To create a new channel that will become your “Lights” channel, drag any one of the RGB channels down to the lower window (it doesn’t matter which - they all have the same data due to the desaturation operation). On the bottom will be a list of any channels you have previously defined. On the top half of this window you’ll see the an entry for each channel in your image (Red, Green, Blue, and Alpha).

Duplicate the Base Layer ¶Įither through the menus, or by Right-Clicking on the base layer in the Layer Dialog: This is easily achieved by duplicating the base layer, and desaturating it using Luminosity as the conversion option. To begin creating the masks we will need to first get a luminosity representation of the image.

Lights (left), Mids (center), and Darks (right) If not (or you just want to brush up), I recommend you read through the Layer Masks tutorial first.įor this tutorial I’ll be using this image by the West Arctic National Parklands: Mountains as Far as the Eye Can See ( cc-by)Īfter going through this tutorial, we will generate channels in GIMP corresponding to these six different luminosity regions in the image:Įxample luminosity masks. This tutorial will assume you are already familiar with layer masks. Need to brighten up the mid-tones in an image without effecting shadows or highlights? Want to split-tone an image with different colors? Need to increase contrast only in the darkest shadows? All of these are trivially easy once you begin considering your image as a collection of tonal ranges. The benefit of using these types of masks is that when targeting tonal ranges the mask itself is self-feathering, helping to avoid problems with blending and hard transitions.īeing able to selectively modify an image based on particular tonal regions can be a very powerful method of editing.

They are derived from the image data itself, and focused on a specific range of tonal values. Luminosity masks are basically layer masks that are built around specific tones in an image.

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