How to Invert Colour Film Negatives in Photoshop
Using Replicable Equalization Technique7 min read by
This guide will demonstrate and explain a simple, reliable method for making high-quality positives from scanned colour film negatives.
You don’t need any software or plugins other than a copy of Adobe Photoshop.
✪ Note: The link above has a few special offers on Adobe plans and products. Last time I checked, you can get the “photography” package for $10/mo.
There are three steps. The first two list the precise instructions for obtaining an optimal amount of visual data to create an equalized positive. The final step is colour correction.
Prep: Tools and media.
In the example below, I am using Adobe Photoshop 2021. However, this method is transferrable to other image processing software, like Lightroom, Gimp, ImageMagick, etc.
This method will work with RAW files, TIFFs, JPEGs or any file types, sizes, and qualities. For best results, I recommend using high bit-depth images.
Download my sample film scan off PrimeFilm XA to follow along as I edit it below:
➜ Free Download: Sample uncompressed 48-bit 35mm Film Scan (TIFF)
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1. Invert the image (Negate) — 5sec.
Let’s begin with the simplest and most straightforward step in this process. Load up your negative scan into Photoshop and create a new Invert adjustment layer (fig. 1 — A).
✪ Note 1: Creating a layer on top of your scanned negative, as opposed to editing the image layer itself, ensures that there’s minimal loss of quality in your final image. This technique is called non-destructive editing.
✪ Note 2: You will need to use a different technique to invert colours if you use Lightroom or Camera RAW.
At this point, you will likely notice a strong blue cast on top of your image. This effect will depend to various degrees on your exposure, film type, and scanning device type. Essentially, you’re seeing the film’s orange mask, but it is now the opposite of orange — blue. We will work on fixing that next.
2. Remove noise (Equalize) — 25sec.
Time to create a usable image out of your scan: an equalized positive.
Create a new Curves adjustment layer (fig. 2 — A), and select the Blue colour channel (fig 2. — B). Have a look at its histogram (fig. 2 — C).
In my image, the histogram for the Blue colour channel shows empty spaces to the left and the right (fig. 2 — C). We need to equalize our distribution of blue tones to ensure that the fringe tones of our scan align with the min/max of the channel space. The same should also be done to Red and Green colour channels.
To equalize the distribution of the individual Red, Green, and Blue channels’ tones in your image, drag the handles underneath the Curves to align with the outer fringes of the histograms (fig. 3 — A). Then, switch to the next colour channel and repeat (fig 2. — B → fig. 3 — B, C):
This completes the essential, repeatable part of inverting colour film negatives in Photoshop. For some scans, this is enough, but in some cases, you may still have a blue cast or unnatural colours in your image. We will work on fixing that next.
✪ Note 3: You can use Photoshop’s Levels adjustment layer to equalize your colour channels the same way you did with Curves.
✪ Note 4: See the histogram equalization caveats, below, for when your scan has a border or images of certain qualities.
3. Colour correct.
Your colour correction objectives and tools may differ from mine. Or you may decide that your image looks as good as it needs to be — in which case, you are done.
To further improve your scan, you can try my approach (below) to reduce the blue cast and ensure that the colours match the scene. This step is much less defined than the precise actions described in one and two and is open to interpretation and experimentation:
Create a new Color Balance adjustment layer (fig. 4 — A), and work through the Shadows, Midtones, and Highlights (fig. 4 — B) until the colours in your image begin to match your memory of the scene’s actual appearance:
Because you’ll be working with arbitrary values, this step will require some getting used to. The tool that I use here, the Color Balance adjustment layer, is particularly suited for this operation as it lets you adjust the colours without changing the contrast.
Automatic colour balance may also be set using sample pipettes in either new Curves or Levels adjustment layers (fig. 5) and clicking the black, grey, and white points in your image. Though it may not always work as intended.
If you need to have a way to quickly and accurately adjust the colour balance in your shots, consider taking a shot of a colour calibration chart in the same light as your actual photo. You can then use the automatic colour balance technique with colours picked from the chart with greater confidence that they are accurate. Although, this method may not be practical for your photography.
Colour-correcting specialty film, like Lomography’s Lomochrome Purple or redscale film will be covered in a separate article.
Histogram equalization caveats.
If your scan has a film border, but your exposure’s black point isn’t as dark as the unexposed piece of emulsion, your histogram will lie to you. This could happen when your frame is overexposed. To prevent this from throwing you off, I recommend using the crop tool to trim the edges before starting work on your histograms. If you still desire the border, you can use the crop tool to expand your image back after you’re done.
⚠️ Warning: Histogram equalization may cause issues in images with ambiguous white/black points. An example of such a photograph is deep sunset when the brightest part of your sky is yellow (not white); histogram equalization will attempt to turn that colour white.
Notes for Adobe Lightroom.
Adobe Lightroom and Adobe Camera raw do not have a tool to invert image colours. Instead, you can achieve the same effect by moving the bottom-left point of your colour channel (A) curve up and the top-right point of your colour channel (B) down.
Do this while simultaneously moving those points to your histogram’s left and right edges.
For further colour correction, I found the Color Grading tool helpful. However, you can also change your colour balance by altering the shapes of your Curves or via any other Lightroom tool you’re comfortable with.
For impeccable results, I recommend doing further research on colour correction as it’s beyond the scope of this article.
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