View Full Version : Scanner performance - v700 and Vuescan Pro - in relation to step wedges
Greetings,
I recently scanned some photos trying to get an idea of how dense various parts of the negative really were in an attempt to evaluate my workflow so that I was making negatives that could be either scanned or optically printed one day. I came across a result that made me think about how much influence the software driving the scanner was making. To try to eliminate the scanner software I thought of making a scan with significantly large areas of clear glass and black matting. Those two areas (if significant in size) would be treated by the scanner software as the upper and lower bounds - the two ends of the histogram.
I assume the software will interpret any value in between in a linear fashion. I have turned off all controls on the scanner software and scan to a non-compressed tiff file. Scanning as a 16bit per channel -vs- 8bit per channel has no bearing on the density range. Exactly the same graph will result with a heck of a lot more shades of grey in between.
To relate the scanner results to real life I scanned a calibrated 4x5 Stouffer step wedge that has 31 steps.
Attached to the post are three pdf files. One of a step wedge with areas of clear glass and black matting, one of just the 4x5 step wedge itself and one graph showing the difference between the two.
Six observations / conclusions:
A. The scanner begins to be non-linear at about a density of 1.75 to be generous. This would mean (to me) that one should not develop a negative to a density of greater than 1.75 or so to linearly digitise it. In reality we might choose to go beyond this a little.
B. The scan that has the absolute limits set seems to have a more linear response. It may not matter in reality. Certainly, the histogram in Photoshop has room to move for the slider at the high and also at the low ends. To me a scan that establishes the 'absolutes' of 'white' and 'black' is one that does have much less capability of software interpretation.
C. The film enthusiast should not develop film to have a greater density than about 1.75 if they wish to have a linear scan made to digitise their image.
D. To check the neg density range make sure to scan with large enough clear glass and use a black matt. The digital values -vs- densities are clearly seen in the results I've posted (assuming softwares and scanner hardwares produce a similar result ...)
E. A scanner will scan a bit more density range (linearly) than one could print optically without dodging and burning. Straight print -vs- straight (linear) scan the scanner has more range but only just. A diffuser enlarger density range of 1.2 is a digital range from around 220 (density of ~1.47) to 40 (density of ~0.27) on the chart.
F. Given the fact of (E) one can expose generously and pull development (with a goodly strong developer) knowing that in the event of a slightly denser negative, it is able to be scanned very well. Low density negatives cannot be rescued by either digital scanning nor optical printing.
One question:
How, on the basis of these results, can a scanner manufacturer claim to be able to scan a density of 4.0 ??? The scanner is blocked up at 255 with a density of around 2.4 ! (and it is highly non-linear from 2.0 ...) Perhaps the only thing I can think of is the 'exposure' setting (if there is one). Perhaps letting the CCD collect more light over a longer period of time ? Given my question, it makes no sense whatsoever to buy a higher end scanner based on the 'fact' that it can scan to some fictitious density ...
If others could post their results from their step wedges it would be a great comparison. I'll go out on a limb and bet the results will be very similar across scanners and softwares which means if people include large areas of clear glass and also use a black matt they can interpret their digitised results pretty accurately (no need to buy a Stouffer step wedge after all ...).
And BTW I have contacted Epson about their Epson scan software that is limited in its file size. I have asked them to consider those of us who would scan the whole glass platen without limitations but I don't think they'll change. I think too the Digital ICE might only work on small film sizes in the Epson film holders.
All to the good !
Cheers,
Steve
Ken Lee
30-Mar-2016, 17:24
http://www.kenleegallery.com/images/forum/EpsonV700StepWedge.jpg
Here's a scan of a Stouffer Step Wedge on an Epson V700 using Epson Scan software. This test suggests the scanner can distinguish around 16 steps, which means 8 stops of dynamic range. In log terms, this is around 2.4, which should be adequate for b&w film exposed and developed normally.
When I asked Sandy King about this, he pointed out that color transparency film can reach densities over 3.0, so for challenging color work this scanner may not be the best option.
I don't know how linear the result is, but can't that be corrected fairly easily if we apply an appropriate correction curve ?
Interesting ...
I believe Sandy is correct in that colour slide gets seriously high densities. I have the same sort of figure (3.0) in mind for Velvia.
On the scan above you have no detail at either end ! How did you achieve that ?!
:-)
Ken Lee
31-Mar-2016, 02:49
On the scan above you have no detail at either end ! How did you achieve that ?!
I made that test 4 years ago, but I presume I simply used the Histogram tool in the scanning software, setting the black point to the clear film edge and the white point so that the dense area which makes up the background of the image is pure white, with no further clipping.
