For the record this was a Stouffer Transmission Step Wedge sized 4x5 inches. According to the packaging it has 21 steps in "increments of .15".
If my math is correct, 21 steps amounts to a density range of 10.5 f/stops. 2 exp(10.5) = 1448, which in log (10) terms is 3.16.
Last edited by Ken Lee; 12-Jan-2018 at 11:17.
Most importantly if you look at those samples, yourself you see a reduction in noise, quite significant actually.
A simple method to view this is:
use a curve tool, to invert and brighten the darker steps. (adjust the intensity so yo can see the noise, I did about 75% on LAB scale)
If ken has time, and we are very lucky... he might post an example with vuescan, using an ideal typical exposure for BW negative stock. (using the method suggested earlier)
But before you rush out to rescan all your negs, remember this will only affect highlight or brighter mid tones in a dense negative. And a lot this probably disappears under the "weight" of 4x5, but very relevant to 35mm.
After applying a Gamma 2.2 correction to the VueScan raw file (not adjusted to level 3, the original scan), it seems that the VueScan values are somewhat more equi-distant than the Epson values. I guess this means the VueScan scan is more linear. But what if we apply a slight correction curve to the Epson scan: will any differences become negligible ?Originally Posted by Ted Baker
before you rush out to rescan all your negs
What does it suggest that the lowest VueScan values are shifted to the right ?
You need to careful that you don't jump to the wrong conclusion. You have applied a gamma to these, so they will not be linear, and they are not. It is also probable that the gamma 2.2 function you applied does not match sRGB gamma function applied in the epson scan. What this tests shows is what the dynamic range of the scanner is, and how to make a small, and possibly imperceivable improvement.
Interesting it matches with the silverfast paper.
That's to be expected as you have made 2.53 X (1.2 stops) exposure increase, but this is not a tonal change as all the tonal ratio's remain the same. What you are doing is keeping the highlights away from the noise floor.
This is screen shot of the last three steps at 85%, which is a pretty extreme example, but I can see the difference in noise.
Last edited by Ted Baker; 12-Jan-2018 at 03:51.
Why is it 2.3 stops ? steps are 1/3...
After applying a Gamma 2.2 correction to the VueScan raw file (not adjusted to level 3, the original scan), it seems that the VueScan values are somewhat more equi-distant than the Epson values. I guess this means the VueScan scan is more linear. But what if we apply a slight correction curve to the Epson scan: will any differences become negligible ?
What does it suggest that the lowest VueScan values are shifted to the right ?
Should both not be in the same colourspace, either sRGB or GrayGamma 2.2 to see a better evaluation?. My understanding is that sRGB and GrayGamma are 2 different beasts.
Careless on my part, Ken set the exposure time to 2.53 times increase, which I read as 2.3 the first time. I used stops out of habit.
Which I guess underscores the need to review the analysis.
2.53 X is a lot by the way, you won't be able to go that high normally. For 35mm fomapan 400 I use 2. The film has a fairly dense base. For hp5 on 120 1.2x is the max you can use. For 4x5 I measure it.
Its helpfull that they are in same colorspace. I converted vuescan to sRGB , and epson one to a linear scan, but could not find an easy way to post it here. Will try a bit harder tommorow.
Easy to fix, just replace the . by a /Careless on my part
Which I guess underscores the need to review the analysis.
2.53 X is a lot by the way, you won't be able to go that high normally. For 35mm fomapan 400 I use 2. The film has fairly dense base. For hp5 on 120 1.2x is the max you can use. For 4x5 I measure it., 2.3 to 2/3
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