Q-dog
Established
I use vuescan and a Scan Dual II for scanning negatives, both bw and colour. I pretty much follows the method described in the vuescan manual under "advanced workflow", ie I scan a blank frame, lock exposure and film base colour and then scan the whole roll. This gives usable images but not great. (Well, it might be that the negatives aren´t great...).
What bothers me is that the histograms covers only a small area of the x-axis. I would imagine that to get maximum out of the scan the histograms should go almost from end to end without clipping. But when I look at the vuescan "raw" histogram it covers only about 10% of the x-axis. The "b/w" histogram covers more but not more than 50%.
Am I doing something wrong?
What bothers me is that the histograms covers only a small area of the x-axis. I would imagine that to get maximum out of the scan the histograms should go almost from end to end without clipping. But when I look at the vuescan "raw" histogram it covers only about 10% of the x-axis. The "b/w" histogram covers more but not more than 50%.
Am I doing something wrong?
bmattock
Veteran
I do not know, but it almost sounds to me as if you are seriously over or under exposing, or if your ScanDual II is malfunctioning.
I used to follow the 'advanced workflow' pretty religiously, but overall, I tend to just take the 'defaults' now for nearly everything - and find I'm happier overall. Still, my images always need some touchup in an editing program (I use The GIMP). Nature of the beast.
Getting back to your histogram - I use the B/W histogram because it has sliders I can manipulate - the 'raw' does not, as I recall.
I find that if my film is seriously underexposed, the histogram is all bunched up on the left - if overexposed, it is all bunched up at the right.
This does not always mean that your exposure or development are at fault, however. All scanners are not created equal - some have lower DMAX than others, and will have more trouble seeing through dense negs. Such scanners would tend to see film negatives as overexposed fairly easily. With such scanners, slight underexposure may give you a better scan.
If you take the 'default' settings (non-exposure locked), do you get better results? If so, then I'd do that. This is what I eventually settled on. I just experimented and used what seemed to work best for me, which turned out to not be the 'lock exposure' setting.
I used to follow the 'advanced workflow' pretty religiously, but overall, I tend to just take the 'defaults' now for nearly everything - and find I'm happier overall. Still, my images always need some touchup in an editing program (I use The GIMP). Nature of the beast.
Getting back to your histogram - I use the B/W histogram because it has sliders I can manipulate - the 'raw' does not, as I recall.
I find that if my film is seriously underexposed, the histogram is all bunched up on the left - if overexposed, it is all bunched up at the right.
This does not always mean that your exposure or development are at fault, however. All scanners are not created equal - some have lower DMAX than others, and will have more trouble seeing through dense negs. Such scanners would tend to see film negatives as overexposed fairly easily. With such scanners, slight underexposure may give you a better scan.
If you take the 'default' settings (non-exposure locked), do you get better results? If so, then I'd do that. This is what I eventually settled on. I just experimented and used what seemed to work best for me, which turned out to not be the 'lock exposure' setting.
kaiyen
local man of mystery
One issue might indeed be development and exposure. Another is to adjust the film profile and CI. However, that really only helps with the highlights. I can bring them back by using .70 or .80 if needed. I usually use .55.
If your shadows are towards the middle, then you've over exposed.
allan
If your shadows are towards the middle, then you've over exposed.
allan
vicmortelmans
Well-known
Hi,
I also started using Vuescan with as few automatic features as possible. This drastically improves scanning speed, but experience shows that there's little gain... After a couple of rolls, I set it back to automatic exposure, so Vuescan does a preview scan of each slide and sets exposure accordingly.
Note that a very wide raw histogram is not good either: your highlights will be in the region where scanner noise starts causing trouble and because scanner data is linear, contrary to densities, which are logarithmic to ligth intensity (as is the eye), there's very little relevant information captured from very high densities. That's why scanners tend to like somewhat underdeveloped negatives.
Groeten,
Vic
I also started using Vuescan with as few automatic features as possible. This drastically improves scanning speed, but experience shows that there's little gain... After a couple of rolls, I set it back to automatic exposure, so Vuescan does a preview scan of each slide and sets exposure accordingly.
Note that a very wide raw histogram is not good either: your highlights will be in the region where scanner noise starts causing trouble and because scanner data is linear, contrary to densities, which are logarithmic to ligth intensity (as is the eye), there's very little relevant information captured from very high densities. That's why scanners tend to like somewhat underdeveloped negatives.
Groeten,
Vic
Q-dog
Established
Thank you all, for your replies.
