This GIMP (GNU) tutorial demonstrates how to lighten underexposed (too dark) photographs using the Adjustment Curves Editor. To work along, you are welcome to download the Start Image I am working with Here. Unzip the file and open the image onto GIMP’s workspace.
Solorised Sabattier Conversion Using Curves - Intermediate Plus
The Curves Editor is the most sophisticated tool for changing the colour, brightness, contrast or transparency of the active Layer or a Selection. While the Levels Editor allows you to work on Shadows and Highlights, the Curves Editor allows you to work on any tonal range. It works on RGB images.
The Dodge And Burn Tools
Understand The Levels Editor
Darken Images Using Adjustment Curves
Launch GIMP & Organise Its Workspace & Palettes
Repairing photographs is not a precise science. Undoubtedly, you will require considerable patience and lots of time. Additionally, individual photographs have different needs, and require different filters and commands.
An important point to bear in mind is there is no right, or wrong way, of rescuing photographs. My lesson demonstrates the steps I took for my image, and the exact steps may not be appropriate for your image. Therefore, for personal results, it’s important to experiment with GIMP’s photo enhancing filters and commands.
You can quickly Undo a step at any time by pressing Ctrl then Z. Alternatively, click a previous Undo History snapshot - Windows then Dockable Dialogues then click Undo History. In addition, to Zoom in (or Zoom out) of your image; from the top menu choose View then select a Zoom Tool from the subsequent drop-down list.
Open your choice of Start Image onto GIMP’s workspace - File then Open - Ctrl then O.
Duplicate Your Image
It’s important to preserve your original image: therefore, Duplicate your image; Ctrl then D - (Image then Duplicate). Now, close the original image, and work on the Duplicated image.
Ensure the Layers and the Undo History Palettes are visible, and then drag them into position over your workspace - (Windows then Dockable Dialogues - then click Layers and Undo History).
The Adjustment Curves editor is possibly the best way to adjust the brightness of photographs. It affords a sophisticated way of deciding what the impact value of a pixel should be adjusted to, either by adjusting the combined RGB channels together, or by adjusting individual channels. Where brightness control simply adds a number to each pixel, and each channel - without order - the Curves command can for example, increase, or reduce, the values of pixels in a non-linear fashion, and as a consequence, the middle values are adjusted leaving the extremes unaffected. This is how Curves can darken/lighten an image whilst leaving those colours close to solid black, and solid white, unaffected. To do this you click near the midpoint of the diagonal line, as illustrated below-right.
And nudge it upwards to create a curve. Nudging the Point Upwards, lightens images.
However, you can do more than that by creating additional points on the line to change how different ends (of the image) are adjusted - and even combining a change to the combined RGB with individual adjustments to the separate Red Green and Blue channels. While Curves are an excellent combination of power and simplicity, they are not a perfect solution - photographs will always react uniquely; therefore, it is worth experimenting with alternative methods - such as the Brightness and Contrast Filter - top menu, then Colours then Brightness-Contrast.
Tip: Gentle “S Curve”
Most photographs will benefit from the following S curve. To create an S curve, click Two Points over the Diagonal Line, (as illustrated below). Then gently tug the right-side Point upwards, then gently nudge the left-side Point downwards. Don’t be afraid to play with the S curve, and find a contrast that works best with your photograph.
Reset The Adjustment Curve’s Settings
Clicking the following Reset tab returns the Curve to its default (diagonal line) setting.
To lighten your image, from the top menu, choose Colours and then choose Curves. And from the subsequent Curves dialogue box, ensure Channel is set to Value. Then adjust your image’s brightness by left-clicking to place a Point onto the Diagonal Line (Curve) - as illustrated below. Then gently tug the Point upwards. (Tugging the Point subsequently moves the Curve in the Points’ direction).
When you are happy with the amount of brightening, click the OK tab.
Now, from the top menu, choose Filters then choose Enhance and then choose Unsharp Mask. And from the subsequent Unsharp Mask dialogue box, enter the following settings, or experiment, and then click OK.
Congratulations, you have successfully lightened your image using GIMPs Adjustment Curves Editor, and your work is ready to save.
Your image’s brightness and contrast can be further edited by employing GIMP’s Levels Command - Colours then Levels - as demonstrated in my comprehensive Levels Tutorial Here.
Now you are familiar with this technique, you can have lots of fun brightening your favourite underexposed images.
Wendi E. M. Scarth. Top of Page.