Today’s Question: Is there any way to paint in transparency on part of an image in Photoshop?
Tim’s Quick Answer: Yes, sort of. Transparency in an image really means that pixels have been erased (or partially erased). To streamline the overall process with a non-destructive workflow, I recommend “bundling” all layers for the image into a new layer group, and then using a layer mask with that layer group to paint transparency where it is wanted in the overall image.
More Detail: Many photographers choose to employ transparency in an image for a variety of reasons. For example, including transparency around a key subject in a photo can enable you to place the resulting image on a web page or in certain documents, so that the background color or texture appears in the transparent areas.
If you are printing it is probably easier to simply add white in the areas where you would otherwise want transparency, since white won’t actually be printed and thus produces the same effect as transparency would.
In some cases adding transparency can be very simple. But since there are a number of variables related to how many layers you might have as well as the type of layers involved, I recommend an approach employing a layer group that will work under virtually all circumstances.
To get started, you’ll want to be sure that the Background image layer has been converted to a “normal” layer. To do so, simply double-click the thumbnail for the Background image layer on the Layers panel and click OK in the New Layer dialog that appears.
Next, select all of the layers on the layers panel by clicking on the bottom-most layer (the layer that had been the Background image layer) and then hold the Shift key on the keyboard while clicking on the top-most layer on the Layers panel. Then click the panel popup menu at the top-right of the Layers panel and choose “New Group from Layers” from the popup menu. This will create a new layer group that contains all of your existing layers.
At this point you can add a layer mask to the layer group by clicking the “Add Layer mask” button (the circle inside of a rectangle icon) at the bottom of the Layers panel. You can then use the Brush tool to paint with black on the layer mask in areas where you want to add transparency.
If you are only creating this transparency to have white areas in part of the image (such as to have the image fade to white at the outer edges), you may find it easier to add a single layer for this purpose. Start by clicking on the thumbnail for the top-most layer on the Layers panel. You can then, for example, click the “Create Adjustment Layer” button (the half-black/half-white circle icon) at the bottom of the Layers panel and choose “Solid Color” from the popup menu. In the Color Picker dialog that appears, choose white as the color and click OK.
You will now have a white layer that completely covers the image. To hide this white layer from the entire image, click on the thumbnail for the layer mask associated with the Solid Color adjustment layer and then choose Image > Adjustments > Invert from the menu. The layer mask will now be filled with black, blocking the white layer from the entire image.
To paint the white pixels into the image to create the equivalent of transparency for your print, you can now use the Brush tool to paint on the layer mask with white in areas where you want the white pixels created by the Solid Color adjustment layer to be visible.