Scanning negatives, part 2 – Post Processing

In the previous part I assembled a DIY film scanner that allows me to scan a whole roll of film in less than 2 minutes.
In this part we will create process in Photo Reactor to turn old negatives into a great looking picture.

The task is to create a process that will be mostly automatic and can be used in a batch processing. Of course it would be ideal if we can just invert the whole image – but sadly that is not the case with film. If you just invert the captured negative, the result will be most likely a weak low contrast image with a strong color cast.

A first idea would be to start adjusting contrast of the whole image as it is, but a lack of general contrast is not the problem here.

In color films each emulsion layer has different dynamic characteristics (that also change with time) and so each emulsion layer of color film captures the light in its very own dynamic range quite independent from the rest.

So to do this right we need to split the image into its components and adjust each component separately.

Inverting negative is definitely not enough

But first thing first. The film has two sides – the mate emulsion layer and the glossy back layer. The emulsion layer faces the lens and so when we capture the negative we should also place the film so the mate side faces the lens.

This means the sides will be flipped in the final image.

So first we will Horizontally flip the image, then invert its colors.

The next step is the automatic color correction. What we do is to split the inverted image using Channel Split into R,G and B components and process them separately.

Each RGB component will have Histogram Auto-Stretch with low shadow and highlight tolerance (around 0.8). This will find the left and right histogram range of each component and stretch to the full dynamic range. Depending on the age of the film and its characteristic there may be a bias towards different color so a levels were added after each step. The only thing we are interested in the levels is adjusting the gamma so I exported the gamma slider as logarithmic knob. The next step is to use channel merge to put it back together.

At this moment the result already starts to look good – but maybe too good.

The saturation is really cranked up. To bring it to more realistic levels we will add Hue/Saturation block and bring the saturation down to about -20 to -30

The last parts are more like a house cleaning. I added film simulation but turned it all the way down. I can use few film presets to spice up the image. (Agfa Vista 200 preset seems to work well with strength about 15). Then added unsharp mask with a large radius and small amount to give it a more 3D look. And that’s it.

Now we have a reasonably good automatic image processing that can be fine tuned and used in batch processing.

To download the whole process:

You need to unzip-it first, then load in Photo Reactor.

In a future article we will look into dust and scratches removal.

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