real world it is preferable to adjust image colors using 16 bits 
per channel rather than 8 bits per channel has been a long standing argument.  
I refer you to Dan Margulis's thread in the Color Theory group at 
http://www.ledet.com/margulis/ACT_postings/ACT-8-bit-16-bit.html and to Bruce 
Fraser's article at http://www.creativepro.com/story/feature/7627.html

| 2) Sizing.  Now this is just specifying the pixel dimension of the
| image, correct? Without changing the resolution.   Someone mentioned
| "resampling" and "downsampling."    For example, I scan a slide at
| 2720 dpi, and I get a 28.9 MB TIFF file that measures something like
| 3889x2550 pixels.  After adjusting color and brightness, etc, and
| saving,  I go into the properties dialogue and specify a web-based
| size, i.e. about 750 pixels in the longest dimension. Is that
| "downsampling?"  Is that process in itself "lossy?"  

Yes, that is downsampling.  I refer you to 
http://www.scantips.com/basics02.html and the sections before it and after it - 
Wayne Fulton explains these concepts well.

| I have yet to run into TIFF LZ compression, I must look further, but I
| don't recall that as an option.

It is LZW compression - it is an option in Photoshop and in Corel PhotoPaint - 
I don't know whether it is an option in Corel Photo House.

| In any case, as a result of reading your advice I am now:
| 
| Always scanning at max res, ie 2720 dpi.  

Excellent!

| Saving my uncompressed TIFF files to a CD.  (I Ihave a Sony 16x and
| the Adaptec v.4 software)   This is simple because when I do the scan
| I save the TIFF into a directory, and then open it there with a
| graphics app and create, for example, a jpeg to send to my web
| portfolio.  This leaves the TIFF untouched, and I send that to a CD
| and delete it off my hard disk.  

Also excellent - archive your original scans untouched.  You may at some point 
want to print them, which calls for a higher resolution, and with practice you 
may end up with a better looking image.





 




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