IG Designs says…

When I just started to learn Photoshop my worst nightmare was the Blend (or blending) Modes drop down menu.
All the other tools and options were quite ok but this one. I spent a lot of time trying to get my head
around it and finally I succeeded. Now this beast is serving me well
Now I’ll try to save some time for someone who is going the same way because I’m good!
Here is a description of Blending Modes, groups, options and shortcuts divided in a groups as they
are in Photoshop.

There are 27 of them plus one (I’ll explain that later on). Fortunately Adobe developers grouped them together by similar function.
First of all – you can  navigate through all the Blending Modes by pressing Shift “+” or Shift “-”
Almost every mode has it’s own shortcut, I’ll list them all later on.
And one last thing before we begin – (Alt) for Windows = (Option) for Mac… But you knew that, didn’t you?

When you use blending modes try to think of them in terms of three colours:
1) The base colour – the original colour of the image.
2) The blend (or blending) colour – the one is being blended.
3) The result colour – speaks for itself.

Some of the modes have Neutral colours, the colours that won’t have any effect when they’re blended. If there will be any I’ll specify them for every particular group of modes.

To make some examples I’ll blend together these two images:

So the very first group on the top contains up to four modes:
Normal (Alt+Shift+N) – The default mode. Nothing blends. The most commonly used by the beginners (including myself time ago)

Dissolve (Alt+Shift+I) -  Edits pixels to make them the result colour. The result colour will be a random replacement
of the pixels with the blend colour or the base colour depending on the opacity at every pixel location.
It’s never a combination of both. Lowering the opacity reveals kind of dotted effect. Example below is set to the opacity of 50%. Just to make the effect visible.

When you use the Fill command or the painting tools you’ll get two more modes listed:

Behind (Alt+Shift+Q) – Affects only the transparent areas of the layer. It’s like if you’d be paining on the back of the image. Works only in layers with unlocked transparency – first little icon to the word Lock on the top of the Layers panel.

Clear (Alt+Shift+R) – Same as using the Eraser tool. Makes all affected pixels transparent. Again: transparency must be unlocked.

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The Second group. The darkness prevails!
It have a neutral colour of white.
White simply disappears if it’s blended. The darker blending colour you use the stronger effect you’ll get.
Lowering the Fill on any of the second group modes will give you same effect as lowering the Opacity on the Normal mode.

Darken (Alt+Shift+K) – Selects the darker of the base or blend colours in each channel. Pixels lighter than the blend colour are replaced, the darker ones don’t change.

Multiply (Alt+Shift+M) – Multiplies the base colour by the blend colour. The result is always darker. For instance multiplying any colour with black gives you black.

Color Burn (Alt+Shift+B) – Darkens the base colour to reflect the blend colour by increasing the contrast. The result is always darker and more contrast.

Linear Burn (Alt+Shift+A) – Darkens the base colour to reflect the blend colour by decreasing the brightness and clips values while doing so. Basically it’s a combination of Multiply and Colour Burn modes.

Darker Color (No keyboard shortcut) – Displays the lower value colour of the total channel values for the blend and base colour. It does not produces a third colour, wich can result from the Darken blending, because it chooses the lowest channel value from both already existing colours to create the result colour.

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The Third group. The power of light!
This group have a neutral colour of black.
Black as the blend colour will have no effect. The lighter blending colour you use the stronger effect you’ll get.
And again – using the Fill slider with these modes will give same effect as adjusting the Opacity.
These modes are the inverses of the darkening modes.

Lighten (Alt+Shift+G) – Selects the lighter of the base or blend colours in each channel. Pixels darker than the blend colour are replaced, the lighter ones don’t change.

Screen (Alt+Shift+S) – Multiplies the inverse of the base colour and the blend colour. The result is always lighter. For instance multiplying any colour with white gives you white. Screen mode reduces the contrast.

Color Dodge (Alt+Shift+D) – Lightens the base colour to reflect the blend colour by decreasing the contrast. The result is always lighter. This mode is an exception to the Neutral colour rule. This lightning mode is the only one that preserves black. This mode increases contrast but may clip the brighter areas of the lower colours to white.