The process is described in this article (http://www.kenleegallery.com/html/scanning/index.php). Using Epson Scan software, it's very easy.
Once you adjust the black and white points, you can control the linearity to some degree by adjusting the Gamma setting. I'm not sure what I used back then. Presumably a Gamma of 1.0 gives a linear scan, but I have not tested this.
The image I posted here is not perfectly linear. If the scanner can discern 16 steps, the resulting image should contain 16 evenly spaced steps reading 0, 15, 31, 48, 63... 255. However, in Photoshop they read 0, 5, 31, 55, 77 etc.
We could make a correction curve in Photoshop to linearize the values.
vuescan
31-Mar-2016, 07:00
Hi,
Just been reading through this. I look after the marketing for VueScan - so cannot say anything at all about this technically (sorry!) but if you did want me to ask Ed Hamrick anything in particular just let me know. Happy to get his opinion on something if that would help??
Regards,
Beverley.
I assume the software will interpret any value in between in a linear fashion. I have turned off all controls on the scanner software and scan to a non-compressed tiff file. Scanning as a 16bit per channel -vs- 8bit per channel has no bearing on the density range. Exactly the same graph will result with a heck of a lot more shades of grey in between.
Perhaps you scanned a negative in negative mode. If you want to get linear readings, you have to turn linear mode on (scanning gamma=1.0).
I've published my densities from IT8.7 target here: https://sites.google.com/site/negfix/scan_dens (Epson V750)
JaZ
Hi JaZ99,
My readings are very linear up to a point I should say, but could you enlighten us on this 'linear mode' ?? Where does one "turn on linear mode" ? I see, 'Image', 'Slide film', 'Color negative', 'B/W negative' and 'Microfilm' and it has to be one of those choices !
I'm all for a process that is fully explained and transparent as possible in that what I want is a WYSIWYG response to my scanning. What I see on film is translated to a digital file without any interpretation.
Ken,
Any curve you make would have to counteract the curve put in there by the scanner response as I understand it. You'd have to essentially generate a polynomial of the scanner response and counteract it. I reckon with electronics being so stable it would be possible for the manufacturer to publish such a polynomial but I can't see it happening. It may even be as simple as a response curve from any other CCD type device - I don't know. All I've ended up doing so far as I know is pin the extremes (black and white) to the extremes of the digital range (0 and 255) and I hope that the scanner software will just linearly sample all the shades in between.
I have done this in practice with a real photo and can say that the scanner software output is dramatically different when the 'absolutes' as I call them are not included in the first high-resolution scan. I do admit that first scan is a huge file but the first action in Photoshop would be to trim it to size leaving all the values intact. I've created files larger than 3.5G for 4x5 so Photoshop CS6 goes to this size at least !
To me, there is no sure footing to the purity argument when you don't know for sure that you are eliminating the assumptions in the software. For me, the whole 'purity' argument falls flat when the process is not known. My art is actually going to be mine and Ed Hamrick's and Epson's art coz they all had a hand in making it and they all acted independently from each other without the other one's knowledge.
Hi Beverley,
I think what would be excellent would be for Ed to enlighten us on how to do an absolutely straight scan that does not interpret anything at all in the image. JaZ99 speaks of a 'linear' mode - so far, I can't find the word 'linear' anywhere in the settings of Vuescan (version 9.5.25 on Linux - professional mode)
Even better would be a simple document enlightening us to the process by which a scan is made so that we can choose our options in an informed way. The document simply need to address the concerns of the LF community which are in the main a desire for high accuracy and purity of result I guess. People here are worried about the process and not just whether the final result is pleasing to the eye.
I would also say there are features that Ed could explain for us like Digital ICE and whether it works (or why it doesn't) and the 'density display' option for starters.
Cheers all.
Hi JaZ99,
My readings are very linear up to a point I should say, but could you enlighten us on this 'linear mode' ?? Where does one "turn on linear mode" ? I see, 'Image', 'Slide film', 'Color negative', 'B/W negative' and 'Microfilm' and it has to be one of those choices !
I'm all for a process that is fully explained and transparent as possible in that what I want is a WYSIWYG response to my scanning. What I see on film is translated to a digital file without any interpretation.
Linear mode is the mode when the scanner works in linear fashion, that means, the scanning gamma is 1.0. Since you are using Epson scan you are out of luck, I'm afraid.
Perhaps you can try to linarize the scanned data with new_gamma=1/scanning_gamma.
djdister
1-Apr-2016, 05:58
Linear mode is the mode when the scanner works in linear fashion, that means, the scanning gamma is 1.0. Since you are using Epson scan you are out of luck, I'm afraid.
