Layer Blend Modes

If you have more than one image layer there will be more than one pixel at each position. On the screen of course, you see only one colour for each pixel and this colour depends on how all of the pixels through the layers at that position blend with each other.

If the top layer is set to Blend Mode Normal, then the pixels underneath will have no effect on what you see on the screen (or print out for that matter). On the other hand, Blend Mode Multiply takes the three values (R,G&B) for the pixel in the Blend Layer (top) and similarly for the Base Layer (bottom), performs a calculation on them and produces a Result Colour (screen & print) that is always darker than either of the pixels.

Generally, the easiest way to decide the best blend mode is to cycle through them. You can do this quite quickly as follows:

Click the down arrow on the Blend Mode list
Choose Normal from the top of the list. This will leave the word Normal highlighted in blue – the cycling won’t work unless the highlight is on.
Cycle through with the down-arrow key.
You will notice that Blend Mode Change appears on the History Palette for each change.
Use the up-arrow when you reach the bottom.

A few notes on some of the Blend Modes.

Normal results in the colour of the Blend Layer (top) except where there are transparent or part transparent pixels.
Multiply results in a colour darker than either layer.
Screen results in a colour lighter than either layer.
Overlay tends to increase contrast as lower values are “Multiplied” and higher values are “Screened”
Soft Light and Hard Light have a similar effect to Overlay but are less & more intense respectively.

For Tinting B/W Images with colour, set the Blend Mode of the duplicated (top) layer to Color and paint on the top layer with colours of your choice. But see my notes on Photoshop Hand Colouring for a lot more ideas.

Change the Opacity of the top layer to adjust the degree of the effect.

Neutral Colours

A ‘neutral colour’ doesn’t change when you apply the appropriate Blend Mode. These are the neutral colours for some of them.

Black is the neutral colour for Lighten, Screen, Colour Dodge, Difference & Exclusion.
White is the neutral colour for Darken, Multiply & Colour Burn
50% Gray is the neutral colour for Overlay, Soft Light & Hard Light.

There is no neutral colour for Normal, Dissolve, Hue, Saturation, Color & Luminosity.

If a layer contains White pixels and you set its blend mode to Multiply, then the white pixels become transparent. You can use this technique when you have an image with a completely burned out sky to enable you to reveal a ‘new sky’ layer underneath.