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48bit Scanner Resolution and PS Questions

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  #1  
Old 08-10-2006, 06:12 PM
Lucile Davis Lucile Davis is offline
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48bit Scanner Resolution and PS Questions

I read the following (http://www.scantips.com/ -- head swimming ), and searched the forums but could not find the answers to specific questions about scanning resolution and PhotoShop.

My 16bit scanner scans at the hardware resolution of 600ppi max. Lusting after a 48bit scanner here -- what is the highest non-interpolated resolution at which I can expect to scan? The scanner spec sheets obfuscate this saying things like 4800 x 9600. Is the actual max resolution 4800?

My ultimate need is to offset print images at 300dpi, hopefully as large as 30" x 40" onto paper, using transparencies (slides and 4x5s) for input.

The next question is can the most recent versions of PS software handle 48bit images? Does it matter which choice from PS7, CS, or CS2? In other words, do the newer versions handle 48bit images better than the earlier ones?

TIA
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Old 08-10-2006, 06:58 PM
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Littlecoo Littlecoo is offline
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Insofar as support for 48bit images goes, CS2 is best and most flexible for importing and working directly with 48bit (16bit/channel) mode. CS supports import of 48bit images but working directly in this colour mode is much more limited.
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Old 08-10-2006, 07:05 PM
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mistermonday mistermonday is offline
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Scanning

Lucile, welcom to Retouch Pro. Scanner manufacturers do tend to make things confusing. The image files do not actually have word data length of 48 bits. Each pixel in an RGB image is defined by 3 16 bit words, one each for the red, green, and blue channels. Older scanners used to only generate 8 bit words and used to call their scanners 24 bit. Then as electronics and optical sensors improved they went to 12 bits (36 bit scanners), then to 16 bits.
Earlier versions of PS (I think prior to 5.0) could only process 8 bit images. As PS went thru each successive version, more of its filters and adjustments could handle 16 bit images. CS2 allows you to execute most commands on 16 bit word length.
Check your scanners specs for Optical resolution. Any manufactured in the past 6 years should be at least 1200 dpi. Anything higher than optical resolution means the rest of the data is interpolated.
Finally, don't confuse the bit depth of an image with the scan resoltion and print size. For example, if you want to scan a 35mm slide and print it at 8 x 10 @ 300 dpi, your image dimensions (without resampling) will need to be 2400 x 3000 pixels. Since your 35mm slide is 1 x 1.5 inches, you will need to have a scan at 2400 dpi to get the amount of data you need for the print.
This has nothing to do with the fact that the pixel data can be 8 bit or 16 bit. I hope this helps.
Regards, Murray
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Old 08-10-2006, 10:05 PM
Lucile Davis Lucile Davis is offline
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A Follow-up Question

Thanks for the very helpful insights.

A further question: The 300ppi scans from my existing scanner show striations or very close together fine lines across the face that can be seen when viewed at 100% resolution on a monitor. (They do not show on an inkjet printout, but I suspect if sent to an offset press would be visible.) Can I expect better from a 48bit scanner, or are the fine lines the nature of all scanners?
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Old 08-10-2006, 11:25 PM
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mistermonday mistermonday is offline
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Lines

Lucile, scanners (even the low end inexpensive ones) usually pick up all of the very fine lines and other anomalies in a scan that people do not see with the eye unless they zoom in real close or use a magnifying glass. You should inspect the original scanned photo or document to first ascertain if the lines or texture are in the original. If they are, then there are techniques to remove them in PS or to at least minimize them. Hoever, if those lines are not present in the scanned material, then you may have one of a number of other issues. It might be useful for you to upload a small sample of the image so we can take a look at it.
Regards, Murray
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Old 08-11-2006, 08:54 AM
xvvvz xvvvz is offline
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Hi Lucile - You will get better answers if you provide more specific information about the materials you are scanning, the scanning software and settings used and what scanner model you are using. There are just so many variables that it is hard to provide well targeted suggestions unless this other information is known.

Doug
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  #7  
Old 08-11-2006, 03:20 PM
Lucile Davis Lucile Davis is offline
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Re: Fine Lines in Scans seen at High Zoom

Thanks for the suggestion.

Attached is an image file scanned at 600ppi in which fine lines can be seen on a monitor in PhotoShop at 66%, 200%, and 300%. The scan was made from a 4x5 (large format) photo transparency taken of an original pastel artwork that had no lines or dots in it.

The question: Are these fine lines a quirk of my current 24bit scanner, and can I hope for better if I acquire a 48bit machine, or is it something that occurs in all scanners? The concern is that they will be apparent when commercially printed at 300 dpi on an offset press.

Enlarge the image to 66%, 200%, and 300% to see the defect.

TIA
Attached Images
File Type: psd RetouchPro600ppiSample.psd (80.6 KB, 16 views)
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Old 08-11-2006, 04:50 PM
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mistermonday mistermonday is offline
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Scan Lines

Lucille, firstly your sample is microscopic (only 16KB). Your attachment can be 100KB. So it is very difficult to tell from your small sample, but I removed the color noise and it appears to me that the pattern remaining appears to be texture - as in a canvas or textured art paper. Was the orig paper textured?

If not, then I would turn to the scan next. Did you use a dedicated Slide / Negative scanner or did you scan the transparency on a flat bed? If it was a flat bed , did it have a special transparency adapter? Finally, was your 4x5 a positive (slide) or a negative film?

Regards, Murray
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Old 08-11-2006, 06:44 PM
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Littlecoo Littlecoo is offline
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Okay, I have posted here a couple of examples of a scanner issue that I have experienced when scanning at high res and bit depth (FYI...a photo print in an early model HP flatbed scanner) the higher the scan resolution, the more severe the banding it get progressively finer and closer together like the effect I noticed along the left edge of your sample(sorta starts to resemble clear glass louvres lol). Is this anything like what you are experiencing Lucille?
Attached Images
File Type: jpg scanner_banding1.jpg (97.7 KB, 11 views)
File Type: jpg scanner_banding2.jpg (95.8 KB, 10 views)

Last edited by Littlecoo; 08-11-2006 at 06:57 PM. Reason: add more info
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  #10  
Old 08-12-2006, 03:49 PM
Lucile Davis Lucile Davis is offline
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My sample was originally huge, but the forum would not take it. When it got to 80K in PS, it was finally accepted. Have no idea why it is only 16K now.

The lines are horizontal, and can be seen in PhotoShop. Open in PS and enlarge to 66%, 200% and 300%. Oddly, they do not show at 100% resolution. They are easier to see in the dark areas of the sample.

They do not resemble the previous samples, Littlecoo. But thank you for taking time to compare.
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