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.
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.
In vuescan (pro version, advanced mode interface) in the Prefs tab, enable density display. Then pressing <Control> will display density values instead of RGB values at the bottom of the screen.Hi, Bernard....very interesting.
Just so I understand correctly - how did you calculate D from the scanner data?
For the V700, Preview: 400dpi, Scan 1600dpi. For the LS-2000, I put myself in the shoes of the naïve user: pressed "default settings" in the Input tab, then just changed from "Image" to "B/W negative" for the source.Also, why do you think there is such a discrepancy between preview and scan numbers - what are your resolutions for both.
One column out of 4 "does not look too bad". And maybe just changing one parameter somewhere in the interface would produce yet another column of discrepant results. Once I have calibrated my densitometer against two points on the Stouffer wedge, the agreement (my measurement versus the Stouffer data) agree within 0.02D up to 2.0D (from memory).Preview numbers on the V700 actually don't look too bad considering - particularly on the higher densities.
Thanks for the info regarding densitometer.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.
View attachment 294259
Not to be confused with "Number of samples", that combines a number of identical exposures to improve signal/noise; less effective IMO.
In vuescan (pro version, advanced mode interface) in the Prefs tab, enable density display. Then pressing <Control> will display density values instead of RGB values at the bottom of the screen.
For the V700, Preview: 400dpi, Scan 1600dpi. For the LS-2000, I put myself in the shoes of the naïve user: pressed "default settings" in the Input tab, then just changed from "Image" to "B/W negative" for the source.
As for the cause, I can only speculate. A proper documentation for software such as vuescan should include a signal processing diagram. Consisting of boxes (operations performed) and arrows (states of signal processing). Example of operation performed: normalize detector output to clear path (which is why the V700 film holder has a cutout at the top). Examples of states of signal: (1) black point has been set from sample of orange mask; (...) (2) processed according to scanner profile and expressed in AdobeRGB color space,(...). etc. Again, speculating, possibly Mr Hamrick does not maintain such a signal processing diagram. So, while densities should be computed as
-log10(Output/OutputClearPath),
maybe he applies the same formula to image data that is already partly processed. I have no motivation to embark into lengthy experiments to attempt to determine what is happening inside the black box just from the outside.
One column out of 4 "does not look too bad". And maybe just changing one parameter somewhere in the interface would produce yet another column of discrepant results. Once I have calibrated my densitometer against two points on the Stouffer wedge, the agreement (my measurement versus the Stouffer data) agree within 0.02D up to 2.0D (from memory).
Then again, one can produce very nice photos, including the technical aspect, just by empirical procedures, never dealing with densities and the like.
Thanks for the info regarding densitometer.
It would be like taking two camera pictures at the same exposure settings and combining them. Will you see more in the shadows?
Aren't you bracketing them at different exposure settings for HDR? That's different than a scanner where you can't change the exposure settings. It's fixed by its dMax designed into the machine.Yes, you can. I do it all the time with 2 or more exposures.
:Niranjan.
In vuescan (pro version, advanced mode interface) in the Prefs tab, enable density display. Then pressing <Control> will display density values instead of RGB values at the bottom of the screen.
In my version 9.7.37 64-bitThanks for the reply. I think I have the Pro version, but I can't find the Density option. Is it scanner specific - I have a different scanner, Epson Perfection 3200, which could be the reason, may be. Or may be it is the new upgrade. I have been putting off upgrading for a while. Needs more digging.
Aren't you bracketing them at different exposure settings for HDR? That's different than a scanner where you can't change the exposure settings. It's fixed by its dMax designed into the machine.
Nah! Dmax is fixed (limited) by at least two things.Aren't you bracketing them at different exposure settings for HDR? That's different than a scanner where you can't change the exposure settings. It's fixed by its dMax designed into the machine.
My conclusion: vuescan is worthless as a densitometer. And don't get me wrong: I use vuescan for all my scans.
You've explained it theoretically. The proof is in the pudding. I've never seen a multi-scan that someone presented in a forum that was better than a normal single scan adjusted with the shadow slider. Or the results were so slight, that it was;t worth the bother to scan multiple times and add them together, creating other issues they have to deal with.Nah! Dmax is fixed (limited) by at least two things.
Note in passing that for many scanners, the spec for Dmax assumes that quantization is the only limit, when in fact the electronic noise may make the performance worse.
- The electronic noise in the detector and analogue-digital converter; Ultimately, the limit is photon statistics.
