Scanning C41

This is a quick instruction on how to scan C41 (colour negative) film and obtain vibrant, accurate colour instead of the washed-out faded crap that you normally see people posting.

The Importance of the Black Point

What most people get wrong is the black point and for two reasons:

Therefore a simple auto-levels approach or setting the black point to the base colour will result in too-low contrast and (depending on the film) colour casts in the shadows.

The most important part of this process is choosing the black and white points appropriately.


Scanning a roll of film requires the following steps:

  1. previewing the first frame and choosing the scan-exposure
  2. re-previewing with the proper exposure and choosing an approximate black-point
  3. scanning at full resolution
  4. choosing the RIGHT black-point
  5. saving your files

The process is demonstrated below with Vuescan, a Nikon 8000 and some 6x7 Portra 400 which is meant to have good skin-tones. Lighting is from a Bowens monolight through a softbox, so it should be pretty neutral - we're not trying to fix any crazy casts or mixed light here. You should be able to use the same process with any decent image editing software that gives you curves control on each of the R, G and B channels separately.

First Preview

Load the film in your scanner with some of the clear rebate visible.

First, you set Vuescan to 64-bit RGBA, "Light" IR clean (assuming your scanner has ICE), low resolution (about 150dpi) and auto-exposure (no Lock Exposure). Make sure you're in Advanced mode or whatever it is where all the options and histograms are visible.

Perform a Preview and you'll probably get something that looks horrible:

Now, select your image and the background clear film (mostly-black looking) and press "Lock Exposure". In my case, it suggested 1.912 so I'm going to go with 1.8 to make sure I don't over-expose the shadows in the scanner. Type the chosen exposure (1.8 in my case) into the "RGB exposure" field and press Preview again. You'll get a slightly different image, still horrible:

This is better than it often comes out. Next, select the deepest darkest part of the clear film base; the Preview window will go to crazy-contrast because there is almost no dynamic range in the film rebate. Select just the darkest part you can and then push the Lock Film Base Colour checkbox:

Now, select only the image and select the Lock Image Color checkbox. Press Ctrl-2 to show the black/white point histogram.

Note the presence of three separate R, G and B sliders for both the black and white-point. Now, we need to think about what is wrong with this image:

First step is make a stab at the gamma. In Vuescan, this is tweaked most easily with the Brightness slider; moving the slider down has the following effects:

It's equivalent to imposing a concave/up-swept curve in Value, if you're using a program with explicit curve control. I'm going to shove it down to about 0.65 instead of 1.0, giving the following:

Now the casts are really obvious. We need to take lots of red and a bit of blue out of the shadows - see the top of the head. Start dragging the black-point sliders around:

Now the darker areas (top of head, wooden background at top-right) are starting to look about right. The highlights are still way too cold though, so now it's time to adjust the white-point sliders. Note that when you mouseover an image region, Vuescan will tell you the 8-bit RGB output value you're hovering over. If there's white cloth or similar in a scene, this is a really good way to aim for neutrality. Here I'm using the mittens.

Next, do the full-resolution scan and make final adjustments to that. Making adjustments at this stage is a slower because there are a lot more pixels, especially if you're doing large format; you want to be making only very fine adjustments now.

I decided that the saturation was too high here so I've increased the brightness to 0.75. Also took a bit of green out of the shadows after inspecting the RGB values in the shadow under the legs and noticing that the cushions were way too fluorescent looking. The final result is this, which I think looks reasonably accurate:

The head is a bit red at the top but I suspect that's due to the dark-red couch just a foot away rather than a conversion error.

Finally, enter the basic EXIF info and save the scan. I keep a DNG and a JPG; if I don't like the colouring at a later date, I can reopen the DNG in Vuescan and do the tweaking again from the original 16-bit data.


Once you've scanned and converted the first frame, most of the settings are re-usable for the whole roll, or several if they're the same film. Different lighting will call for a different white-point, but the black-point should be fairly consistent unless you want to change contrast.

Leave the two Lock checkboxes in the Input tab selected, don't change the RGB exposure. Put your new film in and press Preview; you should get a pretty good-looking image. Crop and scan it, then do your final adjustments and save - all of the remaining images on the roll should require minimal further adjustment unless the lighting changed dramatically.

Here's my next frame, no further adjustment:

Pity about the catchlight placement but I can't blame the scanner for that...

You might discover a bad shadow tint in a later frame that wasn't obvious while processing the earlier ones - by all means go back to your saved DNG files and re-tweak them.

Alternative Adjustment

In Vuescan, "Film base colour" defines the left end of the histogram. Therefore if you don't want to manually adjust three sliders you can instead manually change the Film Base Color values in the Color tab. Changing those shifts the curves up or down wholesale so with a bit of care, you can arrange it so that all of the black-point sliders would be at the far-left.

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