Challanging assumptions about scanning B&W

[Jeffrey Sipress]

Very interesting. I'm scanning a lot of B&W lately on my 4870, both from negs and from NPS color negs that I will convert in PS. I'm sure we have all noticed that some images just seem to scan better than others, with others often engaging in a fighting match with you. Say you've got a wonderfully captured B&W neg that contains a good eight to ten stop range of tonalities. How much of that will be noticeably transferred to your digital file at scan time? Sadly, not much. Nobody ever relates the scale of the film to the scale of the device. Hell, no one really knows the scale of their scanners because manufacturers don't divulge that information, and feed us some other unit of measure called dmax. What exactly is that? How does it relate to stops? When a nice soft scene (on a color tranny, color neg, or B&W neg) that's easy to expose and typically has a three to five stop range comes along, it will scan beautifully, and be truer to the original. That's because the scale of the device is more closely matched to what the film is giving it. I scanned the Kodak Q-14 greyscale test strip, which goes from 0 to 100% black in 20 increments, and measured the values of each area in PS and output them to excel to create a graph of the curve for the resulting scan. It was dismal! This is all why I think Kirk is on to something using color neg film for B&W work. The scale of that film better matches the scale of the scanning device. Sometimes scanning a color transparency for conversion to B&W is better than anything else. It simply matches the limitations of the system. No fighting!

[Kirk Gittings]

Henry,
Sorry I don't have any up in Chicago now. I will next summer at the Schneider Gallery, but i don't know the dates.

I wish i had time to do the side by side tests that you require. I don't right now. My workflow for FP4 negs. is this with the 4990 (or Imacon when I am in Chicago). Adjust overall tonailties so that they are in the ballpark for final print with plenty of shadow and highlight detail. Scan at 720 DPI RGB (Imacon gives a better scan in Grayscale) at largest size I will ever print (20x24). Discard all but the blue channel (least noise and sharpest). Spot the file at 100% and do some capture sharpening. Down size to 360 DPI. Tweak levels and curves in adjustment layers. Do burning and dodging via Snapshots and history brush. Do test print. Adjust levels and curves again via layers. test print. Final sharpening via Optipix Safe Sharpen 1X in a duplicate layer. Final output downsizing (usually to 11x14 or 16x20) done by Imageprint RIP. Final Print.

[Henry Ambrose]

Jeffery,
What we're talking about here is not new, its been beat about for years now on other forums and by other individuals. Lots of folks shooting 35mm use color neg and cheap commercial processing to do their "B&W" work. The density range of the color negative film will fit the range of most any desktop scanner so it works great for digital B&W printing. And I'm referring to inexact exposures and wide ranges of scenes on one roll. But you can fit your "real" B&W film to your scanner so you don't have to retool your process completely. After all, you do have the luxury of adjusting exposure and development on each individual sheet. But still, what makes the best picture makes the best picture.

Where we really get lost is in not knowing what the scanner is doing even when we think that we've "turned off the software". As far as I can tell they behave differently across brands and I think this accounts for some of the differences we are discussing here.

Ed, next time you scan a negative and bring it into PS at 16 bit, look at the histogram to see if you got it all wadded up instead covering nearly the entire available range. This does make a difference when you start adjusting the file -- or it might be just the interpretation you wanted. The problem is that the second scenario occurred by accident.
; >)

Kirk,
Your workflow is not all that different from mine. I do think its funny that you use the blue channel, Ed uses the green channel and I use all three!

[Paddy Quinn]

Jeffrey

It sounds more like problems with limitiations in either the scanner you are using, the software or operator skills.

I have few problems capturing the full range of a B&W negative via scanning (and scanning my Stouffer 21 step transmissive wedge gives a full range of steps with nice seperation).

Scans usually show a greater range of detail from shadow to highlight than I ever got in a darkroom print (and of course translating the scan and file into a "digital" print presents a similar challenge). Scanning to give your 8-10 stop range isn't impossible at all .

"Hell, no one really knows the scale of their scanners because manufacturers don't divulge that information, and feed us some other unit of measure called dmax. "

It is D(ensity)Max - and goes with D(ensity)Min to give you the Density Range of the scanner. however accurate or not the manufacturers measuring of it may be for a particualr scanner so the general principle is the density range of a negative (hypothetical numbers) might be say 2.9 while that of a transparency is 3.6 - the difference due to the offset caused by the different types of film base (clear v's cloudy).

Most decent flatbed transparency scanners can do a pretty good job of capturing the full range of a negative (colour or B&W) - they can be challenged by the higher density range of transparency film

The problems comes with how you capture that information - i.e. how good the software is and how good the operator is at using it and then how well that data is dealt with in Photoshop or whatever the imaging programme used. Much scanner software does a rather bad job at dealing with both types of negative film, clipping lots of the information and having problems inverting the image correctly. Most also go about dealing with the orange mask incorrectly. In addition, Photoshop's "Invert" command also doesn't go about inverting the image the way you would think it does and this itself introduces all sorts of problems

It sounds like you have probably put a lot of time and effort - perhaps many years - into developing your zone system skills. Digital skills have an equally steep learning curve and take at least as long to develop to a level of expertise.

[Kirk Gittings]

"Kirk, Your workflow is not all that different from mine. I do think its funny that you use the blue channel, Ed uses the green channel and I use all three!"

Henry, I think it really varies by the scanner and that is why everyone has to test this for themselves.

On my 4990 the Blue channel is clearly sharper and less noisy than the others. If I remember correctly my Canon 950f (I returned three of them for streaking and finally gave up) had less noise in the green but was sharper in the blue. The Imacons I have tested are very very sharp in all modes but have allot of noise in RGB. So I can get the best b&w scan from the Imacons in the grayscale mode. I have only tested Vuescan on Epson scanners. The only way it surpased Silverfast was in the singlepass multisampling which gives a sharper result than the SF multipass sampling. The SF eliminated noise better but the many passes resulted in a less sharp image than the Vuescan.

