Scanning a C41 negative

Most scanning software will allow you to do all of this using “auto” settings, but that is quite boring and I prefer to do things “manually” as it gives a greater level of control over the final result.

The first step is to scan the negative.

Most people will select “scan as a negative” as that is logical, but I’m going to select “scan as a slide” as this means the scanner will not make any atempt to adjust the colours and I will do all the colour correction in GIMP instead.

Here is a screenshot of the scan window, and the result is basically very orange, as a negative has a “mask” which causes it to be so orange.   It’s something to do with the dyes being “impure” and the orange mask has annoyed me till I figured out how to correct the colours!

scanning window

I have got my scanner software set up to import the image into GIMP directly, as this is simpler than having to save as a tiff first.

The next stage is to “invert” the colours in gimp to give this:

inverted

It is of course very blue, and this is the result of that annoying orange mask, as orange inverts to blue!

What we now need to do is to “tweak” the levels of each colour channel.
For each channel (red, green and blue) we are going to make 3 adjustments:
1) Black Point
2) White Point
3) Grey Point

The black and white points are done by looking at the histogram, as it’s obvious that the picture information is contained in a fairly narrow part of the colour channel, so lets move the settings so that the black and white points are where the picture data is:

First the red channel:
red channel

Then the green channel:
green channel

And finally the blue channel:
blue channel

Remember that you want to set the black and white points for all 3 channels FIRST and only when you have done this should you adjust each grey point.

The reason is that adjusting a grey point is a “fine” adjustment so you don’t even want to think about adjusting grey points till you have set the black & white points.

The final setting of grey points is where the “artistic” part comes in as you are tweaking the final look and “mood” of the image at this stage.

OK I have set black, white and finally grey points and this is what I get:

levels adjusted

Gone are those nasty colour casts, and the image looks quite “normal” in fact.

Remember this can all be done automatically so if you have loads of pictures to process then auto is the way to go, but it’s sometimes nice to know what the software is doing “under the hood” by doing everything manually.

Here is a link to the final picture as posted on flickr.com

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