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Camera "Scanning" -- Use Di-Chro Head to undo Color Mask?
Old 06-12-2017   #1
ColSebastianMoran
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Camera "Scanning" -- Use Di-Chro Head to undo Color Mask?

Looking for feedback:

Camera scanning of color negatives. If you use white light, the digital camera image of the negative is very orange, the red channel clips first, and the Gr/Bl channels have condensed histograms. The opposite of ETTR.

So, I started thinking, can I remove the orange mask by using my Di-Chro head to fully offset the orange mask?

Would like feedback on the idea. Does this make sense? Drawbacks? Pitfalls to avoid?

I'll add details below, but that's the essential question: Digital camera scan, Di-Chro head to add the opposite color so the orange mask disappears?
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Old 06-12-2017   #2
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In another thread, Huss offered this tutorial for Camera-Scanning of color neg material.

http://www.mfphotography.ca/michael-...digital-camera

He's using a light pad, daylight balanced white light.
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Old 06-12-2017   #3
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I set the Di-Cho filters on my Beseler Dual-Mode Duplication for +50 Cyan and +15 Magenta, and I expose with flash, not the incandescent bulb.

This gives me a camera capture in which the orange mask is about neutralized and my histograms are all broad, the WB comes from an area of unexposed film. Notice my WB is 4350K and there is little tint.

Next, I set the blacks and white in my RAW conversion (Lightroom) to expand the histogram both ways staying well clear from any clipping.

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Old 06-12-2017   #4
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Next, I move to Photoshop, apply the Color Neg action from Huss's reference (above).

This gives a pretty good color image.

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Old 06-12-2017   #5
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The image above is not quite right, but with a little Lightroom tweaking, I have an image that's better than the mini-lab print from 2010. Quite a bit better.

The negative is from a test of a then-new-to-me Yashica GX on Fuji 200 film in 2010.

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Old 06-12-2017   #6
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So, anyone have any thoughts on using Cyan/Magenta light from a Di-Chro head to offset the orange mask?
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Old 06-12-2017   #7
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Old 06-12-2017   #8
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Yes, it looks good, thank you for the report as I was curious about this. I had read that the dichro heads weren't strong enough filtered to counteract the orange mask, but the flash seems to have done it. Good news!
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Old 06-12-2017   #9
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H, I might have to go scrounge the right parts for a set up like this, for that future moment where my old little Imacon kicks the bucket...
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Old 06-12-2017   #10
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Can't be done literally - it is a mask, not a constant stain, so applying a complimentary constant will not make it vanish. What you can however do is to apply the complimentary colour at the average density of the mask to shift the white point to a more manageable value. But you will still have to undo the actual mask (which presumably is what the mentioned action does).
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Old 06-13-2017   #11
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How on earth then did they do optical C-41 prints back then?
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Old 06-13-2017   #12
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Quote:
Originally Posted by brbo View Post
How on earth then did they do optical C-41 prints back then?
And mini-labs?

I think the mini-lab manufacturers did calibrations for each of the film types. There was enough revenue and they had the resources.

I don't know. How did anyone ever make a C-41 print with good (accurate? believable?) color in a darkroom setting.
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Old 06-13-2017   #13
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Quote:
Originally Posted by sevo View Post
Can't be done literally - it is a mask, not a constant stain, so applying a complimentary constant will not make it vanish. What you can however do is to apply the complimentary colour at the average density of the mask to shift the white point to a more manageable value. But you will still have to undo the actual mask (which presumably is what the mentioned action does).
@sevo, thanks for this thought. Not sure what to make of it.

Yes, the complimentary cyan/magenta shifts the white point to around 4400K, and just a tiny bit of tint, with flash illumination. That's certainly manageable.

The mentioned action? No, it's not doing anything sophisticated. Here is the heart of the action, auto, find dark and light colors, snap neutral midtones. See the resulting curves adjustment below. I'm amazed that this gives the reasonably good auto result, the first positive image above.

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Old 06-13-2017   #14
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Quote:
Originally Posted by ColSebastianMoran View Post
Bigger question is how did anyone ever make a C-41 print with good (accurate? believable?) color in a darkroom setting.
Well, I believe that they did it just like you did (for scanning). If "canceling out" orange mask still left some complex colour mask there would be VERY VERY few optical prints made at all.

But since I've never done an optical colour print, I'll wait for sevo's explanation...
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Old 06-13-2017   #15
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Doing a little research on sego's tip finds this interesting article.