Not true. Epson Scan allows you to use a straight (linear) gamma or alter it as you wish. It is not however termed "linear mode" so anyone looking for such a button to click will not find one.
Not true. Epson Scan allows you to use a straight (linear) gamma or alter it as you wish. It is not however termed "linear mode" so anyone looking for such a button to click will not find one.
Last time I've checked there were two gamma settings only: 1.8 and 2.2. But it was a few yers ago, newer looked back at Epson Scan again. Good to know they update the software.
djdister
1-Apr-2016, 07:16
Last time I've checked there were two gamma settings only: 1.8 and 2.2. But it was a few yers ago, newer looked back at Epson Scan again. Good to know they update the software.
When using Epson Scan in Professional mode, the Histogram Adjustment button provides a graphical interface for adjusting highlight, shadow, and gamma levels individually.
I've published my densities from IT8.7 target here: https://sites.google.com/site/negfix/scan_dens (Epson V750)
Was your IT8.7 target a transparency, or did you scan a reflected target ?
Does the Epson Scan software allow profiling with an IT8.7 target ?
Silverfast scanning software allows calibration via a target, according to http://www.filmscanner.info/en/Scannerkalibrierung.html (http://www.filmscanner.info/en/Scannerkalibrierung.html)
Was your IT8.7 target a transparency, or did you scan a reflected target ?
Transparency (Ektachrome)
Does the Epson Scan software allow profiling with an IT8.7 target ?
No. I've got Monaco EZ Color shipped with my scanner, but the scan was not profiled for this particular purpose. It was clean, linear scan.
Silverfast scanning software allows calibration via a target, according to http://www.filmscanner.info/en/Scannerkalibrierung.html (http://www.filmscanner.info/en/Scannerkalibrierung.html)
It does. And when I compared (http://www.iccview.de/) color space of profiles made by EZ Color and Silverfast, I stopped using SilverFast calibration.
When I compared (http://www.iccview.de/) color space of profiles made by EZ Color and Silverfast, I stopped using SilverFast calibration.
I don't speak German, but apparently that site allows you to compare ICC profiles. What difference did you see please ?
From what I can tell, the Monaco EZColor product is no longer sold. Aside from Silverfast, are there other tools available for calibrating Epson flatbeds ?
Peter De Smidt
1-Apr-2016, 09:55
From memory, Silverfast does not allow creating IT8 targets for different emulsions. They only allow a generic profile. If that's right, it's a huge minus. The profile needed for, say, Velvia 50 is quite different from one needed for Ektachrome. When scanning slides, I use as unprocessed a scan as possible. When bringing the file into photoshop, I apply the proper IT8 profile and then convert to the editing space. On Wolf Faust's recommendation, I used Lprof to make the profiles.
Are these profiles mainly useful for overcoming the irregular color casts of various film stocks ?
I am interested in B&W linearization: getting a linear scan of an already linear Stouffer step-wedge.
Peter De Smidt
1-Apr-2016, 12:15
Are these profiles mainly useful for overcoming the irregular color casts of various film stocks ?
Yes, that's right.
Yes, that's right.
It depends on quality of light source of the scanner.
I've got different IT8.7 targets and scanned on 2 scanners. The results are here: http://jaz99.blogspot.com/2016/01/metamerism-and-scanners.html
Ken,
Various calibrated colour transparencies available from Wolf Faust at Coloraid.de I have the 4x5 Fuji Velvia and Astia ones. You buy for the film stock you need to scan.
Extremely easy to calibrate your v700 with professional Vuescan because Vuescan has a special routine that detects the target.
Simply buy the target for your film and Vuescan and you're done. Only works on Windows / Mac though I think.
Wolf is a very competent and professional person. The product is exceptional.
jaZ99 - I'm using Vuescan Pro and have done so for a decade. I mentioned Epson Scan in my post as I have it installed also but don't use it. I haven't paid for a 'pro' version I just have a version that came with the scanner.
:-)
Hey Peter !
Can I ask if you are using LPROF with Vuescan on Linux ?
I haven't looked for a long while but I would like to be able to scan with a calibrated monitor and calibrated scanner on Linux if I could. I've just loaded the latest nightly build of GIMP with its increased bit depth but it crashed on my first try ...
TIA
Peter De Smidt
2-Apr-2016, 05:30
Hi,
I scan with Colorgenius V2 on a very old Mac. Profiling is done on a Windows machine.
I decided to revisit the issue. Using Epson Scan software, here are 2 scans of a Stouffer 21-step Transmission Projection Step Wedge.
The input sliders have been adjusted to render Step 1 at 0 and Step 21 at 255.
