Non-Destructive GIMP Levels

GIMP's "Levels" command lets you change your picture's contrast, as well as its range of light and dark tones. Imaging professionals call such changes "destructive" because they permanently change your original picture. That means your picture's original imagery is potentially lost forever, unless you make a duplicate of the image. By contrast, Photoshop and other imaging programs provide "adjustment layers," which let you change the contrast without affecting the image. GIMP offers alternative commands that perform many of the same functions as "Levels," all without changing your picture.

1. Make Duplicate Layers

   • One of the simplest solutions to the problem of destructive level editing is to create a new layer on which you change levels. This solution protects the original layer, while only altering the duplicate. To try this approach, right click the thumbnail in the "Layers" panel that shows the image you want to adjust. Select the "Duplicate" command from the pop-up menu, then run the "Color" menu's "Levels" command as you usually would. Your changes only impact the duplicate layer.

   Layer Mode "Screen"

   • If you've been using the "Levels" command to lighten your images, try using the "Screen" layer mode instead. Right click the "Layers" panel item that holds your image, then select "Duplicate" to make a copy. Click the "Screen" item from the drop-down list on the "Layers" panel to lighten the image.

   Soft Light Mode

   • If you need to darken or lighten your image, you don't need to use "Levels." Try a new layer with the mode set to "Soft light" to darken or lighten. To darken, for example, first create a new layer by clicking the page icon on the "Layers" panel. Select "Soft light" from the drop-down list at the top of the panel, then fill the layer with black by selecting the "Edit" menu's "Fill with foreground color" command. The "Soft light" mode makes the normally opaque black layer semi-transparent, allowing you to see the original image. To lighten instead of darken the image, click "Fill with background color."

   Layer Masks

   • One workaround for GIMP's "Levels" command is to paint onto layer masks laid over your original image. Layer masks hide certain portions of an image and reveal others. Painting white onto the mask reveals the masked layer and hides underlying layers, while painting black onto the mask hides the layer and reveals underlying layers. Painting gray on the mask lets part of the layer show through, while also partially revealing underlying layers. This behavior allows you to lighten just the portions you want by first placing a white background layer under your image. Paint those areas of the mask that cover the portions you want to lighten with a darker shade of gray than surrounding portions. The darker parts of the mask reveal more of the underlying white layer, which brightens the portions directly under the darker mask parts. To begin experimenting with layer masks, right click the "Layers" panel item that shows your image's thumbnail, then select "Add layer mask." Click the paintbrush icon from the "Tools" panel to enter painting mode, then paint onto the mask. The lighter the color you use, the more clearly you'll see the underlying image.