A Not Actually Very Quick Guide to Blending Modes

So when I first started using Photoshop, I had no idea what all the blending options for layers were. I only used Soft Light for changing colours and Hard Light for sharpening layers.

For a real in depth detailing of blending modes and layers, visit these Adobe's website or Photoblogstop.

 So I'm using this photo of Katie and Shaydeena just as a demonstration. I used an adjustment layer to lower the saturation to -70. This will be the base colour.

 I then went to Layer > New Layer > Gradient... and chose a gradient to be my demonstration layer and the result was as below and this will be referred to as the blend colour.

 Normal  - The default mode. The Blend colour doesn't change and the base colour isn't visible.

Dissolve - Dissolve replaces several pixels of the blend colour using other pixels at random.

 Darken - Darken makes pixels from the base colour darker than the blend colour darker but leaves the pixels that are already darker than the blend colour as they are

 Multiply - Multiply multiplies the base colour by the blend colour. It's good for darkening pictures as long as you are not using black as it doesn't affect black.

 Colour Burn - Colour Burn increases the contrast between the base colour and the blend colour. It doesn't work with white pixels.

 Linear Burn - Linear Burn decreases the colour within the base colour. And as you can see from the pictures above it does not allow as much saturation as Colour Burn and is darker than Multiply. It doesn't work with white either.

 Darker Colour - Darker Colour uses works the same as Darken however it uses different colour channels. (Both sites I've used for reference don't explain why it's solid in my image, but I assume it's because the base colour was very white)

 Lighten - Lighten is the opposite of Darken, it lightens the pixels on the base colour that are lighter than the blend colour and leaves the pixels that aren't lighter.

 Screen - Screen creates an effect that is similar to layering film slides on top of each other. It creates a lighter layer however it has no effect on black or white.

 Colour Dodge - Colour Dodge decreases the contrast between the base colour and the blend colour to brighten the base colour.

 Linear Dodge (Add) - Linear Dodge (Add) increases the brightness within the base colour so it matches the brightness of the blend colour

 Lighter Colour - similar to Lighten and the opposite of Darker Colour. It uses a different channel from Lighten so it doesn't produce a third colour like Lighten does.

 Overlay - Overlay multiplies or screens the blend colour over the base colour whilst preserving the shadows and highlights of the base colour

 Soft Light - Soft Light either lightens or darkens the base colour depending on the blend colour. It does affect white and black on the blend colour as it causes it to either lighten or darken the base colour.

 Hard Light - Hard Light multiplies or screens the base colour depending on the blend colour and it causes a white or black blend colour to create a pure white or pure black.

 Vivid Light - Vivid Light either increases or decreases the contrast of the base colour depending on the blend colour

 Linear Light - Linear light either increases or decreases the brightness of the base colour depending on the blend colour

Pin Light - Pin Light replaces the colour of the pixels within the blend colour depending on how light or dark they are. If the blend colour is more than 50% grey it will replace the light colours whereas if it is less than 50%, it will replace the dark colours.

Hard Mix - Hard Mix is pretty technical and it multiplies the RGB channel values of both colours and manages to convert all pixels to the three primary colours, white and black. 

 Difference - Difference uses the RGB channels as well, however it takes the vale of the least brightest colour away from the brightest colour. However with white it inverts the base colour's value and it doesn't do anything to black.

  Exclusion - Exclusion is almost the same as Difference except it has a lower contrast

 Subtract - Subtract takes away the colour value from the RGB channels within the blend colour away from the base colour

 Divide - Divide is the same as Subtract except it divides the values instead of subtracts

 Hue - Hue uses the luminance and saturation of the base colour and the hue of the blend colour (which explains why my image is really desaturated since the base colour had been almost completely desaturated) 

 Saturation - Saturation is similar to Hue, but it uses the hue and luminance of the base and the saturation of the blend colour.

 Colour - Colour uses the luminance of the base and the hue and saturation of the blend colour

 Luminance - Luminance uses the luminance of the blend colour and the hue and saturation of the base colour (yeah it didn't work out for me)