No, you are correct Adrian. You measure the densities of the mask to R/G/B and then set R=0. Once that is done, the G and B numbers become the needed offset.
The next thing we do in design is to add about 50R + a fudge factor for the average darkroom enlarging lamp and to give us some leeway to avoid any Cyan filtration.
If you do a raw sensitometric exposure of color paper to white daylight or tungsten you get a red step wedge that goes to black at Dmax.
PE
There seems to be a fair amount of concern over using a bayer array and it causing problems with scanning film. As a user of a bayer array based scanning system, it's much less of an issue than what people probably think it is. A modern APS-C based camera has been at the 24MP mark for quite some time. At 240 pixels per inch print resolution, it will make a very nice looking 16x24 inch print of 35mm or 16x20 print of a 6x7 120 frame. Modern Bayer interpolation algorithms are very, very good. While 16x20 is not a large print by large print standards, it most definitely is not a small print, and based on the number of requests I get to make prints, is absolutely on the large end of what is generally printed. 5x7 followed very closely by 8x10 and 11x14 by a distant third is what I get most requested to print. Every once in a while I'll get a request to do something larger, but I easily print hundreds of the other sizes for every 11x14, and dozens of 11x14s for every larger request.
Don't get me wrong, I'm generally all for more resolution, but there seems to be a bit of a disconnect between how much resolution people want to scan at and how much resolution you actually need for common stuff. If you're worried about the bayer array causing weird aliasing artifacts with the film grain, you maybe might have to worry about that if the particular camera you're using doesn't have a low pass filter (like some Nikon models), but for pretty much everything else, there's a low pass filter that does a very good job mitigating problems without completely destroying fine detail. The camera manufacturers are not dummies when it comes to this sort of thing. Combine that with the somewhat random nature of the grains/dye clouds and the modern AHD Bayer interpolation and the whole "artifacts from the bayer array" thing hasn't really been much of an issue in my experience. Of course I get the occasional comment from a customer about how big the grain of some emulsion is when somebody takes one of my DNGs and looks at it at 1:1 or 2:1 in the LR develop module. I inevitably have to gently remind them that when they do that, they are effectively blowing it up to a giant print (by giant print standards) and looking at that with a magnifying glass, and that maybe a more realistic way to look at it is to put it full screen on their big 60-70 inch 4K TV and see what that looks like instead. Almost always, once they do that they comment that it looks a lot better that way and is pretty sharp. And that's with a 35mm frame size. A 4K TV is ~8MP and looks really good, even at the large end of the TV scale.
The point is, more resolution is generally better, but in reality, for most display purposes, you actually need a lot less than you think you do, and 24MP covers a really large swath of that. If you want to scan 120 and 4x5 with a 50MP Canon 5Ds, you can and it will look better than a 24MP scan at really large print sizes, but again, now we're getting into truly ginormous prints. Just some food for thought.
The effect demosaicing has on edges and fine, high contrast detail is basically close to what a sharpening algorithm does. You can of course roll the effect back, but that will just result in more guesswork.
Sensor shift and individual RGB sensors of course introduce a whole set of new problems
True. You'll still want to sharpen your file somewhat, just as you'd control various other parameters on RA4 in the darkroom though.Film rolls contrast off as you record finer detail, which has quite a bit of clamping effect on the awful things you’d otherwise see if you originally shot the image directly into the bayer sensor instead of shooting it on film and “scanning” it with a bayer sensor.
A lot of the common visual artifacts introduced with a bayer array and related interpolation aren’t necessarily a 1:1 when scanning film with a bayer array. I’m not saying it doesn’t happen, it’s just not as unpleasant.
True. You'll still want to sharpen your file somewhat, just as you'd control various other parameters on RA4 in the darkroom though.
Bayer artifacting could theoretically get in the way of that.
"People", not you I know, often forget that a negative is the raw data, not the finished product. Often you hear naive "purists" proudly declare how little "manipulation" they've done to the inverted negative.
I’m interpreting “speed offset in the layers” as a global multiplier if done digitally, as the net result is the orange cast is effectively dialed out as a result of the multiplication that is effectively happening as a result of the layer speed differences.
If that is the case, then doing a raw global multiplier on each channel to dial the mask out isn’t totally wrong, as that produces the same effect as having each layer a different speed.
