Using the RGB Tone Curve

Using the RGB Tone Curve

This post was updated on July 27th, 2019

Adobe ® Lightroom’s Develop Module explained

In the previous article of this series, we examined the Tone Curve Panel. This post shows different ways of using the possibilities that the RGB Tone Curve offers. The next article of this series will have a look into how to use the separate color curves.

Tasks to be explained

Tasks for the RGB curve:

  • Fine tuning of contrast and brightness.
  • Transforming a negative into a positive
  • Creating a matte look

Tasks for the separate color curves

  • Fine tune the color balance
  • Create a cross-processed look

Working with the RGB Tone Curve

Fine tuning of contrast and brightness

Fine tuning the contrast or brightness of a photo means adjusting the RGB tone curve. You can do this either directly by setting points onto the graph and dragging them up/down, or by using the sliders, or by a combination of both. Changes made to the RGB tone curve affect mostly the mid-tones and less the darks and highlights, which helps to avoid clipping.

In the following examples, I adjust the brightness by changing the tone curve directly, before I change the contrast of a second image using the sliders instead. Of course, you can use either method for both. Notice how, in none of the examples, the histogram indicates any black or white clipping after I applied the changes to the tone curve.

Adjusting the brightness

Moving the tone curve upwards adds brightness to an image.

Brightening RGB Tone Curve
Tone Curve – brightening the photo
Original Linear RGB Tone Curve - This post shows different ways of using the possibilities that the RGB Tone Curve offers. The next one shows how to use the separate color curves.
Prohodna Cave – Original
Tone curve adjustments applied to brighten image - This post shows different ways of using the possibilities that the RGB Tone Curve offers. The next one shows how to use the separate color curves.
Prohodna Cave – Brightened

Moving it downward darkens it:

Darkening Tone Curve graph
Darkening Tone Curve
Kirkjufell with a darkening tone curve applied - This post shows different ways of using the possibilities that the RGB Tone Curve offers. The next one shows how to use the separate color curves.
Kirkjufell – with darkening Tone Curve

Fine tuning contrast

To add contrast to an image drag the curve in the left half a little downwards and in the right half a little upward, to form an S-curve. If you were to achieve this with the help of the sliders, you would drag the highlights slider a little to the right and the shadows slider a little to the left.
The resulting S-curve increases darkness in the darker areas and brightness in the brighter ones.

RGB tone curve to enhance contrast
S-Curve in the Tone Curve Panel to adjust the contrast

This post shows different ways of using the possibilities that the RGB Tone Curve offers. The next one shows how to use the separate color curves.
Beklemento Freedom Arch – Original
RGB Tone curve changed into an S-shape to increase contrast - This post shows different ways of using the possibilities that the RGB Tone Curve offers. The next one shows how to use the separate color curves.
Beklemento Freedom Arch with S-curved Tone Curve applied

If you create an inverted S-curve (also called Z-curve) by dragging the right half of the curve down and the left half upward, you decrease the contrast. This, however, is not a feature that is used very often. 

Transforming a Negative into a Positive

Imagine you borrowed a professional Negative Scanner to scan all your good old analog photographs. By some mistake, you scanned them as Negatives and did not convert them directly into Positives before returning the Scanner.
Instead of cursing and dipping into the expenses again, you could easily convert your Negatives into Positives with the help of the Tone Curve – granted that you scanned them in a high enough resolution they’d even be printable in larger sizes.

Quick tip: 
For a full resolution scan your Negatives at 7200dpi. However, be aware that the resulting files are huge, so you might want to get another external hard drive.

To convert a Negative into a Positive, or vice versa, drag the Black Point of the Linear curve all the way up into the left upper corner and the White Point all the way down into the right lower corner of the Tone Curve. That’s it.

Below you see an old Negative that I scanned (not on the full resolution) as a Positive for the purpose of this article.

Negative of Rubjerg Knude Fyr - This post shows different ways of using the possibilities that the RGB Tone Curve offers. The next one shows how to use the separate color curves.
Rubjerg Knude Fyr, Denmark – Negative scanned as Positive

Since I rather would like to see the positive, I adjusted the RGB Tone Curve as follows.

RGB Tone Curve for Negative to Positive conversion
Conversion RGB Tone Curve

And, after adjustments to the Black and White slider in the Basic Panel, the result looks as follows.

Negative converted into a Positive - This post shows different ways of using the possibilities that the RGB Tone Curve offers. The next one shows how to use the separate color curves.
Rubjerg Knude Fyr, converted Negative

Of course, you would make some more adjustments to turn this into the same type of photo that your analog camera once captured. These additional adjustments, however, are out of the scope of this blog post.

Adjusting the contrast in a conversion Tone Curve

If you now also wanted to change the contrast a little bit, remember to drag the upper left part toward the left to increase brightness and the lower right part toward the right to increase the darkness. Alternatively, if that is easier to remember: make some adjustments for the contrast before you convert your Negative into a Positive.

Using this feature on a Positive

If you were starting with a Positive instead of a Negative, you would convert the Positive into a Negative. Besides artistic expression, however,  I haven’t found a reason to do so.

Creating a Matte Look with the RGB Tone Curve

To create a matte effect, we are brightening the Shadows and are adding a bit of haze to the following image.

This post shows different ways of using the possibilities that the RGB Tone Curve offers. The next one shows how to use the separate color curves.
Alexander Nevsky Cathedral, Sofia, Bulgaria – original

Open the Point Curve in the Tone Curve Panel, make sure that the Channel is RGB, and add new anchor points onto the diagonal line by clicking on the linear graph at 1/4, 1/2 and 3/4 up the curve. Then add a last a little before the first one. 

RGB Tone curve with anchor points
Tone Curve with the first additional anchor points

Now move the Black Point on the left vertical axis up, but keep it within the first quadrant to not overdo the effect.
Notice that your curve is only changed between the Black Point and the 1/4 point, however not beyond that. So the three points we added initially work as anchor-points to keep the curve in those areas as it is.

RGB Tone Curve for Matte Look
Tone Curve for Matte Look

The result looks like this:

This post shows different ways of using the possibilities that the RGB Tone Curve offers. The next one shows how to use the separate color curves. data-pin-media=
Alexander Nevsky Cathedral, Sofia, Bulgaria – Matte Look



All trademarks and copyrighted items mentioned are the property of their respective owners.

I am in no way affiliated with any of the products used in this post-processing process. I do not receive any kind of compensation for this article, it was neither offered or asked for.

THIS BLOG ARTICLE “Using the RGB Tone Curve” IS NOT AUTHORIZED, ENDORSED OR SPONSORED BY ADOBE SYSTEMS INCORPORATED, PUBLISHER OF ADOBE ® LIGHTROOM

All photos taken by Lille Ulven Photography.

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