Scanner as densitometer.....

[Kirk Gittings]

My densitometer died. I've got enough experience to make do with a "proper proof" but.......Has anyone ever determined an accurate, repeatable method of using a scanner as a densitometer for B&W? I feel like it could be done but haven't figured out a way to create a standard and so never got past the "I wonder" stage.

I suppose you could start with an ICC target? To calibrate your scanner and then use measurements off the grayscale part of the target to check against the densities on your b&w negative? Except of course the target is a positive with relatively short Dynamic Range and the neg is a negative.

Hmmmm. any thoughts?

[Larry Gebhardt]

I had it roughly working with negatives. I scanned a step wedge along with the negative and set the range based on the step wedge. Then I plotted the pixel values in a spread sheet vs the step wedge values. Plotted a graph and used the eye dropper tool and the graph to read the values. It worked, but you needed to make sure you didn't change anything on the scanner. It was also painfully slow since I didn't automate any part of the lookup. It wasn't long after that that I bought a densitometer.

I never tried it for prints, but with a calibrated step wedge it should work as well.

[Kirk Gittings]

Thanks, food for thought.

Another thought related to this-not as precise. Is there something like a "proper proof" workflow for a scanner-doing a raw scan (on a calibrated scanner negative as positive) then just setting the black clip based on film edge-minimum clip required to render film edge as black.......letting the highlights fall where they may?

[Leonard Evens]

Vuescan gives you a reading for what is under the cursor, for bw or color. But the problem is that in a normal scan, the software adapts the readings to the negative, so the readings will be relative rather than absolute. So you have to standardize how you do the scan so that it doesn't do that. I'm afraid I don't remember how to do it, but I did do it some time in the past. The help files for Vuescan may tell you how to do it. Or, if you send email the Ed Hamrick, he will probably tell you. Once you have done that, it would simply be a matter of taking readings from some standard source such as a step wedge for the purpose of calibration.

[Nathan Potter]

Kirk, I frequently do almost exactly as Larry described. Set the scanner conditions exactly the same each time for the step wedge (calibrated Stouffer) and the negative; they need not be scanned at the same time. V750 is very consistent. Read off the density number with the eyedropper in PS (0 to 256) for both the step wedge and negative before doing any corrections. Make a nomograph of step density vs eyedropper value. Check calibration periodically. Quite a sensitive procedure but a PITA to do. You don't have to go to the pixel level though.

Nate Potter, Austin TX.

[Henry Ambrose]

Thanks, food for thought.

Another thought related to this-not as precise. Is there something like a "proper proof" workflow for a scanner-doing a raw scan (on a calibrated scanner negative as positive) then just setting the black clip based on film edge-minimum clip required to render film edge as black.......letting the highlights fall where they may?

Yes, but you can adjust both ends and capture a bit past black and a bit past white to adjust after scan. No point in throwing away before scan.

[Henry Ambrose]

My densitometer died. I've got enough experience to make do with a "proper proof" but.......Has anyone ever determined an accurate, repeatable method of using a scanner as a densitometer for B&W? I feel like it could be done but haven't figured out a way to create a standard and so never got past the "I wonder" stage.

I suppose you could start with an ICC target? To calibrate your scanner and then use measurements off the grayscale part of the target to check against the densities on your b&w negative? Except of course the target is a positive with relatively short Dynamic Range and the neg is a negative.

Hmmmm. any thoughts?

You're headed in the right direction but you should use a B&W negative step wedge as your standard to compare to your negatives. There is no real calibration of a scanner in B&W, but you can use a reference negative for comparison. It'd be pretty simple to lay the reference and the test neg on the glass side by side and scan them together. If not that then save a scanner setting that you use for this purpose every time.

[polyglot]

I would like to do this for BTZS purposes but just haven't bought a step wedge yet. Certainly you can do it in VueScan by using known settings (warmup time on lamp, fixed RGB gain, fixed everything in the colour tab, etc) and then interpreting the 8-bit values that are displayed under the eyedropper. There's a lot of mapping from raw values to 8-bit values though and if you're in negative mode, there is a gamma involved.

However, I suspect a better approach would be to do the fixed-process scan thing (as positive) and save the 16-bit raw scan data as TIF. You can then open the TIF in the editor of your choice and determine the mean value over an area to high precision - the averaging is important because of grain and noise. Of course, you then map that to a density using a reference scan of a step-wedge.

I also suspect that if you can include some raw scan-platen (i.e. with NO film in the optical path), that might get you a reasonable 0D reference point and allow you to directly measure density (to within the linearity of the scanner CCD) without requiring a reference step-wedge for calibrating it. Say the 0D calibration value is M, then at some other region with mean value N, D = log (M/N). Clearly it would be beneficial to verify this at least for each scanner model against a step-wedge before relying on it, but if it works it means you could do density measurements that are immune to fluctuations in the backlight level or variations in the scan exposure time. The primary limitation is that you need a white-point that is not clipped, either numerically or electrically, and that would limit your Dmax unless you also calibrate the linearity of your scanner's response with respect to its exposure time.

