Let’s say you have an image with no transparency, and you need one that fades out to a specific color. In this walkthrough that color is black, but the technique works for any target color.
The trick is to stop thinking about selection tools. Instead of lassoing or feathering anything, you let the image’s own brightness drive a layer mask through a custom brush.
Step 1: Build a brush from the image
Make a copy of the image and convert it to grayscale. Play with the levels (Ctrl+L) so the grey areas go whiter — this is where you control how the fade will look. Then define a brush from the result via Edit > Define Brush Preset.
Step 2: Paint the mask
Go back to the original image, add a layer mask, and paint with the brush you just made. The mask hides exactly where you paint, with softness coming from the brush’s grey levels rather than from a feathered selection.
Step 3: Save with alpha
Save as PSD to keep the mask editable, or as PNG for a flattened file. Make sure it’s PNG-24 — GIF and PNG-8 only support 1-bit transparency, which will ruin the smooth fade.
These are the before and after images:
The image “with transparency” (a random background was placed behind it to show the result):
The nice thing about this technique is that you don’t need to lasso or feather anything — every step is a standard procedure. The only thing you must master is the levels adjustment, since that determines the transparency level.
This still works in current Photoshop versions, since layers, masks, and brush presets are core features that haven’t changed. For quick cutouts of subjects, the newer Select Subject and Remove Background commands are faster; but for smooth fades, glows, and gradient-style transparency, the grayscale-brush technique still gives you more control.