VueScan as densitometer: how to calculate the CI?
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I would be cautious before believing density measurements from vuescan. You might perform a simple experiment: measure the density of two pieces of film (of uniform opacity) separately, d1 and d2. Then stack them in the film carrier and check that the measured density is d1+d2. That is simple in principle, but there are details. Like, no piece of film has a constant density across, because of grain. To address this, you can either eyeball a spatial average as you move the cursor across, or purposely defocus. Too bad vuescan does not allow to define the probe size, like, e.g. 9x9 pixels.
What is the CI?
Contrast Index.
You have the H-D curve plotted off the measurements?
Nope. Im not even sure what that is.
Im trying to develop a negative (TMY2) with a CI at 0.54 using Pyrocat: http://www.sandykingphotography.com/resources/technical-writing/pyro-staining-developers
In the article though... it is referred to CI and G as the same thing (as far as I can understand), while this being slightly two different things.
Oh you want exposure vs density? Yeah I got it. I don't know about the software but it must not alter the contrast. Many scanning software can alter the contrast.
H-D curves are plots of D (density) vs Log E (exposure). CI is the slope of the linear part of that curve.
Check out this video that explains how to do it:
Check out this video that explains how to do it:
Doesn't Epsonscan do it too?
The G is for G bar, not gamma. Which makes sense.
VueScan as densitometer has been explained by (I recall?) Ed Hamrick himself. Google might be our friend.
I doubt anybody would bother with Epson-as-densitometer, given the expertise of VueScan user base. Try it...no reason it shouldn't work.
Can anyone comment on using Silverfast 9 as a densitometer? With or without some sort of step wedge.
Thanks.
Thanks.
You're the guy who asked the Epson question.
Ask the Epson user base. If there's no help that may explain VueScan enthusiasm.
MattKing
Moderator
The point is that in some cases you may be able to use a scanner to perform the function of a densitometer, and thus negate the need to have a densitometer.
For those of course who make use of densitometers.
For those of course who make use of densitometers.
OK. I get your point.
But really. How is one served using a densitometer? Would it help me when I scan?
MattKing
Moderator
Knowledgeable use of a densitometer can help you monitor the technical qualities of your slides and negatives, including the development your labs provide you.OK. I get your point.
But from what you post here about what you like to do, I can't see much benefit for you.
I've only used one regularly while working in a colour printing lab, and that was to monitor control strips.
Any for the extremely infrequent and rare times I have needed to objectively measure the density of film (transmission densitometer) or the tone in a test strip (reflection densitometer) I have friends do that for me.
If you want to do manual calculation from a scan - convert the RGB data to L*ab by using this:
http://www.brucelindbloom.com/index.html
and then from L* to D as explained here:
https://sites.google.com/site/negfix/scan_dens
:Niranjan
http://www.brucelindbloom.com/index.html
and then from L* to D as explained here:
https://sites.google.com/site/negfix/scan_dens
:Niranjan
Thanks for the info. It seems I wouldn't need to know the density of my film since I have it developed by a lab.
I'm curious though. When I shoot Velvia, the shadow areas are very opaque. Would any of these measurement procedures help me get better results from my scans?
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Unfortunately no, IMO. Not anymore than looking at a thermometer will make the cold more bearable.
What might help you, though, is a feature of vuescan (possibly present in other software) called Multi Exposure, whereby the image is digitized twice: (a) with a moderate exposure limited by not "burning through" the transparent parts of the film, (b) second one with a longer exposure time and/or higher analog gain, to improve the signal/noise in the opaque parts; the two exposures are then combined into a single digital image with a higher dynamic range than might be achieved with either one alone. Need to store the result as 48-bit Tiff in order to reap full benefit.
Not to be confused with "Number of samples", that combines a number of identical exposures to improve signal/noise; less effective IMO.
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VueScan as densitometer : Don't even think of it.
This thread prompted me to perform experiments that confirmed my suspicions. Test object: a 35mm b/w image of the Kodak Gray Scale in the Professional Photoguide. Just to avoid spurious arguments: I'm aware that the reflection densities are tricky because of specular reflections; the gray scale patch numbers are for reference only. What matters is that the same piece of film with various density patches was measured in various ways. With two different scanners, in Preview and after Scan. Then with a Macbeth TR1224 densitometer.
Legend: GSP: GrayScale Patch number on the Kodak card, again for reference only. V700-Pre: measurement after preview. V-700-Sc: after scan. Ditto for Nikon LS-2000.
The anomalous readings (higher density) for the "2.2" patch are not too surprising: being in a corner of the gray card, it may have been affected by specular reflection. When I use this card in other measurements, I discard the two darkest pactches for that same reason, and I use my measured values for the reflection densities of the other patches. The true (TR1224) densities are fairly high just because I happened to choose a frame exposed at +3EV; they are still well within the range where proper density measurements should be expected.
The vuescan density readings were jumping around by at least +/-0.05 depending on the probe position; I did not bother to attempt some kind of averaging because (a) probe size and averaging should be an option in a well designed tool; (b) the discrepancies between columns are an order of magnitude larger.
The TR1224 was calibrated using a Stouffer T3110 (calibrated) wedge. Anyway, the re-calibration from the previous Eprom-stored values involved changes of 0.01D.
My conclusion: vuescan is worthless as a densitometer. And don't get me wrong: I use vuescan for all my scans.
This thread prompted me to perform experiments that confirmed my suspicions. Test object: a 35mm b/w image of the Kodak Gray Scale in the Professional Photoguide. Just to avoid spurious arguments: I'm aware that the reflection densities are tricky because of specular reflections; the gray scale patch numbers are for reference only. What matters is that the same piece of film with various density patches was measured in various ways. With two different scanners, in Preview and after Scan. Then with a Macbeth TR1224 densitometer.
| GSP | V700-Pre | V700-Sc | LS-2000-Pre | LS-2000-Sc | TR-1224 |
| 0.1 | 1.82 | 0.98 | 2.62 | 1.80 | 1.71 |
| 0.4 | 1.72 | 0.84 | 2.64 | 1.62 | 1.63 |
| 0.7 | 1.58 | 0.66 | 2.36 | 1.36 | 1.47 |
| 1.0 | 1.46 | 0.56 | 2.20 | 1.22 | 1.37 |
| 1.3 | 1.30 | 0.38 | 1.96 | 1.10 | 1.23 |
| 1.6 | 1.10 | 0.22 | 1.74 | 0.76 | 1.08 |
| 1.9 | 1.02 | 0.12 | 1.68 | 0.72 | 1.02 |
| 2.2 | 1.08 | 0.20 | 1.72 | 0.80 | 1.05 |
The anomalous readings (higher density) for the "2.2" patch are not too surprising: being in a corner of the gray card, it may have been affected by specular reflection. When I use this card in other measurements, I discard the two darkest pactches for that same reason, and I use my measured values for the reflection densities of the other patches. The true (TR1224) densities are fairly high just because I happened to choose a frame exposed at +3EV; they are still well within the range where proper density measurements should be expected.
The vuescan density readings were jumping around by at least +/-0.05 depending on the probe position; I did not bother to attempt some kind of averaging because (a) probe size and averaging should be an option in a well designed tool; (b) the discrepancies between columns are an order of magnitude larger.
The TR1224 was calibrated using a Stouffer T3110 (calibrated) wedge. Anyway, the re-calibration from the previous Eprom-stored values involved changes of 0.01D.
My conclusion: vuescan is worthless as a densitometer. And don't get me wrong: I use vuescan for all my scans.
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