[Bill Burk]

In VueScan, under Prefs... Enable density display.

Then in the Preview pane... Hold down the control key.

[Kirk Gittings]

OTOH for a down and dirty estimation of your processes, it is pretty easy on your histogram to just set your black point on the clear film edge, bring in your highlight slider in till it just touches. This will tell you roughly a couple of things real quick (if you remember your shadow highlight exposure for the negative) about your ISO setting and development. This is not tooooo different than the old "proper proof".

[mandoman7]

There's a nice used x-rite on ebay for $100 presently. Probably could get one for less with a little searching. But I've found that the negative densities that we used to like for darkroom printing, developed via the proper proof method or others, aren't the same as the ones my scanner seems to like. The dense neg that used to give the rich tones in print now seems to block the highlights a bit on the scanner. Highlights in general, in the digital arena, seem to be a different animal.

[Kirk Gittings]

http://www.babytrend.com/joggers_single/JG94052.html

True. If you are going to make a negative that will possibly be used on both silver and ink prints you have to be careful on the highlight placement and development-which is why I have gone over to tanning developers.

[Robert Ellis]

This is a fascinating post, and I believe I want to try it. Does anybody have a good recommendation for a step-wedge? I'm not sure exactly which one I should buy. A link would be very helpful!

Thanks,

Robert

[Peter De Smidt]

How about the Stouffer TP4x5-31? See: http://www.stouffer.net/Photo.htm#Transmission%20Projection You can get it calibrated if you prefer.

[Kirk Gittings]

How about the Stouffer TP4x5-31? See: http://www.stouffer.net/Photo.htm#Transmission%20Projection You can get it calibrated if you prefer.

What does that mean you think?

[D. Bryant]

Thanks, food for thought.

Another thought related to this-not as precise. Is there something like a "proper proof" workflow for a scanner-doing a raw scan (on a calibrated scanner negative as positive) then just setting the black clip based on film edge-minimum clip required to render film edge as black.......letting the highlights fall where they may?

Save yourself the hassle and purchase a used XRite 810 for about $200-$250 or less. Scanners are slow and DR limited and the tend not to be linear in the toe and shoulder.

[D. Bryant]

Thanks, food for thought.

Another thought related to this-not as precise. Is there something like a "proper proof" workflow for a scanner-doing a raw scan (on a calibrated scanner negative as positive) then just setting the black clip based on film edge-minimum clip required to render film edge as black.......letting the highlights fall where they may?

Save yourself the hassle and purchase a used XRite 810 for about $200-$250 or less. Scanners are slow and DR limited and the tend not to be linear in the toe and shoulder.

[Bill Burk]

What does that mean you think?

I believe they might read all the densities of all their step wedges on lab-calibrated equipment, and when they have a sample that falls within "tighter" tolerances they print out the readings on the sleeve and call it "calibrated".

What it means to you is that instead of graphing step 3 as the nominal 0.35 you know the X-Axis for that step is really 0.34. You get smoother curves that more accurately reflect reality.

Something like that.

You can do practically the same thing by sending a non-calibrated version to a friend and ask them to write the readings they get. That would probably be close enough to be an improvement. As far as the differences between a calibrated test strip and one calibrated by a friend (to quote my favorite Todd-Zakia line) "The differences that do exist are so small they are not important to us."

[Kirk Gittings]

Save yourself the hassle and purchase a used XRite 810 for about $200-$250 or less. Scanners are slow and DR limited and the tend not to be linear in the toe and shoulder.
Don, Rather than another piece of equipment, I was looking for some method with my 750 that I could do as I was doing my quicky proofing on the scanner.

[D. Bryant]

Don, Rather than another piece of equipment, I was looking for some method with my 750 that I could do as I was doing my quicky proofing on the scanner.

Well this topic has been discussed on certain fora for years, especially in regard to producing digital inkjet negatives for contact printing. A scanner just seems like a natural contender. In the end if you need a densitometer then use a densitometer, it will serve you much better. I know Vuescan will spit out D-log values and perhaps certain versions of SilverFast may. You may be able to edge by with reflection densities but for film densities that's a different horse to ride.

A spectro may be a better all round choice for reflection measurements, though I don't own one so I can't really comment.

[Ed Richards]

Vuescan will also let you lock exposure. You could scan your wedge, record the density values of the steps you care about, lock the exposure, then scan your negative. That should make the density values it displays comparable.

[Kirk Gittings]

That seems like it might work Ed.

[Kirk Gittings]

FWIW, my primary seat of the pants method over the years has been a version Picker's proper proof. The key to is a contact sheet with the minimum exposure necessary to render film edge as black. From there it is easy to get a rough idead about the accuracy of your film ISO settings and highlight development with a particular film dev. combination. It actually works quite well on its own without using a densitometer-not precise but it will do. I only used this method for a couple of decades.

