VueScan Exposure Lock Underexposed

Flatbed and Film Scanners Vuescan
1

I’m following the “VueScan Lock Exposure” advanced guide with C41 color negative film. Scanner is Primefilm XA. Every time I attempt to have NLP or VueScan invert the image, it comes out underexposed.
The steps:

  1. Preview
  2. Crop unexposed part of film
  3. Preview Again
  4. Lock Exposure ON
  5. Preview Again
  6. Save RAW DNG following NLP instructions
  • Am I supposed to change the individual color gains to overlap each other on the image histogram to the right side (maximum exposure given the unexposed part of the film)?
  • I don’t see a difference with what lock exposure does.
  • Could this be due to not setting the scanning exposure correctly?

Here are 3 screenshots, lock exposure OFF and neutral gain, lock exposure OFF and gain adjusted to overlap, and lock exposure ON and gain adjusted to overlap.

Which (if any) is the correct-looking scan for C41 uninverted film?

I tried to email Hamrick but he said he could not help with this type of question and that I should “hire a consultant and pay him a few thousand dollars to provide this kind of technical support”. Any help is appreciated!

2

I’ve only digitised negatives with a DSLR or an Imacon scanner (have only used VueScan to scan positives) so I can’t say anything very useful. This thread may help until someone more knowledgeable comes along.
https://forums.negativelabpro.com/t/understanding-the-lock-exposure-setting-in-vuescan/4246

The main thing in most negative scanning is to set the exposure so the histogram shows the film base near the right edge but with no clipping.

3

Hmm, I guess my question would be if the individual colors should overlap each other on the right edge, or should I keep the spacing as it should with only the red touching the right edge?

4

I’d leave it as it is so as not to alter the colour balance of the negative.

5

Vuescan, like SilverFast, is supposed to provide for its own controllable exposure and negative reversal algorithms, so what’s the point of using NLP altogether if you are already using one of those other applications? However, if you are using those applications only to drive the scanner and digitize the negative to produce a raw digital negative, I don’t see the point of locking exposure in the usual case when different photos require different exposure to prevent highlight clipping or under-exposure in any one of them. I would expose each negative such that the image data is all contained within the histogram without climbing the walls on either side, then use NLP for roll analysis on all the digitized, still negative images.

2 Likes
6

I had Roll Analysis reject to use the images of rolls because their exposure was too different. Therefore, and for camera scanning, individual exposures can disable RA. Whether that is the case with scanner scanned images, I cannot say, but there might be something in here:

7

Where are you getting step #2? That is not correct.

If you are cropping into just the unexposed part of the film (i.e. only showing the border itself in the crop) this will cause the exposure lock to miscalculate.

You want the entire film frame in view when you lock the exposure.

Alternatively, you can hit “lock exposure” and then manually set the “gain” to 1.0. This will make sure that Vuescan doesn’t alter then gain in between frames (which will cause issues with Roll Analysis).

8

Where are you getting step #2? That is not correct.

I was following the VueScan Lock Exposure Guide after reading the NLP Guide about locking exposure. After running some tests, I couldn’t see a difference between selecting ONLY the film border or the whole image, as the exposure always chose to lock to around 3.07 gain, just before the red started clipping.

After the negative conversion, I can see black clipping and very little dynamic range in the 3.07 gain version compared to the one set to 1. I think what threw me off is the uninverted image looks extremely pale and not orange whatsoever, I assumed it should look at least a little orange like the film itself and the link to your comment below. I will use gain 1 going forward.

Is my understanding correct in that “Lock Exposure” sets the highest gain possible without clipping? Is the unexposed portion of the film considered pure white? Or is there more going on?

Is the current recommendation to still use “Color Negative” media mode as suggested here? That is giving me a much bigger difference.

9

It really just depends…

The biggest goals during scanning in Vuescan are simply:

  1. Don’t clip any highlights or shadows
  2. Use the same “gain” values for all the scans in your batch (to avoid creating inconsistencies during conversion)

For this, locking to “Gain: 1” is usually sufficient (unless you are seeing clipping in the shadows with Gain:1, in which case you could bump it up a bit).

Rarely, some scanning models (like Nikon Coolscan) actually offer analog gain controller, with independent control of the gain for red, green and blue

In theory, this could improve the data being captured. But the tradeoff is that it could lead to inconsistency during post-processing.