The mask itself still might have a response curve, but that doesn’t appear to be doing any harm to the image, at least in my setup.
Feel free to correct, as I’m finding this discussion to be very interesting
Having looked more closely at the way the 'divide' blend mode works, given that it's essentially taking the sampled colour & dividing by itself, producing white on the un-inverted negative rebate - thus we're probably ending up at a similar point from slightly different approaches.
Thank you PE! Good to get a clear answer from a reliable source.
And as usual the right citations are golden keys to unlock a cascade of great stuff.
https://www.osapublishing.org/josa/abstract.cfm?uri=josa-44-2-129
Tadaaki Tani, Photographic Science: Advances in Nano-Particles, J-aggregates and Dye Sensitization Page 188 bottom, also has a brief but good and illustrated explanation.
It's something I've never quite been able to wrap my head around. IE how a varying mask (not a simple filter) can be can be satisfyingly "removed" with a simple linear filter.
But that seems to be what is happening in the color enlarger/RA4 process..
Having looked more closely at the way the 'divide' blend mode works, given that it's essentially taking the sampled colour & dividing by itself, producing white on the un-inverted negative rebate - thus we're probably ending up at a similar point from slightly different approaches.
I knew there was a uniform orange filter to start with, in the undeveloped film, that affected the two underlying layers.It sounds as if you don't quite understand how the mask and orange color of a negative relate. They are not the same. The orange color of a negative is uniform, and consists of the non-uniform mask PLUS what it is masking: dye impurities.
The dye impurities form a negative image as PE has said, orange in color. The mask, formed during development, forms a positive orange image and its job is to mask, or cancel the dye impurity image.
Together, the two opposite images combine to form a UNIFORM orange cast all over the negative, overlaid over the main dye image. It is this uniform orange density that ends up being removed during printing or scanning, by simple filtering/color balancing, and along with it, the effects of the dye impurities.
The mask, cancelling the dye impurities of the negative, is beneficial for any use of the negative.
What I probably didn't quite get was how a positive image was formed...
I use a strobe diffused through a custom diffuser with enough separation between the film and the last diffuser stage that its completely out of focus and therefore a very smooth and diffuse light source. The strobe gives me very consistent and repeatable results, and I don't have to worry too much about light contamination because I'm operating at f/11 to f/16 at 1/250, which is easily several stops above the ambient room light. If the strobe don't fire, you get a black frame, when it does fire, you get the absolute minimum amount of anything that might introduce vibration induced blur. 35mm film can sometimes be a bit finicky with focus, especially if it's got a strong curl along it's longitude, but for that, I just go up to f/16-f/22 and turn the strobe power up. There's a little added diffraction, however, I'm using a very expensive macro lens, and with it, my setup is over 4000dpi for 35mm film. Jpegs scaled down to even a quarter of the resolution of the native sensor resolution have a *crazy* amount of fine detail. I'd rather have it in focus, than go for maximum sharpness and struggle with having frames in focus. For 120, there's close to 2 feet between the film and sensor. F/11 is plenty of DOF there. For me, going the DSLR route with custom software is a simple matter of speed. I can buzz through a freshly dry roll of 36 exposure film and be looking at the entire roll in LR in less than 15 minutes, with little to no retouching except for a spot of dust/fiber here or there, or the occasional scratch, and at most, some basic Develop Module touch ups if that.
Adrian, quick question about your scanning setup, if you don't mind sharing. What are you using for negative holders?
Enlarger negative carrier. If I'm going to make a print, it goes in the enlarger, if I'm going to scan it, it goes in the scanner. I can do single frames, or just run a whole roll through, and swap different carriers out for different film sizes, etc. Pretty handy, and quite gentle on the film.
It took some creative searching, but I found the right link:How can I find out about NLP and how it makes better conversions then those you listed?
I encourage anyone and everyone to watch the video in the link from PE. Most interesting piece of media I consumed in a long time.The "guys" are Wesley T. Hanson and Paul W. Vittum. The former has co-authored a major text on the subject as noted above.
https://ethw.org/Wesley_T._Hanson
PE
I find glassless holders and slide frames very overrated. It's far more important to have the negative as flat as you can. Glassless is never going to achieve that.This approach also works very well for DSLR macro scanning. I use a glassless negative carrier for that.
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