A channel is a raster image, containing one value per each pixel. A single channel is often rendered as a grayscale image (small values as blacks, large values as whites).
A color image consists of four channels: values of Red, of Green and of Blue and transparency values. A raster mask can also be viewed as a channel. In addition, Photopea lets you create your own, independent channels.
You can work with channels in the Channels window (press Window - Channels). The list contains the Red, Green and Blue channels of the image, masks of a current layer, and independent channels.
You can hide or unhide each channel with the eye icon. When only one channel is enabled, it is rendered as a grayscale image. When multiple channels are enabled, non-RGB channels are rendered as a "red mask" (black as red, white as transparent) over the RGB image.
A useful feature in the Layers panel:
- Alt+click a layer mask to enable it and turn off other channels ("grayscale view")
- Alt+Shift+click a layer mask to enable it together with other channels ("red mask view")
The Quick Mask Mode simply turns a selection into an independent channel, that is enabled toghether with color channels.
Working with channels
Click any channel to select it. All editing (e.g. painting, adjustments, filters ...) will be applied only to that channel (e.g. a blue channel of a current layer, a raster mask, or an independent channel).
Icons at the bottom allow you to turn a current channel into a selection, create an independent channel from a current selection. You can also create an empty channel (all black), or delete a current channel. You can double-click the name of an independent channel to rename it.