Yes, it's a mask. Yes, the intensity of the orange at any point depends on the exposure of the magenta and cyan layers at that point. Here's a reference with a clean technical explanation.

http://www.brianpritchard.com/why_co..._is_orange.htm

Quoting from the article, "the amount of mask will be inversely proportional to the amount of dye formed. That is, if no dye is present then maximum mask is present and in the areas of maximum dye formation there will be no mask."

Wow. Sounds troublesome. So rebalanced light works on average but not exactly for other negative densities. How big is the difference? Other routes to address it in a camera-scan file from an RGB sensor? I'm rebalancing based on the unexposed area, the densest mask. Should I rebalance on a midtown grey instead? Mind boggles.

Will not anyone rid me of this meddlesome orange mask!

Or, more seriously, won't anyone create software for properly processing camera-scan files from color negative material?

My conclusions so far:
- These brute force approaches are approximations at best
- Keep the camera-scan RAW file and probably the negatives for important color-neg images
- For less serious hots, a camera-scan gives an image that's pretty good and better than the old mini-lab prints. For these snapshots, keep the JPEG and discard the prints, negatives, and RAW files.
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Old 06-13-2017   #16
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The mask is the challenge. There is a photoshop action that does calculations somewhere in the moving picture hinterlands of the internet that I mean to adapt one day. Hopefullly it can be used with some sensible filtration to maximize the data recorded in each channel too.
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Old 06-13-2017   #17
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And, here is someone who purports to have a rigorous technical solution to removing the varying mask. It's re-posting in 2000 from an earlier article at Adobe Forums by Burton.

I haven't tried this and might not.

https://www.dpreview.com/forums/post/499854
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Old 06-13-2017   #18
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I've not captured any color neg for quite a long time. But...

I use DNG Profile Editor to create customized camera calibration profiles for use in copy scanning both B&W and color negatives. For a color negative, I find the most effect way to remove the orange crossover mask is to use a negative image which has a reasonable amount of unexposed, processed rebate to set up the right profile constants. The crossover mask is consistent through the negative film so images processed with the custom CCP invert to a proper RGB positive which reflects the actual color temperature of the light captured.

Someone asked if anyone had ever produced 'accurate' color prints from negatives. Of course we did: we used reference negatives and a densitometer to calibrate the C41 processing machines. This process also establishes the correct filter pack settings for the enlarger and printing machines; it guarantees color accuracy when done correctly. I'm kind of shocked that film aficionados on this forum would not understand that part of the professional darkroom workflow.

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Old 06-13-2017   #19
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Quote:
Originally Posted by Godfrey View Post
Someone asked if anyone had ever produced 'accurate' color prints from negatives. Of course we did: we used reference negatives and a densitometer to calibrate the C41 processing machines. This process also establishes the correct filter pack settings for the enlarger and printing machines; it guarantees color accuracy when done correctly. I'm kind of shocked that film aficionados on this forum would not understand that part of the professional darkroom workflow.
And yet you haven't even touched on the question how that workflow (totally) eliminates colour mask. Do you know the answer?
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Old 06-13-2017   #20
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Quote:
Originally Posted by Godfrey View Post
I use DNG Profile Editor to create customized camera calibration profiles for use in copy scanning both B&W and color negatives. For a color negative, I find the most effect way to remove the orange crossover mask is to use a negative image which has a reasonable amount of unexposed, processed rebate to set up the right profile constants. The crossover mask is consistent through the negative film so images processed with the custom CCP invert to a proper RGB positive which reflects the actual color temperature of the light captured.
Godfrey, I understand you sample the unexposed area of film. What do you do with that sample other than set White Balance? And, is your CPP applied to the negative image, before inverting? Or to the positive after inverting?

Quote:
Originally Posted by Godfrey View Post
Someone asked if anyone had ever produced 'accurate' color prints from negatives. ... snip ...
My question was never whether. All of us have seen great color prints. More like amazement at how great prints were made optically in wet darkroom, given the complexity of the orange mask.
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Old 06-13-2017   #21
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Quote:
Originally Posted by brbo View Post
And yet you haven't even touched on the question how that workflow (totally) eliminates colour mask. Do you know the answer?
It's obvious.

The color mask in negative films was implemented to eliminate channel crossover problems in the chemical reversal color printing process. Without it, you couldn't get a clean RGB positive image from a color negative consistently. The color pack removed it when you made the print. It's a matter of the chemistry involved.