No one should be loyal to their equipment because they spent allot of money for it. The Imacon I use cost $16,000.00 but is only better than my $500.00 4990 in terms of sharpness and that only minutely shows up in a 16x20 or larger!TEST!

[Jeffrey Sipress]

Thanks, Henry and Paddy. Perhaps my wedge test was useless, since it was a reflective scan,and doesn't prove what a transmissive test would yield. I need to get hold of that Stouffer strip. I've never heard or it.

My images are coming out better than the test I did should allow! I hope you're right about my scanner capturing all of what's on a B&W neg. I'd just like confirmation.

[Ed Richards]

> Ed, next time you scan a negative and bring it into PS at 16 bit, look at the histogram to see if you got it all wadded up instead covering nearly the entire available range.

Of course it is all "bunched up" - the point I am making is that "unbunching it" is a computer calculation that is about the same as applying the levels command with gamma adjust in photoshop or PWP. The advantage of doing it in the editor is doing it once saves rounding errors over doing it twice. There seems to be a notion that what is going on in the scanner computer is different from what is happening in the computer on your desk. Once you have the CCD data into digital form out of the sensor, it does not matter where you scale it, except that you get more control by doing it all in the editor. This is esp. true if you are doing the scan once approach - what I save as the master file has no scaling applied at all, so I am not locked into white and black point and gamma choices made when I originally scanned the negative. This is useful because black and white points and gamma interact with curves - it is very useful to have both on layers you can play them off against each other.

As for the invert command - at least on B&W I do not see it doing anything unusual. The histogram seems to a mirror of the histogram before inverting, i.e., it is flipped about the midpoint, with data being bunched at high end rather than the low end. What are you seeing that is unusual? I may be missing it. I usually invert in PWP anyway - it is much faster than Photoshop for resizing and inverting

[Frank Petronio]

Just a vote for VueScan with basic tonal editing done in the preview and very little else. It works with all of my scanners and is pretty nice software.

[Paul Butzi]

The advantage of doing it in the editor is doing it once saves rounding errors over doing it twice. There seems to be a notion that what is going on in the scanner computer is different from what is happening in the computer on your desk. Once you have the CCD data into digital form out of the sensor, it does not matter where you scale it, except that you get more control by doing it all in the editor. This is esp. true if you are doing the scan once approach - what I save as the master file has no scaling applied at all, so I am not locked into white and black point and gamma choices made when I originally scanned the negative. This is useful because black and white points and gamma interact with curves - it is very useful to have both on layers you can play them off against each other

I'd agree that, in the abstract, it's better to perform all the scaling and curve adjustments exactly once, if all other things are equal. I even agree that it's quantization/rounding errors that increase if you repeatedly perform the calculations.

That said, I would disagree with the idea that this is significant.

First, the calculations done in the scanner/scanner driver may well have more data to work with than the calculations done in photoshop. That is, the scanner may well have, say, 18 bits per channel to work with - those 18 bits are then run through the scanner scaling and curve calculation, with the results being expressed in properly rounded 16 bit values. You're also assuming that the scanner cannot adjust exposure and amplifier gain based on the setting of white point and black point. While that might be true for some very cheap scanners, I know it's not true for at least two of the scanners I've owned - an Epson 1640SU and a Microtek 1800f, because both of those scanners scan more slowly when scanning negatives when the white and black points are set up higher (to scan negatives with high base density).

Only if ALL the data that was available on the scanner side was present in the 'raw' scanner format would Photoshop have all the data. I don't know, but I expect that the 'raw' scanner output is not this wider data format, but instead just the same scanner software calculation run with the black point and white point set to the extremes, and with the tonal distribution being set to some default curve. So, in the end, the calculations get done twice, no matter what you do.

Also, we're talking about truncation/rounding introducing noise in the image. That means that, for any given pixel, the maximum error introduced by such rounding will be a single bit error in the least significant bit - a relatively small error.

And, if it's true that the scanner can adjust exposure and gain based on the settings of white and black point, AND the scanner works internally with a wider data stream than is passed to Photoshop, then you'd definitely be better off (in the theoretic sense) setting the white and black points carefully in the scanner software (thus increasing the number of bits available to express the data, and getting more resolution passed to photoshop) and taking the minor single bit hit when you do further adjustment in photoshop.

All that said, I have a hard time believing that it's possible to discern the differences if you have a workflow which is not narrower than 16 bits between the scanner and Photoshop.

[Kirk Gittings]

"The bottom crop is a shadow performance test suggested by Paul Schilliger. It examines how much detail the scanner is able to pull out of deep shadow, and how much noise is in there. To see what was happening in the shadows, I used Photoshop to apply the steep curve that you see on the right." From this sites scanner comparison.

Check out the bottom image in the scanner comparison and compare the Creo, Imacon Prec. II, and the Epson 4990. These all have a steep curve applied in PS as I noted above that I apply to my cloudy skies. Notice the increased noise in all but the drum scan.

My experience suggests that if this curve was applied in Silverfast (or whatever software) originally in the scan, when the sampling is done, that this noise would is greatly reduced, because this increased noise is a result of expansion or clumping (or something) of the pixels in the transition areas between tones. Therefore...... similar to what Paul stated above, it is better to do this tonal expansion as much as possible in the original scan to minimize this granularity.

I have struggled with this problem for over a year on everything but drum scans and the solution that seems to work is to do as much of the tonal manipulation in the original scan as possible.

If my thinking is wrong here I would like to hear why? How is my experience inconsistent with the scanner comparison's examples?