I think I can do something similar by doing a raw preview in Epson 750 software-importing it to PS with no settings and then only setting the black point just high enough in levels to render the film edge as black (K value in the Info panel at 100% output). From there you can get a pretty good idea about your ISO settings and development for the highlights. This gives you some rough information quickly in the flow of things about ISO settings, shadow placement, highlight development/placement, filter factors etc. I think the step wedge idea might tighten this method up.

[Bill Burk]

FWIW, my primary seat of the pants method over the years has been a version Picker's proper proof. The key to is a contact sheet with the minimum exposure necessary to render film edge as black. From there it is easy to get a rough idead about the accuracy of your film ISO settings and highlight development with a particular film dev. combination. It actually works quite well on its own without using a densitometer-not precise but it will do. I only used this method for a couple of decades.

I think I can do something similar by doing a raw preview in Epson 750 software-importing it to PS with no settings and then only setting the black point just high enough in levels to render the film edge as black (K value in the Info panel at 100% output). From there you can get a pretty good idea about your ISO settings and development for the highlights. This gives you some rough information quickly in the flow of things about ISO settings, shadow placement, highlight development/placement, filter factors etc. I think the step wedge idea might tighten this method up.

Can you simply "tape" the step wedge onto the glass next to the negatives. The half-inch 21-step can usually fit for the purpose. Include the image of the step wedge on every scan. No matter what your scanner settings are (you can find mistakes this way). You will always be able to eyedropper the negative's highlight and find the matching step wedge "step" - to know the density range. Or find any density of any spot on the neg this way.

[bob carnie]

If you are using a Mac and like the L channel then use a colour meter to read all your values. I use a colour meter with my scanner to fine tune density and colour adjustments that the scanner software seems lacking in. This meter is independent to PS and your scanner software and is wonderful to work with.

On all our computers a Digital Colour meter is set up to CieLab settings with a small apeture so you can get in and get about a three to four reading.
I find it invaluable. I like Bills idea of including a step wedge for comparison.


Can you simply "tape" the step wedge onto the glass next to the negatives. The half-inch 21-step can usually fit for the purpose. Include the image of the step wedge on every scan. No matter what your scanner settings are (you can find mistakes this way). You will always be able to eyedropper the negative's highlight and find the matching step wedge "step" - to know the density range. Or find any density of any spot on the neg this way.

[Kirk Gittings]

Can you simply "tape" the step wedge onto the glass next to the negatives. The half-inch 21-step can usually fit for the purpose. Include the image of the step wedge on every scan. No matter what your scanner settings are (you can find mistakes this way). You will always be able to eyedropper the negative's highlight and find the matching step wedge "step" - to know the density range. Or find any density of any spot on the neg this way.
That should work IMO.

[Tin Can]

Old thread.

Is there any newer thinking on this scenario?

[Andy Eads]

In the appendix of my book posted here: http://www.largeformatphotography.info/articles/VIDEC.pdf
is a means of using a spot meter as a densitometer. I've had pretty good results with this method though it is tedious. Scanning has the advantage of highly localized measurement. In a pinch however...

[swmcl]

Hi,

Can I offer my test results for discussion ? I personally don't see how others cant use these results with a fair amount of accuracy.

Cheers,

Steve

135151

[Tin Can]

Hi,

Can I offer my test results for discussion ? I personally don't see how others cant use these results with a fair amount of accuracy.

Cheers,

Steve

135151

Thanks! That is handy and useful.

As a hobbyist, I am not concerned with absolute scientific and traceable results but more a personal working index and method, not unlike finding personal EI or chemistry preferences.

Perhaps others have different results?

[swmcl]

Sorry I should have mentioned that it was an Epson v700 scanner and I use Vuescan.

To me it says that the film density should be between step 3 and step 21 which would be 7 optical density doublings on film. Optical densities lower than say 0.25 or 0.3 should be avoided and also optical densities above 2.0 which are at the top end of the scanner ability with it reading 239 out of a possible 255 in 8-bit mode (roughly).

As I understand it, a negative properly developed for printing will seek to put the shadows fairly close to the knee of the curve (ie. try to have discernible but low density) and the highlights such that they fit for a specific paper and condenser (ie. say 1.2 above the shadow). As I also understand it. this practice is not necessary for scanning in that the optical density of the negative probably should try to take up as much of the scanners ability. In this case, a negative for the scanner should seek to reach from say 0.25 (or 0.3) through 2.0 and still have room to play on either side. This would lead to a massively more dense negative in nearly every case.

It seems to me that this is opposing the commonly accepted lore whereby people are developing very flat negatives for the scanner. I am yet to fully play with this as yet. Whatever the outcome, it would be a very safe bet that you cant go wrong with strong exposure and strong development. You will get a result from the scanner but it wont be optically printable.

I am always happy to help.

Cheers.