Indeed it seems that I get a better result when using automatic exposure. But the raw histogram is still very much to the left. And I don´t think my exposure is that much off. I will try to find some negatives that I know are under / overexposed and see how they come through.
What I don't understand is that while the raw histogram is clipped to the left the "b/w" histogram doesn't look clipped at all.
Ola
Indeed it seems that I get a better result when using automatic exposure. But the raw histogram is still very much to the left. And I don´t think my exposure is that much off. I will try to find some negatives that I know are under / overexposed and see how they come through.
What I don't understand is that while the raw histogram is clipped to the left the "b/w" histogram doesn't look clipped at all.
Ola
Q-dog
Established
I tried to scan a very overexposed negative but the raw histogram still is all to the left. However the b/w one is to the right. Changing rgb exposure or using automatic settings changes the position of the b/w histogram but doesn´t seem to have any influence on the raw. Is this correct?
/Ola
/Ola
vicmortelmans
Well-known
Hi,
First the distinction between raw and b/w histogram. The raw histogram represents the pixel data as they come from the scanner, so whatever you do *after* scanning, won't have an influence on those. The b/w histogram represents the pixel data in the final, postprocessed image. Both are quite different, for one thing, the raw histogram is for the negative image (thus, low value = shadow, high value = higlight), while the b/w histogram is for the positive image (low value = shadow; high value = highlight).
Some background on the raw histogram. I'm not 100% sure, but I assume that the axis of the histogram shows the (base 2) logarithm of the pixel values. E.g. if you scan 16 bit, the pixel value logarithm will range from 0 to 16.A scanner is a linear device, this means that the amount of light transmitted by the negative has a linear relation to the pixel value. If some pixel A is twice the value of the other pixel B, this means that at that spot, the negative transmitted twice as much light than at the other spot. In logarithmic terms, A-B=1.The density of the negative on it's turn, is linear to the (base 10) logarithm of the transmitted light.
Putting this together, the values on the axis of the histogram are linear to the negative density.
This is useful to explain some behaviours:
- the density range of the negative is not so much an effect of the (film) exposure, but rather of the development, so it doesn't surprise that your overexposed negative doesn't show a different density range
- if you change the scanner exposure, the histogram will not become wider or narrower, but it will shift along the logarithmic axis.
- a negative has a maximum density range of ~2.5 density steps (base 10 logarithm values), which translates into ~8 steps on the histogram axis (2.5 * log(10)/log(2)). That's the maximum width your raw histogram wil ever get. Underdeveloped films have lower density and will have a narrower histogram
So we have two parameters to control the histogram:
1) development will make it wider or narrower
2) scanner exposure will define the position on the histogram axis
What's the optimal tuning?
Let's look at the highlight end of the axis (that's the low pixel values, because we're talking negatives!). There are two quality threaths here.
First there's the scanner noise. Because the scanner is digitizing low light values, the detector noise will have a high impact on the signal.
Second, there's the low 'dynamic range' at this end. Consider a high density gradient area on the film ranging from density D to E, spanning a difference of .3 in density steps. On the logarithmix pixel value axis, this translates into a difference of 1, meaning that pixel value D is twice pixel value of E. If the histogram is positioned to the low end of the pixel data range, values D and E could be e.g. 8 and 4. There's only 4 pixel values inbetween to capture the gradient on the film. If the histogram is shifted 5 steps to high end, values would be 256 and 128. That gives a much smoother gradient!
Conclusion is that the low value area of raw pixel data should be avoided.
This is achieved by
1) avoiding high density range on the film to keep the histogram relativelynarrow
2) targeting at the highest scanner exposure, to 'bump' the histogram as far as possible into the high pixel area, without clipping.
Groeten,
Vic
First the distinction between raw and b/w histogram. The raw histogram represents the pixel data as they come from the scanner, so whatever you do *after* scanning, won't have an influence on those. The b/w histogram represents the pixel data in the final, postprocessed image. Both are quite different, for one thing, the raw histogram is for the negative image (thus, low value = shadow, high value = higlight), while the b/w histogram is for the positive image (low value = shadow; high value = highlight).
Some background on the raw histogram. I'm not 100% sure, but I assume that the axis of the histogram shows the (base 2) logarithm of the pixel values. E.g. if you scan 16 bit, the pixel value logarithm will range from 0 to 16.A scanner is a linear device, this means that the amount of light transmitted by the negative has a linear relation to the pixel value. If some pixel A is twice the value of the other pixel B, this means that at that spot, the negative transmitted twice as much light than at the other spot. In logarithmic terms, A-B=1.The density of the negative on it's turn, is linear to the (base 10) logarithm of the transmitted light.
