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Input/Output/Workflow Scanning, printing, color management, and discussing best practices for control and repeatability

Adjust pre or post scan?

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  #1  
Old 12-11-2007, 10:05 PM
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Doug Nelson Doug Nelson is offline
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Adjust pre or post scan?

In the Jan/Feb issue of Photo Techniques there's an article by Ctein titled "The Right Way to Scan". In paragraph three he states "All scanners collect extra value levels internally, and they are available to fill in any gaps in the histogram when you expand or compress parts of the tonal range". This is in reference to using levels or curves in the scanning software.

This is news to me.

Does anyone have any manufacturer data on this issue? If I understand what he is saying (and I probably don't), the scanner is either magic or holding back valuable data that we could be using.

Before anyone jumps in to say he's talking about 16bit vs. 8bit, no he's not. But I also know Ctein tends to know what he's writing about, so I'm honestly looking for expansion on this concept.

My own understanding of scans is that they're like raw files in a way, in that you get the raw data during the scan and then any adjustments are made after that point. This is true whether done in the scanning software or in Photoshop. If he's right, I'll need to rethink my scanning workflow.
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Old 12-11-2007, 11:08 PM
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Re: Adjust pre or post scan?

The scanner electonics basically take an analog voltage measurement off a sensor element and convert that measurement into a digital number. Whether the electronics can measure 1.257Volts versus 1.2568319 Volts determines the bit accuracy of the final output. Low end scanners used to have 10 bit A/D converters and as you go up they go to 12 and up to 16. What actually comes out of the scanner and into you computer is dependant on what the scanner's driver s/w does to the data. Unfortunately, the software wants to do too many favors for users (not always for altruistic reasons). They try to auto color, auto contrast, descreen, etc. When you turn all of that auto stuff off, what you get as output still depends on how much of the RAW data the scanner s/w is capable or willing to send you. Trade offs are file size, speed of data transfer and scan speed. It is certain though, when you let the scanner s/w do any processing on the data, it will most likely round off or toss some amount of inof which today would still be useful to apps such as PS which have the capability to process high bit depth images.
Regards, Murray
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Old 12-12-2007, 05:38 AM
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Re: Adjust pre or post scan?

Some fascinating information, and with technical specificity that is a delight to see. But it seems to add a third spoke to my query rather than verifying either of the existing two.
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Old 12-12-2007, 08:54 AM
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Re: Adjust pre or post scan?

When I used to scan or have scans done, I always ask/ed for the raw data. Especially with negatives.
The scanner will capture info just like a digital camera which makes it ideal for a lot of things. I still have a couple of clients that shoot film, specifically negatives. I have my scanner set up to capture the negative so that the scan looks exactly like the negative I would hold in my hand. Then I came up with a formula to convert it in photoshop so that it keeps all of the shadow detail and tone etc. So far it has been better than letting a scanner do the adjustments for me.
My guess is that the way it captures and retains the info is similar to what you are looking for. All scanners are capable of doing this, from the high end scanners down to the lowliest. I have done it on a little $50 dollar canon scanner up to $200,000 scanners.
For the low end scanners, the only software that I am aware of that allows you to capture the raw data is Vuescan. The scitex scanners are capable of doing this also with their own software. Hell is a problem because you need to "trick" the instrument into believing it is capturing one way but giving you a different result.
I just got rid of my Powerlook 3000 that used to give me gorgeous scans this way. As a matter of fact I will be adding a couple of shots from it to my website in a week or so.

Chris
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Old 12-12-2007, 10:22 AM
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Re: Adjust pre or post scan?

Hmmm...so now I'm wondering if Mr. Hamrick or the SilverFast freunde might not be on to something after all. In the past I'd chalked them up to workflow convenience and scan automation rather than actually performing tasks Photoshop can't do.
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Old 12-12-2007, 10:30 AM
pixelzombie pixelzombie is offline
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Re: Adjust pre or post scan?

what do you mean by raw data?..i was always under the impression it was best to make adjustments on the scanner as it would use the data while it was in pure digital form, at least on the crosfield scanners and it also made for a quicker turn around...
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Old 12-12-2007, 10:55 AM
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Re: Adjust pre or post scan?

