The great thing about digital images is that they are digital, i.e. they exists as a bunch of numbers. These numbers can be subject to mathematical operations. A very important ‘set’ of these operations are called Blend Modes (significantly, in Photoshop 1 they were called Calculations). Blend modes are found all over PS, for example, most Layer Effects feature them and they are available to the brush through the Options Bar. They are also not unique to Photoshop, being found in practically all other digital image applications. Within Photoshop, the most important use of blend modes is in the Layers. These are found in the top of the Layers Pallet.
When painting on a layer set to a blend mode, an artist can darken or lighten a scene with a great degree of control (and also change other values, as the following table describes). A blend mode set to Multiply is a perfect way to add shadows or darkness to a scene and is analogous to the glazing that old master painters used.
The blend mode families
All 23 layer blends are neatly organized into six families. These families are grouped by the similarity of the effect that they have on the image.
Blend mode list
|Dissolve||Affects only the outline of something, making it a bit jagged.||Limited, specialsed use.||*|
|Darken||Darken||A bit like Multiply, but gives a slight polarizing effect||Not as useful as its name implies||*|
|Multiply||Darkens the BG.||The ONLY blend mode for shadow making||****|
|Color Burn||(Applied on a white neutral ONLY) sudden darkening of mid and dark tones||Good for darkening shadows but a bit harsh||**|
|Linear Burn||(Applied on a white neutral ONLY) like a more selective version of Color Burn||Can be used to change color value of a dark area.||*|
|Darken Color||(Applied on a white neutral ONLY) This compares the FG and BG and selects the darkest value||Non wildly useful|
|Lighten||Lighten||A softer version of Screen||Not as useful as its name implies||*|
|Screen||Lightens things||Good for adding soft reflected light, caution: lightens darks as well||**|
|Color Dodge||(Applied on a black neutral ONLY) sudden lightening of mid tones, unlike Screen it will not affect dark values which makes for a more realistic lighting effect||Good for adding highlights or brightening sunsets||***|
|Linear Dodge||(Applied on a black neutral ONLY) like a more selective version of Color Dodge||Good for adding highlights or brightening sunsets||*|
|Lighten Color||(Applied on a black neutral ONLY) This compares the FG and BG and selects the lightest value||Non wildly useful||*|
|Contrast||Overlay||Darkens with the dark FG values, lightens with the light FG values (i.e. adds contrast)||Great for adding texture detail Tip: desaturate to ensure that color values are passed on separately. Also, ensure that the image is generally of a middle value in order to avoid excessively darkening or lightening the FG.||***|
|Soft Light||A softer version of Overlay.||Good for adding a slight color cast to the FG image (e.g. warming or cooling it). Can emulate a photo filter.||**|
|Hard Light||A harder version of Overlay||*|
|Vivid Light||A super hard version of Overlay||*|
|Linear Light||A more even version of Vivid Light||*|
|Hard Mix||A very hard version of Overlay||Similar to the Posterize adjustment, special effect only||*|
|Comparative||Difference||Compares the FG and BG and shows the difference||Great for comparing before and afters, or for aligning two layers||**|
|Exclusion||Inverts for white, no change for black, grey is grey||Looks interesting, go find a use for it, dammed if I can||*|
|Subtract||Similar to Difference||*|
|Divide||Like a white Difference mode||*|
|Value Based||Hue||Passes on the FG hue values onto the BG||Good for changing the hue of objects without affecting other values, only works on BGs with a Hue value||**|
|Saturation||Passes on the FG saturation values onto the BG||Good for saturating / desaturating BGs, the hue of the FG is irrelevant||**|
|Color||Passes on the FG saturation and hue values onto the BG||Good for adding red to cheeks||***|
|Luminosity||Passes on the FG luminosity values onto the BG||Similar to overlay, but has no neutral value. A solid mid grey will eliminate all light and dark tones and leave behind hue values. Obscure.||*|
When painting on blend mode layers, it is frequently required that very low flow rates are required. It is not unusual for a flow rate as low as 1 to be used. Even lower rates can be synthesized by changing the Spacing value of the brush.
Most blend modes have a color that does not 'register'...a color that is invisible to that mode. See for yourself: make a new layer above a photo or image and paint on that layer with white. Then set the blend mode of that layer to Multiply. See the black appear to become transparent.
This behavior is elegant proof of the underlying maths of these modes. All colors are understood as being collections of numbers between 1 (white) and 0 (black). 1 multiplied by any value equals 'no change', hence white has no effect on the background colors when set to multiply.
This knowledge is useful when adjusting Blend Mode layers (usually destructive adjustments are fine with such layers). For example: if you are using a random texture set to Overlay to add interest to an image, then its effect can be lessened by passing a Curve on it and lifting its two ends so that the curve approaches the mid grey horizontal line. Similarly, the effects of a Color blend mode can be lessened by desaturating it with a Hue Saturation.