Linear Dodge (Alt+Shift+W) -  Lightens the base colour to reflect the blend colour by increasing the brightness and clips values while doing so. Basically it’s a combination of Screen and Colour Dodge.

Lighter Color (No keyboard shortcut) – Displays the higher value colour of the total channel values for the blend and base colour. It does not produces a third colour, wich can result from the Lighten blending, because it chooses the highest channel value from both already existing colours to create the result colour.

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The Fourth group. Mix em all!
This group have a neutral colour of 50% gray.
It means that all of the light modes (except for Overlay) will lighten the image when using colours lighter than 50% gray and darken when using colours darker than 50% gray. As long as it happens on a channel-to-channel basis they can both lighten and darken at the same time. Sounds a bit messy isn’t it?

Overlay (Alt+Shift+O) – Colours lighter than 50% gray are screened, colours darker than 50% gray are multipied. The base colour is mixed with the blend colour to reflect the darkness or lightness of the original colour.

Soft Light (Alt+Shift+F) – If the blend colour is lighter than 50% gray, the image is lightened (same as dodged). If the blend colour is darker than 50% gray, the image is darkened (same as burned). Painting with white or black does not result in pure white or black. It uses gamma ajustments to lighten or darken the image.

Hard Light (Alt+Shift+H) – If the blend colour is lighter than 50% gray, the image is lightened (same as screened). If the blend colour is darker than 50% grey, the image is darkened (same as multiplied). Painting with white or black results in pure white or black. This mode is useful for adding shadows to your image.

Vivid Light (Alt+Shift+V) – If the blend colour is lighter than 50% gray, the image is lightened dy decreasing the contrast. If the blend colour is darker than 50% gray, the image is darkened dy increasing the contrast. Basically, this mode uses color burn to darken and color dodge to lighten.

Linear Light (Alt+Shift+J) – If the blend colour is lighter than 50% gray, the image is lightened dy increasing the brightness. If the blend colour is darker than 50% gray, the image is darkened dy decreasing the brightness. This mode uses linear burn to darken and linear dodge to lighten.

Pin Light (Alt+Shift+Z) – Replaces pixels depending on the blending colour. If the blending colour is darker than 50% gray, pixels lighter than that will be replaced, and pixels darker than that won’t change. If the blending colour is lighter than 50% gray, pixels darker than that will be replaced, and pixels lighter than that won’t change. Pin Light uses darken or lighten modes.

Hard Mix (Alt+Shift+L) – Lighter colours lighten, darker colours darken. To get less threshold/posterization just lower the Fill.

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The Fifth group. Feel the difference.
A neutral colour for the Difference, Exclusion and Substract modes in this group is black. For the Divide mode it’s white.

Difference (Shift+Alt+E) – Evaluates each channel and substracts either the blend colour from the colour base or vice versa, depending on wich colour has the greater brightness value. Blending with white inverts the base colour value.

Exclusion (Shift+Alt+X) – Similar to the Difference mode but lower in contrast. Blending with white inverts the base colour value, blending with black does not give any effect.

Subtract (No keyboard shortcut) – Subtracts the blend from the base. Available only in CS5.

Divide (No keyboard shortcut) – Divides the blend from the base. Available only in CS5.

The last two may be used for different lens corrections (to remove vignetting, lens defects etc.) as well as for HDR toning tricks.

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The Sixth group. The last one.

Hue (Shift+Alt+U) – This mode uses luminance and saturation of the base colour and the hue of the blend colour for the result.

Saturation (Shift+Alt+T) – Uses luminance and hue of the base colour and saturation of the blend colour for the result.

Color (Shift+Alt+C) – Preserves grey levels. Useful for colouring.

Luminosity (Shift+Alt+Y) – Its an inverse of the Color mode.

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So we’re done with Blending Modes… Almost.
There is one more unique blending mode wich is accessible only when a Layer Group is selected.
Do you remember I said 27 plus one in the beginning? Yes, I meant this one.

Pass Through (No keyboard shortcut) – Allows any blend modes, advanced blending options, opacity and fill values that apply to layers within a Group, to affect layers below the Group in the Layers panel. Chaging to Normal mode will restrict that.

That’s it. Now for real
Hope this article will help you to understand those modes a bit better than before.
Have a nice day!