negadoctor and module order

Hi all,

I’ve been processing my most recent film scan - Kodak Portra 400 this time. A lot of the scans turned out nicely with very little messing around - sample the film base and adjust Dmax (mine is set quite far from the default - between 0.9 and 1.0 for most of this film… is this normal?)

A couple of shots were taken on an overcast day and the resulting scans look very blue… so I tried the colour calibration module to alter the illuminant. This seemed to work ‘backwards’ - raising the Kelvin value made the whole picture more blue. After some thought I figured that it was operating on the image before negadoctor. Altering the module order made it work in a more intuitive way. I’d think it would be more correct to operate on the positive image rather than the various shades of orange in the negative too.

After doing this I found that doing the same with Exposure and Graduated Density made them work in a more intuitive way too.

Are there any downsides to doing this?

If what I’m doing is correct then why does the default order place negadoctor after these modules?

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Hi there. Film shooter here without a lot of experience using Negadoctor in DT. If you’re adjusting that far and getting a blue cast before color correcting, it’s very possible that you’re either underexposing with your camera or underdeveloping the film itself. (Edit: Since you have some other frames that are well exposed, you’re likely doing something different in-camera on the frames that are not. Portra shouldn’t be overly blue in the shadows). I would start there, making sure you get some good negatives first.

Thanks Rick. Looking at the negs I don’t think these frames look underexposed. It’s my first time shooting Portra but I gather that it likes a lot of light so I erred on the side of more exposure for most of my shots. I’ve been impressed by the extent to which some very bright areas in other shots can be tamed without looking ‘flat’.

If anything one of the ‘blue’ frames is overexposed for the important areas of the subject. The reason for (just) these two frames appearing blue is a bit of a puzzle - it was not the only overcast day on the trip. I can only guess that it was a combination of the sky conditions and the fact that we were on top of a hill.

TBH these two frames are never going to be great works of art but it did prompt me to go poking around with the module order while trying to figure out how to make them look more natural.

I was thinking some more about the Dmax adjustment and I now think that part of my original post may be a red herring sorry. The scan software is adjusting the levels for each frame so the Dmax is probably only re-adjusting the previous adjustment. My software won’t do any kind of raw for negative scans sadly.

Note that you can upload large files, even raw images, to this forum. If you have something that can be shared (not objectionable to viewers and subjects), please attach an example.

Thanks. Nothing objectionable but pictures of people which I’d rather not post here.

I have used negadoctor module on a lot of scans. You MUST alter the module order as the negadoctor has to invert the image early in the pipeline. So I agree with your approach.


I dont think you have to alter the module order. However there are modules that you need to disable. Certainly filmic, and maybe even exposure. Negadoctor can deal with all kinds of color casts

There is also a youtube video by the dev aurelien

I’m agree with @Terry. I’ve used negadoctor with black and white film but at least with Darktable 3.8 it’s better to alter the module order. As far as I understand, you have to use Negadoctor in the same level as the base curve. After using it, you can process as display referred.

I think that by default it is located over tone equalizer. If you put negadoctor under tone equalizer, you can use it intuitivelly. if you don’t do that, you have to use it in the opposite way.

I will try to do some test in the afternoon to confirm this.

It’s quite simple right? Modules in the pipe before negadocter are altering the negative scan, and the inversion process has yet to happen. So all kinds of things like color balance there will alter the film base, so will at least require making changes to negadocter again.

The workflow is quite sane how the topic starter explained: You load the file up, you apply negadocter to get an inversion you can work with. From there one, you probably want to do more to the file, so you need to add modules / filters ‘on top’. So that means placing them behind the negadocter module.

I often scan and convert an entire roll of 35mm together. That means I have a tiff file with all the negative scans glued together, as one big mosaic. That’s what I load into Darktable to load negadocter. I then try to get a good conversion, which looks as good as possible for the entire roll.

Then, I load the individual files and I use the selective copy/selective paste to copy the negadocter settings into all those file at once.

But yes, then the editing starts. Some files I want to raise the exposure of, or to mess with contrast, or to make them slightly warmer or colder. So each negative scan is from that moment one like a ‘raw photo’ file for me. I make edits as I see fit. And yes, this sometimes even includes filmic to handle loads of dynamic range in a picture :). And most of them get some exposure and color calibration and/or color balance added to them. All need to be placed after negadocter in the module order.

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Thanks all for the comments. To address a few (in no particular order)…

For black and white I generally just do things the old (display referred) way and play with the sliders in Levels until it looks nice.

My scan produces a 24 bit TIFF (with levels adjusted by the scan software). DT does not include Filmic RGB in the TIFF pipeline by default. I don’t think I’ve ever used it on a negative scan but I have added it once or twice for some Kodachrome scans.

In the past I’ve done the adjustments for colour neg scans by sticking to Colour Balance RGB and doing the exposure adjustments ‘backwards’. This time I specifically wanted to mess with the illuminant which is what prompted me to change the module order.

I have watched Aurelien’s video on Negadoctor (twice IIRC). I don’t recall him addressing this question but it has been a while since I watched it.