Today’s Question: As something of a follow-up to your answer about Flow versus Opacity for the Brush tool in Photoshop, can you help me understand the difference between Opacity and Fill on the Layers panel? I believe you’ve addressed this in the past, but I can’t figure out the difference.
Tim’s Quick Answer: Both the Opacity and Fill controls on the Layers panel in Photoshop enable you to reduce the opacity of the current layer. When you reduce the value for Fill, however, the opacity of layer effects is not reduced.
More Detail: If you perform a simple test of the Opacity and Fill controls found on the Layers panel in Photoshop, you might reasonably conclude that they both do the exact same thing. With a simple image layer, for example, both of these controls would reduce the opacity of the layer in the exact same way. That’s because both Opacity and Fill will reduce the opacity of pixel layers with the same effect.
However, as noted above, the Fill control will not reduce the opacity of layer effects, such as a drop shadow or border stroke applied to an image layer. So, for example, you could reduce the opacity of the image using the Fill slider and the border effect created with the Stroke layer style would remain at full opacity.
This flexibility can be helpful in creating some interesting effects. With a composite image you can reduce the opacity of one or more image layers using the Fill control so the layer effects you’ve applied at full strength. And of course if you want to reduce the opacity of the layer effects in addition to the pixels, you can use the Opacity control rather than Fill.
One creative way that I sometimes take advantage of the behavior of the Fill control is to apply layer effects to a text layer and then reduce the opacity of the text with the Fill control. This will reduce the opacity of the text, while leaving the layer effects at full strength. Sometimes I’ll even set the Fill setting to 0% so the text completely disappears, but with the layer effects such as drop shadow at full strength. This creates an interesting result where you can only read the text because of the effects that surrounded the text, since the text itself isn’t visible at that point.