This is completely different from the notion of removing the crossover mask when working with CMY negative with mask -> RGB digitally. Digital negative to positive doesn't need the crossover mask, it's just a bias offset in the CMY channels in the digital space.. So I just filter it out with the customized camera calibration profile. Done.

(Likewise, you can print a negative image for chemical color printing on standard photofinishing equipment by doing a simple color inversion of a positive image and injecting an appropriate mask color overlay onto it. I used to create large format negatives like this, once upon a time, before decent inkjet printers became available in the 1990s...)

As illustration:

I grabbed a little strip of half-frame negatives I saw lying about in my drawer and snapped a photo of it using the Leica SL fitted with a Spiratone Vario-Dupliscope II. I let the sun fall on the diffuser glass to get a simple daylight color balance to the capture illumination. The DNG files were moved into Lightroom.



I exported a DNG compatible with DNG Profile Editor (it was last updated in 2012 so it can't normally open Leica SL DNGs for editing) and opened the editor, loaded a frame. First I inverted the tone curve. Then I sampled the rebate between the frames and adjusted it to come close to neutral bright white (black in the inverted image). Then I exported the edited CCP and restarted Lightroom.

After Lightroom restarted, I clicked on the Camera Calibration panel and chose my newly created "SL-colorneg-reversal" profile. Obviously, the total color matrix cannot be corrected with a single adjustment, but the resulting reversal was pretty close. A couple of minutes tweaking settings in the HSL panel netted this result:



Close enough. I'd export this as a color positive 16-bit TIFF and do my finish rendering on that (it's easier because the sense of the adjustment controls won't be inverted and they'll have more range of operation).

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Old 06-13-2017   #22
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Quote:
Originally Posted by ColSebastianMoran View Post
Next, I move to Photoshop, apply the Color Neg action from Huss's reference (above).

This gives a pretty good color image.

You can correct any color cast left over at this point by converting the image in to LAB color space and doing the corrections there. I have had really good success this way
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Old 06-13-2017   #23
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Quote:
Originally Posted by Godfrey View Post
It's obvious.

... The color pack removed it when you made the print. It's a matter of the chemistry involved.
Chemistry removes the color mask?
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Old 06-13-2017   #24
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Quote:
Originally Posted by brbo View Post
Chemistry removes the color mask?
Light and the filter pack working with the chemistry. Yes. It was formulated to do that.

G
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Old 06-13-2017   #25
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Quote:
Originally Posted by Godfrey View Post
Light and the filter pack working with the chemistry. Yes. It was formulated to do that.
Is it possible to print optically and from scans (with laser light source) on the same paper?
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Old 06-13-2017   #26
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Quote:
Originally Posted by brbo View Post
Is it possible to print optically and from scans (with laser light source) on the same paper?
I not sure what you're asking here, or why a laser light source is being specified for scans...?...for both?

Do you mean, "If I scan a negative can I print it to photosensitive paper and process it in the traditional chemistry the same way I would expose photosensitive paper with a negative and process it?" The answer to that is certainly "Yes" presuming that you have a scan of a color negative that, when printed to the paper, is printed such that the same color light strikes the paper that the optical printing of the negatives do. Such a printing process will likely have its own calibration curves and filter pack requirements because it's probably a little too fussy a prospect to match the printing light from the scan perfectly with the output of an enlarger to paper.

As I said before, I at one time made large format color negatives for traditional printing machines. Given the differences in materials, although they looked pretty much the same to the naked eye, the spectral absorbtion characteristics of the ink on film or paper was a bit different from original negatives (dyes on clear polyester film base) and needed a customized filter pack to print accurately.

If you want to play with the concept, use a digital camera to capture a negative and print it to a 5x7 inch transparency. Then contact print it to color printing paper, obviously using a color pack or filtered light with a dichroic head, and process that. You can come up with some fun imagery that way...

G
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Old 06-13-2017   #27
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Quote:
Originally Posted by brbo View Post
Is it possible to print optically and from scans (with laser light source) on the same paper?
it is, but the paper usually is optimized for one process. An example, this Fuji paper is optimized for laser light printing:

http://www.fujifilmusa.com/products/..._CN/index.html

This one is for both film or digital:


http://www.fujifilmusa.com/products/..._II/index.html
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Old 06-13-2017   #28
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Quote:
Originally Posted by Godfrey View Post
I not sure what you're asking here
Can I optically print a negative on the same paper that minilab laser printers print on (from scans)?
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Old 06-13-2017   #29
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Quote:
Originally Posted by Huss View Post
Quote:
Originally Posted by brbo View Post
Is it possible to print optically and from scans (with laser light source) on the same paper?
it is
How on earth can they do that?
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Old 06-13-2017   #30
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Quote:
Originally Posted by brbo View Post
Can I optically print a negative on the same paper that minilab laser printers print on (from scans)?
Quote:
Originally Posted by brbo View Post
How on earth can they do that?
It's not something that is ordinarily done so the mechanism to do it would have to be contrived. But in the end, it's just paper that you expose to light and allow a negative to cast a shadow on.

