No right-click allowed. © Mareike Keicher

The “Solar Curve” (Solarization curve)


What is the “Solar Curve”?

The “Solar Curve” looks like a wave created from the normal linear curve inside of Photoshop. Normally 4 or 6 points are inserted. Mathematically one divides the entire range (0-255) into 5 or 7 parts and sets accordingly the points:

4-point Solar Curve

If you want to set 4 new points, simply divide the 255 (maximum) by five and get 51. These points result accordingly:

Input / Output


It will look like that:

6-point Solar Curve

If you want to set 6 new points, you simply divide the 255 (maximum) by seven and get 36. Accordingly, these points result in:

Input / Output
109/255 * actually 108, has been rounded up
218/0 * actually 217, has been rounded up

It will look like that:

What does the solar curve do with the image?


As you can see in the picture, the Solar Curve is used to map the small contrasts to extreme changes. This creates a very alienated but also enlightening view. This view is ideal for revealing sensor spots/freckles or a single hair, but also to be able better to judge the gentle transitions between light and shadow.

Here it reveals everything that could be somehow “dirty”. So here’s a round of criticism of your own work (from a time when the solar curve was not yet part of my standard workflow):

On the left, you can see a bit of banding; at the top, a sensor spot/freckle was overlooked, and there are still a lot of spots on the forehead. Yeah. Did you see that in the picture above?

Why do you need such precise editing?

This question often pops up (“No one sees that anyway”), and usually, that’s true.
One thing you must not forget: not every screen is the same. Those aspects that your screen may not display could be displayed on another display (possibly a disastrous low-budget discount screen that had been in the public office of the pro-chain smoker association for years and had its best times – if you can speak of it) can look completely different – and indeed by unnatural extreme shifts, such editing errors are no longer almost invisible.

Another example is backlit displays – everything that is printed and then backlit should be very smooth and clean. Mirror foil is also really mean and does not always reveal the best in retouching.

When one works for a client, you never know what he will do with the files – maybe just a brochure is planned, but a bit later could be an exhibition/fair asking for a large format display. You never know.

Working with a visible Solar Curve?

That does not sound tempting?
Immediately seeing where these minimal changes have yet to be made, seeing the little luminance issues burning in the night at Dodge & Burn, that sounds great, doesn’t it?
I use the Solar Curve for sensor spots/freckles, clone stamp, double-check, and hair. To sum up, everything you want to remove 100% clean and has very low contrasts.
Miraculously, you can use this view as a negative or with additional contrast enhancement to unmask even more of the problem areas.

For everything else: Leave it. You run the risk to retouch any naturalness away.

Do you have any suggestions, additions, is this post out of date, or have you found any mistakes? Then we look forward to your comment.
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