- The quantization of the signal. Assuming a very old scanner with 8-bit A/D conversion, in the darkest parts, the outcomes of the A/D converter are like 0, 1, 2; from 1 to 2 is a 100% increase: coarse! At the other end (low opacity), one can separate 254 from 255, a 0.4% increase, nice!
If the density of the dark parts is more than 2.2 (approx) this means that even if the lightest parts register as 255 (good resolution) the darkest parts will be around 1 (maybe 2, or maybe 0).
Now assume you make a second exposure with 32x more exposure time. The CCD pixels will accumulate 32x more electrons. In the light parts, they will saturate; no prblem, because we already have good date for those. The dark parts will now register around 32, and the nearby values at 31 or 33, are only a 3% difference, much better than the 100% mentioned above.
Now in the computer, compute {First exposure}+(1/32)x{Second exposure}. Do this not in 8-bit, but in 32-bit arithmetic; with a few additional tricks to discard pixels that are saturated (second exposure) or have coarse resolution (first exposure).
Got it?
Doesn't increasing scan time only get you more noise in much the same way we get so much noise in night time cellphone pictures? We see this problem as we raise the ISO settings on a digital camera. More noise. The scanner's sensor similarly is over-driven producing noise. One has to assume that the manufacturer designed their scanner to scan at a speed that will produce the cleanest signals just as a digital camera produces the cleanest signals at it's optimal ISO, let's say 100. Otherwise, the manufacturer would be foolish not to slow it down a little and raise the Dmax specifications to get better results and sell the machine at a higher price. So if we artificially reduce the design speed, all we're doing is adding noise. IMO.
Noise in night-time digital pictures comes from increasing the ISO, either increasing the analogue gain or boosting the digital output (equivalent to sliding the right slider to the left, JUST BECAUSE you cannot increase the exposure time for fear of blurry pictures. Very long exposures (minute and more) suffer from another problem: unequal dark currents in pixels.Doesn't increasing scan time only get you more noise in much the same way we get so much noise in night time cellphone pictures?
Over-driven detector results in saturation, i.e. all high values registering the same maximum possible digital output. Not "noise".The scanner's sensor similarly is over-driven producing noise.
Once the number of bits of the A/D is chosen, say 12 in a middle-spec scanner, the D range in a single frame, single exposure, cannot exceed a limit, Delta-D=3.6 for 12 bits. Any slide approaching (say Dmax 3) this, and that is not clipped in highlights, will display posterization in the dark parts. Scanning speed is another issue: intensity of light source, size of CCD pixels, etc.One has to assume that the manufacturer designed their scanner to scan at a speed that will produce the cleanest signals
Can't argue with thatIMO.
How do you explain that same piece of film, same scanner, vuescan gives me readings differing by almost 1.0 in D among themselves, and from a proper densitometer? Sounds to me more than a linearity issue.As I said before. Vuescan will not be your problem (if you know how to use it).
Meaning a G-bar of 0.615 (0.8/1.3) might as well be 0.69 (0.9/1.3) or 0.54 (0.7/1.3) ?I my book, staying within 0.1D delta is anything but useless.
How do you explain that same piece of film, same scanner, vuescan gives me readings differing by almost 1.0 in D among themselves, and from a proper densitometer? Sounds to me more than a linearity issue.
Your explanations in that respect would be quite helpful.
Meaning a G-bar of 0.615 (0.8/1.3) might as well be 0.69 (0.9/1.3) or 0.54 (0.7/1.3) ?
Will slowing scan speed add noise to the shadow areas
or create other problems or not?
Does anyone have a multiscan combined result with a separate normal single scan result so we can compare the two?
I don't have Vuescan; only use Epsonscan on my V850. I don't want to waste time downloading a new program and learning it just to try someone's idea. If this is a viable procedure, certainly someone has some samples and has done a comparison they can show between multi and single-scan shots.How about doing it yourselves and proving either way.
I don't have Vuescan; only use Epsonscan on my V850. I don't want to waste time downloading a new program and learning it just to try someone's idea. If this is a viable procedure, certainly someone has some samples and has done a comparison they can show between multi and single-scan shots.
It would be unlikely that you would be able to see the difference once the results are uploaded on Photrio, or down-sized to fit on a 4K TV display.Does anyone have a multiscan combined result with a separate normal single scan result so we can compare the two?
If this is a viable procedure, certainly someone has some samples and has done a comparison they can show between multi and single-scan shots.
They could email me the original files in full resolution. Maybe they can post in full resolution just a part of the image where the shadow areas are although I would prefer a full picture.It would be unlikely that you would be able to see the difference once the results are uploaded on Photrio, or down-sized to fit on a 4K TV display.
If you made large prints, the differences are more likely to be visible.
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?