It might make for a quicker turn around, but there is always some sort of clipping going on. For instance, you might not have the tonal range you want in the shadow end, or the highlights have been pushed to far for you to work and are blown out. How does the scanner operator know what is the best setting in the highlight range is for a retouch to be done? By choosing to blow out what should be a 6-4-4 or 5-3-3 instead of, say, a specular, you have just irreparably lost some needed 1/4 tone info.
Some of the higher end scanners do not have the ability to turn off sharpening. They can turn it off in the software, but there is usually hardware sharpening going on that can not be turned off. So much for sharpening for output destination.
I have found that I can get much more shadow detail and range than what the scanner operator chooses.
Also, there is no color imbalance happening when you just capture the raw data.

If you have not yet noticed, the common thing here is the influence of the scanner operator. The operator is one more "tool" that is thrown into the mix that the post production artist needs to correct for if it is used wrong.

So, the raw data has no sharpening, no color cast, not plugged shadows, no lost highlights, and can have no mismeasured/generic color profile attached.

The trick is to be able to convert the negative you have captured correctly, or to process the positive captured properly.

Just like a raw file from a camera.

Chris
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Old 12-12-2007, 01:09 PM
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Re: Adjust pre or post scan?

Chris, you are bang on. The trick is to get all of the raw data picked up by the sensors and A/D converters and get it into PS before any adjustments are applied because clipping will occur. This is the same reason why not to allow a digital camera from applying the user settings and saving the file as a jpg. The only problem is that digital cameras are designed to put out RAW data. I am not sure what you can trust coming out of certain scanners, even with all of the corrections disabled.
Regards, Murray
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Old 12-12-2007, 01:32 PM
Jerryb Jerryb is offline
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Re: Adjust pre or post scan?

hi doug,
now one hand i am bone head novice when it come to photoshop... I am a work in progress...lol...

but scanning I know a little bit about.... What I think the article is talking about is the color depth of the scan... I think all your scanners will 24 bit color depth scanning (ture color) but you have many printers that scan at 32 or 48 bit color depth I think I have seen some scanner even higher! ..... The problem though is there not that many graphic programs that will able to you access those extra bits of depth....!! generally it your high end graphic programs that can like your photoshop, it has the tools to address 48 bit color depth ....

Now one area I don't quite understand... and that is your windows, the monitor and the graphic card .... when you pick 24 bit color you get 24 bit color however... on your graphic card if you pick the 32 bit setting... on most machines that is not 32 bit color!!!! it really 24 bit color.. the other 8 bits are to facilitate increasing the display performance of a image!!! .....

I do not how photoshop compensates on one hand editing a 32 or 48 bit image and yet displaing on a 24 bit graphic card setup without some dithering/clipping being done....

now you wanted some references so i did a little serch to back up .. smiling.. what I am saying....
http://findarticles.com/p/articles/m...5/ai_ziff25240

http://www.bhphotovideo.com/c/produc...tudio_6_0.html

Now this is a epson page... it gets a little technical plus it slanted toward epson... smiling... what interesting... is for normal scanning it does 48 bit but dithers it down to 24 bit...... for it output! but i haven't fully read it to completely understand.. it appears that epson believe that you get better results when scanning at 48 and then let it software dither it down to 24 instead of just straight scanning at 24 bit!
http://files.support.epson.com/pdf/exp16_/exp16_ts.pdf

http://www.scantips.com/chap3d.html

and you'll find this overview of the subject interesting.
http://www.pcmag.com/article2/0,4149,1213576,00.asp

this is a more technical...
http://ccdl.libraries.claremont.edu/...tPractices.pdf

well that my offering I hope that helps you understand........

Quote:
Originally Posted by Doug Nelson View Post
In the Jan/Feb issue of Photo Techniques there's an article by Ctein titled "The Right Way to Scan". In paragraph three he states "All scanners collect extra value levels internally, and they are available to fill in any gaps in the histogram when you expand or compress parts of the tonal range". This is in reference to using levels or curves in the scanning software.

This is news to me.

Does anyone have any manufacturer data on this issue? If I understand what he is saying (and I probably don't), the scanner is either magic or holding back valuable data that we could be using.

Before anyone jumps in to say he's talking about 16bit vs. 8bit, no he's not. But I also know Ctein tends to know what he's writing about, so I'm honestly looking for expansion on this concept.

My own understanding of scans is that they're like raw files in a way, in that you get the raw data during the scan and then any adjustments are made after that point. This is true whether done in the scanning software or in Photoshop. If he's right, I'll need to rethink my scanning workflow.
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  #10  
Old 12-19-2007, 12:51 AM
pixelzombie pixelzombie is offline
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Re: Adjust pre or post scan?

Quote:
Originally Posted by cricket1961 View Post
I have found that I can get much more shadow detail and range than what the scanner operator chooses.

Chris
and how would you go about such a task?
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