hi,
I am playing around with the module Negadoctor. However, trying to convert black and white negatives to positives, I keep getting a monochome photo with a color color cast (usually green or purple), no matter how I do it. The only workaround I found is activating color balance rgb and setting chroma to -100%.
What is going on here?
Thanks in advance
Anna
I think for many people it will be hard to give good advice without seeing the image and/or what you did. Maybe you consider sharing a RAW file and you will surely get some edits you can have a look at.
I use the colour balnace rgb for BW conversion after the negadoctor module, this does the trick 
this is also the only way I found to get decent results…
Negadoctor is trying to compensate for the color of the film base, which you need for color, but not b/w.
I’ve also seen this effect when setting negadoctor to black and white mode… I guess the issue is something different, maybe demosaicing?
@betazoid sorry a correction, I’m using the color calibration module for bw conversion!
how?
By just using the BW Delta 100 preset of color calbration. this goes before negadoctor (which is default anyway)
In essence I have the modules:
That does the trick
Edit:
For reference I added an image (CC-BY-SA) Ilford Delta 400 taken with Flexaret VI, developed in Moersch Eco Film Developer + the sidecar file
DSCF7194.RAF.xmp (7,0 KB)
DSCF7194.RAF (29,0 MB)
The Luminance-based preset seems to be suitable for all films that are not in the preset list, doesn’t it?
The preset is just a minor difference, You could just set the channels within the color calibration modules gray tab all to 1/3 and will get a “neutral” effect. But this will not change anything as the image is black and white to begin with.
I’m just using the preset because I’m lazy and it is faster to select.
Hi,
going back to this thread, I’m inverting a camera scanned Fomapan 100 film (black and white).
Can someone explain to me why Negadoctor gives me a color cast even selecting “black and white film” in the film stock?
If I use “color film” the result is more neutral. Why is this possible?
Possibly because the camera you used to “scan” is shooting in color.
And thus things like white balance have an influence. Unless you used a D65 light source?
The film stock selection does just that: correct for different film types…
The light was a 6000k Led.
I thought that selecting “colour of the film base” was ruling out the white balance thing. Basically if I want an actual black and white picture I have to use the “monochrome” tool too, right? Shouldn’t this be automatic when selecting “black and white film” in Negadoctor?
Check out this post: Darktable, Negadoctor, and Black and White Flatbed Scans: A workflow demonstration and watch his video where he has to manipulate the colors (I ask him about converting it to monochrome instead in that post).
He uses a flatbed scanner, and saves the images as color TIFFs, I believe. Which, I believe, would have the same results when brought into darktable as you shooting a b&w negative with a color camera and bringing it into darktable: it’s technically a color image you are dealing with, so yes, I believe, it needs to become monochrome at some point in the darktable workflow.
No, as once you have removed the base mask, the density values from each of your camera or scanner colour channels needs to be linerized.
Those colour corrections are compensating for the sensor’s filters not being equally sensitive and the film base mask also filtering out some light.
So, no, it should not be automatic.
You can slap a monochrome module on it, if you like it and call it a day. As I’ve said elsewhere, it’s art.
Furthermore, black and white prints are not strictly speaking monochrome. There is a long history of toning prints (sepia, selenium, platinum) to change the tonality of a print.
You can emulate that some what with the colour corrections in negadoctor.
Ok thanks, it’s clear now.