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Old 06-13-2017   #31
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Quote:
Originally Posted by Godfrey View Post
It's not something that is ordinarily done...
Actually, it is. People optically print on the same paper that laser printers in minilabs can also use when they print from scans.
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Old 06-13-2017   #32
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Quote:
Originally Posted by brbo View Post
Actually, it is. People optically print on the same paper that laser printers in minilabs can also use when they print from scans.
So if you think you already know all about this, why are you asking these inane questions?

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Old 06-13-2017   #33
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Quote:
Originally Posted by Godfrey View Post
As illustration:

I grabbed a little strip of half-frame negatives I saw lying about in my drawer and snapped a photo of it using ... snip ...
Godfrey, thanks for the illustration and explanation. I agree, this gives color that's close enough. Nice motorcycles, nice color.

I took the jpg of your negative to look at the histogram, the red channel is well to the R of the others. Red will clip first when shooting a color negative in a camera-scan.

My aim with the cyan/magenta light is to bring all three channels up into the same range on the histogram. So that the inverted, color corrected histogram will have fewer gaps. Any thoughts on this idea?
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Old 06-13-2017   #34
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I've been experimenting with different ways of doing the color correction from the inverted color negative:
- eye dropper to set WB
- curves adjustment, auto
- curves adjustment, auto, "Find Dark and Light Colors," and "Snap Neutral Midtones."

The last comes from Option while clicking the Auto button. This unknown-to-me Photoshop option I just discovered in the Action set Huss recommended.

Punch Line: This last does a good job. Damn good job. Here are the options I got from Huss's recommended article:



This auto-option is much better than the first and second, and much better than my past experience trying to get reasonable color.

Godfrey, this auto-option gives a result pretty close to your adjusted image, so it must be doing about the same thing as your profile.

This auto-option may be a silver bullet for getting reasonable color from camera-scans of color negs. Stay tuned. I'll do more with this.
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Old 06-13-2017   #35
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This variable mask thing doesn't seem to be making much difference. If I'm thinking about it right, it would result in orange highlights, or blue midtones in the positive image. Does the mask vary consistently with density? It would be good to see some skin tones, though. I don't have any Adobe products installed or I'd do it, so just to mention...
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Old 06-13-2017   #36
ColSebastianMoran
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Quote:
Originally Posted by Ranchu View Post
This variable mask thing doesn't seem to be making much difference. It would be good to see some skin tones, though.
Yeah, bright colors may be easier than skin tones. I'll see what I have in negatives to try.
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Old 06-13-2017   #37
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You boys are getting too high fallutin' for me.
I just create a profile in LR (too cheap to buy PhotoShop), export to NikFx where I use the correct color cast option. You can save that as a preset in NikFx. Works great for skin tones.



p.s. if I had photoshop I would definitely try the above suggestions.
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Old 06-13-2017   #38
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So. If the channels (histograms) are matched closely by tuning the light source, the (consistent) variable mask just becomes a minor color cast removable in software?
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Old 06-13-2017   #39
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Originally Posted by brbo View Post
Actually, it is. People optically print on the same paper that laser printers in minilabs can also use when they print from scans.
I think 'we' are making it out to be more complicated than it is. The colour head in the printer corrects for the orange cast on the film, whether it is a minilab printer or a home enlarger (for colour negative film).
The photo sensitive paper used is still silver halide based and works with any light source that it is exposed to. It is just that now some papers have been optimized to work better with whatever light source is being used, but they can still be used with either.
Hence the paper options that Fuji shows on its website.

There isn't a special chemical process that removes the orange etc as otherwise we would not have prints that intentionally have orange in them!

The interesting thing to me is the reasoning behind why C41 films have the orange base to them. You can also see this on B&W C41 films like BW400CN, Ilford XP2 etc
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Old 06-13-2017   #40
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So. If the channels (histograms) are matched closely by tuning the light source, the (consistent) variable mask just becomes a minor color cast removable in software?
Yes Sir!

dot dot dot 10 characters.
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