Newbie: Guidance sought on when to choose 24-bit color vs. 48-bit color.

DC
Posted By
D_C_G
Aug 20, 2004
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What image characteristics of a photograph, slide, or negative determine when it should be scanned at 16 bits per color channel (48-bit color) instead of 8 bits per color channel (24 bit color)?

I have three image-editing programs that I’ve been using for several years: Adobe PhotoShop Elements 2.0, Adobe PhotoShop Home Edition 4.0, and Jasc Paint Shop Pro 7. After some tests, it appears that all three only support 8 bits per color channel (24-bit color). I’m trying to decide if I need to purchase another image editor to get 16 bits (48-bit color).

My present goal is to archive old family photographs (1890-present), slides (1950-1980), and negatives (1910-present). Images from about 1970 to present were taken by amateurs. Prior to 1970, some photographs and negatives (not slides) were taken by professionals.

I’m using an Epson Perfection 4870 flatbed scanner for the photographs and larger (4"x 5") negatives. I hope to use a Nikon Coolscan V for the slides and smaller negatives.

I’d appreciate any guidance you can provide as to how much color resolution I’m likely to need for this archiving.

Thanks for the help,
DCG
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MM
Mac_McDougald
Aug 20, 2004
Endless debate re just how effective 48 bit scanning really is. Histograms prove that many editing functions are much less "destructive" done in 48 bit. Eyeballs prove that the difference is negligible to non- existant on most images.

One things for sure, film may benefit from high bit editing, but it’s a waste on flat copy, the information just isn’t there to waste the file size on.

Also also, most advanced scanner folks would say that 48 bit from a flatbed, even from film, since your Epson has nowhere near the actual resolving power of dedicated film scanner at same ppi, would generally be a waste of time and disk space also.

Of course, just prove it to yourself. Make a 24 and 48 bit scan of several film examples, and put each through the same editing functions you ever expect to use, then compare final examples on screen and on print output to see.

Of course, one should always SCAN in highest bit depth your scanner offers, even if just saving as 24bit. That’s where the biggest gain is, letting the sampling algorithm select the best of the high bit sample from which to compile the 24 bit file.

Mac
MM
Mac_McDougald
Aug 20, 2004
Oops, sorry…see you don’t have anything to edit 48 bit WITH, as far as my suggestion for doing your own comparison.

You could download Photoshop CS tryout and get with it for the 30 days or so it allows.

Or just not worry about it. IMNSHO, it’s not worth it, certainly not from flatbed, even one as capable as that one.
But you can search Google Groups Usenet archives for the subject in comp.periphs.scanners, or ask there directly yourself for other opinions.

Mac
DC
D_C_G
Aug 20, 2004
Thanks for the input.

One more question: your comments were aimed at the flatbed scanner. I’m also planning on using a film scanner (Nikon Coolscan V). Do your comments still apply to this scanner (and slide/negatives from pre 1970s)?

thanks,
DCG
TL
Tim_Lookingbill
Aug 20, 2004
I can give you a basic understanding of what bit level is. This will help you decide if it’s important for your situation.

Bit level is a measure of how many DIFFERENT levels and how MUCH of tonal information that can be captured off a device. The differences determine the illusion of depth in an image. You can see the amount of difference by dragging your cursor and watching the info palette over an area of an image that seems to be one color like in a blue sky at sunset or fleshtone. The faster the RGB numbers change constantly tells you the amount of differences captured. How much can only be determined after you edit and save the image and what’s left over.

The amount of differences captured will be determined by the subject matter, quality of lens, CCD chip and software driver capturing the image.

The more severe you have to edit those differences, the more you will lose the amount of differences leading to posterization and enhanced noise the more you edit.

Even if you don’t plan on doing much editing, it’s always best to capture at the highest bit depth and optical resolution your device can give. You can always keep it as a master file like an archival digital negative to work from for future use.

Besides you paid good money for the device why not use it to its full extent.
MM
Mac_McDougald
Aug 20, 2004
Nikon V is a whole ‘nother level of quality.
REAL 4000ppi, resolves many more line pairs in actual rez than your Epson, greater dynamic range, shadow detail, every aspect of scan better any way you look at it.

In case of this device, it certainly WILL capture meaningful 48 bit information. However, 24/48 bit digital jihad continues. About half of even pro imaging folks will still say 48bit is negligible diff at best with at least the most common editing functions.

Again, you can settle into Google Groups archives and read the pro/con on the subject for a few days and decide.

Of course, if you have the storage space, why not archive 48 bit? (I don’t though).

Mac
CW
Carl_Wegner
Aug 21, 2004
You can’t see any difference on screens (really a display card limitation not screen) or consumer printers since they are all 24 bit. Any 36/48 bit file will be truncated to 24 bit when sent to display or printer. If 36 or 48 bit display cards and printers become available someday the difference in dynamic range (tonality / shades from white to black) will be clear. I don’t trust there will ever be better cards/printers, so I don’t bother with 36/48 bit either for final storage.

I do think my Polaroid 4000 scanner working in 36 bit mode, followed by its software doing an initial levels adjustment in 36 bit mode, followed by final output to a 24 bit file provides much better images than if I leave out the Polaroid levels step and do all levels in PS.

Carl

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