With the Gamma set to 1.0, we can see all the steps, but they are not linear: the low values in particular are poorly separated.
http://www.kenleegallery.com/images/forum/StoufferGamma1.jpg
With the Gamma adjusted to 1.5, we get improved separation in the low values, but the image isn't linear.
http://www.kenleegallery.com/images/forum/StoufferGamma15.jpg
I am pleasantly surprised to see that the scanner can distinguish all the steps. Since the guide has 21 steps, each equivalent to 1/2 f/stop, this means we are able to discern a range of 10 f/stops. According to the Stouffer web site (http://www.stouffer.net/Photo.htm), the Dmax of the step wedge is 3.05.
Perhaps the scanner can exceed that number: I can't tell without a target of longer density range.
I tried making an Adjustment Curve in Photoshop to make the results perfectly linear - such that the steps are evenly distributed - but got tangled up in the process. Each time I added a point to the curve, it changed the adjacent tones. Can anyone recommend an easy method ?
Peter De Smidt
3-Apr-2016, 08:06
Ken, you don't develop your film to a max density of 3.05, do you? It's probably around 1.4 (or so). I'd ignore results above, say, 2.00 unless you know that your negatives will be that dense. Personally, I'd leave it alone. It should be linear enough. I'd adjust the file to how you want it to look via Photoshop or other editing program. Whenever you apply a curve, you'll lose some of the gray tones in the image, as some of them will inevitably merge. Once merged they don't come apart again, at least they don't with global image adjustments. For all you know the look you want is the opposite of whatever correction curve you want to do....
But if you really want to do this, simply make a tone curve in Vuescan, or apply one in Photoshop, that makes the scan more linear. Mind you, this will only really work for one film type, developed in the same way, and exposed in the same way. I really wouldn't bother.
I like that last statement ! Thank you for pointing out that any curve we make for the Stouffer step wedge would be inappropriate for negatives developed to other levels of contrast !
I've never bothered with this issue in the past because even if we get a perfectly linear scan, we usually add an adjustment curve for aesthetic reasons.
Hello -
Thanks for getting back to me. Have sent your request on to Ed - we won't forget it so don't worry if it takes a while. Just busy adding new scanners at the moment....
Best wishes,
Beverley.
Hi JaZ99,
My readings are very linear up to a point I should say, but could you enlighten us on this 'linear mode' ?? Where does one "turn on linear mode" ? I see, 'Image', 'Slide film', 'Color negative', 'B/W negative' and 'Microfilm' and it has to be one of those choices !
I'm all for a process that is fully explained and transparent as possible in that what I want is a WYSIWYG response to my scanning. What I see on film is translated to a digital file without any interpretation.
Ken,
Any curve you make would have to counteract the curve put in there by the scanner response as I understand it. You'd have to essentially generate a polynomial of the scanner response and counteract it. I reckon with electronics being so stable it would be possible for the manufacturer to publish such a polynomial but I can't see it happening. It may even be as simple as a response curve from any other CCD type device - I don't know. All I've ended up doing so far as I know is pin the extremes (black and white) to the extremes of the digital range (0 and 255) and I hope that the scanner software will just linearly sample all the shades in between.
I have done this in practice with a real photo and can say that the scanner software output is dramatically different when the 'absolutes' as I call them are not included in the first high-resolution scan. I do admit that first scan is a huge file but the first action in Photoshop would be to trim it to size leaving all the values intact. I've created files larger than 3.5G for 4x5 so Photoshop CS6 goes to this size at least !
To me, there is no sure footing to the purity argument when you don't know for sure that you are eliminating the assumptions in the software. For me, the whole 'purity' argument falls flat when the process is not known. My art is actually going to be mine and Ed Hamrick's and Epson's art coz they all had a hand in making it and they all acted independently from each other without the other one's knowledge.
Hi Beverley,
I think what would be excellent would be for Ed to enlighten us on how to do an absolutely straight scan that does not interpret anything at all in the image. JaZ99 speaks of a 'linear' mode - so far, I can't find the word 'linear' anywhere in the settings of Vuescan (version 9.5.25 on Linux - professional mode)
Even better would be a simple document enlightening us to the process by which a scan is made so that we can choose our options in an informed way. The document simply need to address the concerns of the LF community which are in the main a desire for high accuracy and purity of result I guess. People here are worried about the process and not just whether the final result is pleasing to the eye.
I would also say there are features that Ed could explain for us like Digital ICE and whether it works (or why it doesn't) and the 'density display' option for starters.
Cheers all.
Hi,
Ref: VueScan - Yes, it’s the same focusing mechanism as is used in Epson Scan.
And to get an absolutely unmodified scan, with gamma 1.0
(which is what comes from the CCD of the scanner), simply
set “Output | Raw file”
I hope that helps....
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