Putting this together, the values on the axis of the histogram are linear to the negative density.
This is useful to explain some behaviours:
- the density range of the negative is not so much an effect of the (film) exposure, but rather of the development, so it doesn't surprise that your overexposed negative doesn't show a different density range
- if you change the scanner exposure, the histogram will not become wider or narrower, but it will shift along the logarithmic axis.
- a negative has a maximum density range of ~2.5 density steps (base 10 logarithm values), which translates into ~8 steps on the histogram axis (2.5 * log(10)/log(2)). That's the maximum width your raw histogram wil ever get. Underdeveloped films have lower density and will have a narrower histogram
So we have two parameters to control the histogram:
1) development will make it wider or narrower
2) scanner exposure will define the position on the histogram axis
What's the optimal tuning?
Let's look at the highlight end of the axis (that's the low pixel values, because we're talking negatives!). There are two quality threaths here.
First there's the scanner noise. Because the scanner is digitizing low light values, the detector noise will have a high impact on the signal.
Second, there's the low 'dynamic range' at this end. Consider a high density gradient area on the film ranging from density D to E, spanning a difference of .3 in density steps. On the logarithmix pixel value axis, this translates into a difference of 1, meaning that pixel value D is twice pixel value of E. If the histogram is positioned to the low end of the pixel data range, values D and E could be e.g. 8 and 4. There's only 4 pixel values inbetween to capture the gradient on the film. If the histogram is shifted 5 steps to high end, values would be 256 and 128. That gives a much smoother gradient!
Conclusion is that the low value area of raw pixel data should be avoided.
This is achieved by
1) avoiding high density range on the film to keep the histogram relativelynarrow
2) targeting at the highest scanner exposure, to 'bump' the histogram as far as possible into the high pixel area, without clipping.
Groeten,
Vic
Q-dog
Established
Thank you Vic, for your detailed response.
My raw histograms are very narrow, they cover no more than maybe 10% of the x-axis. This is true both for tri-x that I developed myself and professionally developed colour negatives. Maybe I should increase development time to see if I can make the histogram a bit wider?
My main quality concern is that my bw images lacks tonal range. So if I adjust scanner exposure to move the histogram more to the right I might get a better result?
Regards,
Ola
My raw histograms are very narrow, they cover no more than maybe 10% of the x-axis. This is true both for tri-x that I developed myself and professionally developed colour negatives. Maybe I should increase development time to see if I can make the histogram a bit wider?
My main quality concern is that my bw images lacks tonal range. So if I adjust scanner exposure to move the histogram more to the right I might get a better result?
Regards,
Ola
kipkeston
Well-known
Hi. I'm having the exact same problem. I'll be honest, my negatives are good, there are no exposure problems, they were correctly developed and on a lightbox show nice range. They also print just fine at grade 2 or 3. They are tri-x in xtol 1:1.
I normally scan with nikon scan. This produces a nice fat b/w histogram that spans the whole thing. The negative is correctly exposed. The same negative in vuescan gives me a b/w histogram in photoshop that is on the left half of the graph and does not look like vuescan exposed the negative properly. In general I don't find vuescan intuitive and easy to use and the results are certainly not good. I really really want to learn this program because it is supposed to be better.
I normally scan with nikon scan. This produces a nice fat b/w histogram that spans the whole thing. The negative is correctly exposed. The same negative in vuescan gives me a b/w histogram in photoshop that is on the left half of the graph and does not look like vuescan exposed the negative properly. In general I don't find vuescan intuitive and easy to use and the results are certainly not good. I really really want to learn this program because it is supposed to be better.
mfogiel
Veteran
Q-dog
There are a few things that you shoud do:
- make a preview of each negative
- adjust manually the frame, so that no completely black or white border area is in the frame - it may actually be useful to redo the preview after that
- in case of colour, choose the right profile, and if necessary, manually adjust the white balance
- display the histogram at the bottom, and , in case of B&W, try various film profiles, to get the histogram spread across, without the borders going over - with many films the XP2 profile works well, but with silver films I tend to use the Tmax 400/D76 profile at 0.40 density
There are a few things that you shoud do:
- make a preview of each negative
- adjust manually the frame, so that no completely black or white border area is in the frame - it may actually be useful to redo the preview after that
- in case of colour, choose the right profile, and if necessary, manually adjust the white balance
- display the histogram at the bottom, and , in case of B&W, try various film profiles, to get the histogram spread across, without the borders going over - with many films the XP2 profile works well, but with silver films I tend to use the Tmax 400/D76 profile at 0.40 density