Dmax App

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Annette Fazzari

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Aug 4, 2024, 2:44:43 PM8/4/24

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DMaxis the maximum density that a) occurs in a film or print, or b) that can be distinguished from black by a scanner or densitometer or whatever device. It is a single number representing a single density.

Dmin is the minimum density etc. etc. that can be distingished from pure white - i.e. a slide film might have a Dmin of say 0.1 - totally fog the film with light and the plastic base and emulsion together (film base + fog) will register 0.1 darker than pure white light, on a densitometer.

An example: if a slide film has a DMax of 3.0 - a scanner with a DMax capability of 3.0 or higher should (!) be able to 'see' all the details in the film (i.e. distinguish them from pure black), while a scanner with a "DMax" of say, 2.8, will lose any details between 2.8 and 3.0 - they will all just record as more black area because the device can't sense the tiny amounts of light getting through.

From a practical point of view, when scanning, I think the answer is as follows. Dmax is the highest density in the film which can be captured by the scanner. All values above that will give essentially the same response. Dmin is the lowest value that can be recorded by the scanner. Drange is the difference between the two.

Most people prefer slides. This is without any good basis as far as I'm concerned, but I doubt if I am going to convince anyone of that. Slide film is designed to produce relatively high densities in the film because of the way it is viewed. If one overexposes even slightly that will excacerbate the situation. In such cases, the densities in the shadows will exceed what many moderate priced scanners can handle. For example, Epson says my 3200 scanner has a dmax of 3.4. I use Vuescan which allows me to read the actual densities as well as the usual RGB values. I'm not sure these are the same as would be read by a precision densitometer, but they seem pretty consistent with what I would expect from years of experience with film of all sorts. My slides often have maximum densities of 3.0 or higher, but not beyond 3.4. Thus from my perspective, Epson's advertised value is accurate. I don't usually have any trouble with the scans from those slides. But I'm very careful about exposure.

For slides, I readily sacrifice the shadows if necessary in order to get proper exposure for the highlights. That is the conventional view of how reversal film should be used. One should avoid scenes with extreme contrasts and if that can't be avoided, concentrate on getting the highlights and midrage properly exposed, which means one may lose some detail in the shadows. But if one uses slide film with the intention of scanning, there is an additional option. One may overexpose somewhat, thus preserving both highlight and shadow detail. (One can't overdo this since slide films tend to have limited latitude for exposure.) The resulting slide won't be ideal for direct viewing, but when scanned, if the scanner has a high dmax, one may produce a scan with adequate detail at all levels. A scanner like the Epson 3200 may not be adequate for such slides.

I'm not sure why you think using software to remove the orange cast is going to degrade the image. I have to think about exactly how they might go about it, but, offhand, it seems to me the change must be completely reversible and that no information in the image is lost. But I will give it some thought. Perhaps someone else who has thought about it can comment.

In fact, it seems to me you would degrade the image more if you used a filter in the optical system to do it. The optics of the filter would play a role. You certainly don't want anything in the optical path you don't have to have there.

I've now thought a bit about what must be done to remove the orange mask by the scanning software. Clearly you have to add sufficient complementary color, mostly cyan, to negate it. That would mean adding to the blue and green channels. If the maximum densities in those channels were already quite high, one would run the risk of pushing the maximum densities in those channels too high and would thereby lose some information. But in fact, negative material characteristically have relatively low maximum densities, compared to slides and what modern scanners can handle. So the net effect is to shift the shole range of densities upward without any information being lost at the high end.

Tghe issues you raise about gaps in the histogram are another matter. Theoretcially, one should tailor the film to the scanner so the full range of the scanner is utilized. But in practice, if one is scanning at 16 bits per channel, there is more than enough extra capacity built in that the spreading of values and attendant problems aren't in fact a problem.

Ive just had my isuzu dmax 2016 plate converted to a tipper and when i went to pick it up a major fault has developed and I cannot get out of 4 wheel drive. The circle electronic dial changes between 4 low and 4 high fine but when i turn it to 2 wheel drive it whirs and you can hear it trying to change to 2 wheel drive but it doesnts. It whirs again and on the dash it changes to 4 low drive. This is doing my head in, is this something that anyone knows anything about? Could it be something to do with the earth from the tipper ram of the alterations in wiring that have gone on to the rear lights with the tipper body being put on? Or has it somehow got stuck as its been sat for a month and a half???

thanks for the suggestions both, ive tried these extensively now and cannot get it to shift into 2 wheel drive, i think it may need the transfer box/solenoid that switches between 4l/4h/2h fiddling with or new one potentially?

Its common when someone has been on hard ground and been turning.. as others say. Get on soft ground (grass) and try.

on my old pajero, for 4wd to 2wd high ratio, I had to decelerate and accelerate hard on hard ground. But it would not work unless going straight..

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