If you believe you can, or you believe you can't... you're right.
It appears you don't understand how an analog-to-digital (A/D) converter works.
Each value is related to adjacent values by a factor of two, exactly (at least theoretically).
That's the definition of a linear conversion function.
Devices that produce unique outputs when the inputs are varied by a factor of 2 are called "monotonic".
That's a desirable feature in commercial A/D converters, and is emphasized in their advertisements.
You can play with the design of the circuitry between the sensor and the A/D converter if you want some other conversion function, like logarithmic. But that's external to the A/D.
- Leigh
If you believe you can, or you believe you can't... you're right.
If you believe you can, or you believe you can't... you're right.
I have a section in my digital negative monograph posted on my website where I discuss the digital zone system, and have a figure showing zones, %K and corresponding pigment values. This may be what you are after.
Regards,
Mike
Mike,
How have you fared reading the densities of a negative using a scanner and how well did it correlate to the same negative read on a densitometer?
The problem I see is most scanners work to fit the range of the subject to nearly the entire positive scale 0-255, so a thin negative and a contrasty negative both give full-scale positive on-screen when the levels are adjusted. It's as if you had printed the thin neg on Grade 4 and the contrasty neg on Grade 2. But you know the densities of the two negatives aren't the same so there isn't a direct relationship from the 0-255 to a negative density from 0.00-3.00.
So to correlate a negative density to scanner result, you can scan a known grayscale and a test negative with the same parameters and compare different spots on both... There are probably other ways, and possibly some systems can directly provide a density reading.
But I don't see how you can directly relate 0-255 with 0.00 to 3.00 (or any other arbitrary density range) without some kind of calibrating.
Bill,
You're assuming that the scanner is going to do scaling, which is a post-scanning step.
The (few) scanners that I've worked with operate in raw mode, with the software doing any post-scan scaling.
In raw mode you certainly can correlate a specific level to a specific density.
The density range depends on the hardware, and will will vary from one device to another.
- Leigh
If you believe you can, or you believe you can't... you're right.
Thanks for all the ideas and opinions. Yes, one must first develop a standard in how the film is "always" scanned, and that alone will take some calibration using a step wedge, etc. For this to work with any level of accuracy, the scanner must to set NOT to scale the dynamic range of the negative automatically. That would throw the entire process of this off. My scanner is calibrated manually, using manual settings of black point, white point, etc. Using the Zone system, which I do, a given "Zone" from negative to negative should produce similar results and density on the film. Of course film testing and development testing must be done prior to this. For example, the 8 bit value measured, of say 120 will always result in the same "Zone", and consequently, the same approximate film density, if it were measured on the densitometer. Regardless if you way overexposed or underexposed the film, there will be density, and they will fall into a certain zone, regardless if you intended them to or not! This idea assumes all other variables are accounted for, proper exposure, proper development, and proper scanner fixed calibration for all negatives, as it should be. My settings, would probably not work for someone elses negatives, as some people interpret zones slightly different. Using the aforemented math, it works for me just fine now. If your scanner can not be set to raw or manual control (or the software), this will not work!
Great! I'm fortunate to use a real densitometer, and so I can verify (calibrate) what the scanner returns vs densities. Vue-Scan includes a densitometer tool that I occasionally experiment with but haven't calibrated yet.
Of course once you start watching your densities, you will start to see differences between what you expected and what you got.
Errors in exposure computation could cause all your Zones to fall on different densities than you expected (with no adverse impact on the "print-ability"). And flare totally plays havoc with where shadow Zone densities fall based on where you placed them (hopefully it improves them anyway).
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