Blend Modes in Photo Editing

Blend modes unlock a world of creative possibilities, simplifying editing, retouching and restoring photos, and they can save us a whole lot of time! Without them, complex layers could only be merged by working with opacity, whether of an entire layer or by using masks.

Layers - Layers let you place copies of an image, different images, text, masks, graduated fills and adjustments in a sort of stack. Each one separate so what you do to one doesn’t affect the others. Let’s have a simple example:

Open a photo in PSP or a similar editor, go to the Layers Menu and select Duplicate. Now you have 2 copies of the picture and if the Layers Tab is open (View/Tabs/Layers) you will see them on the right hand side as thumbnails. The bottom layer will be labled Background and the one above it Copy of Background. Normally you would rename the copy to something more descriptive.

The Layer blend mode sets the way the pixels in one layer interact with the layer below; how they "blend". A few Blend Modes also interact with the Layer above, too. To get a hold on how Blend Modes work, we are going to alter one of the layer images, then begin playing with its Blend and Transparency.

When you open an image or make a new Layer, the Blend Mode is set to Normal. You will see “Normal” in the Drop Box above the layer thumbnail. Click on the drop box and you will see 20-odd modes listed. The most important for a photographer are probably Multiply, Screen, Overlay, Colour, Hard Light, Soft Light and Luminosity. Understand how and when to use these blend modes and your photo editing becomes a lot easier.

There are 4 factors which decide the what happens when you set a blend mode:

The Base Colours from Image One (usually the lower layer)
Blend Colours from Image Two
The Blend Mode of each layer
The Opacity of each layer

These 4 variables combine to make the colours you'll see in your final Image.

Remember that a Blend Mode specifies how the pixels in one layer interact with the pixels in another. Every Blend Mode makes the Pixels interact differently. Since Normal is the default mode, when it is set and the Opacity is also set to default (100%) all that is visible is the top layer, and it looks...well, ‘normal’.

Try this: Open a new blank image, use your drawing tools and draw a large circle just off centre; fill it with a light blue colour.

Now Make 2 new layers (Raster Layers will work well for this, but any kind will do). Fill each with a white background and on each layer draw a circle. Fill each circle with a different colour. Make sure they are offset a bit, so they all overlap (you may need to reduce the opacity of each layer to 50% to allow the shapes to show through a bit. Set them all back to 100% Opacity when you have finished).

Now for some fun! With all the Layers active you can only see the top one. Mine shows a blue circle on a white field. Click on the Blend Mode drop box and select the first option, which in PSP is Darken - Darken compares the individual pixels in both the base and blend images and uses whichever was darker for the pixel seen in the visible image. Two overlapping circles appear One blue, one green and dark grey where they overlap.

Turn off the top layer (click the eye icon next to the Layer thumbnail) and you will see only a green circle. Now set the Green Layer to Darken, make the top layer visible and all three circles are there with variable greyed-colour overlaps.

Lighten has the opposite effect: it uses the lightest pixels and discards the darker ones. Set the top two layers to Lighten and there isn’t much to see...just a pale pink segment with some non-descript shading; but who says the Blend Mode has to be the same on each Layer? Try some combinations and see what happens.

Let’s set all back to Normal and the top layer to Hue: the background becomes slightly pink and all we see is a red circle (the bottom layer) with a blue segment over it. The Green seems to have gone. The Hue blend mode uses Hues (the colours) of the blend image and combines them with the Saturation (intensity) and Brightness (luminance) from the base image (Green Layer). The result in this case is to only show the part of the blue layer above the Green circle, and make the green circle appear red... that’s right; it isn't the bottom layer you see, but the middle one. Don’t believe me? Turn off the green layer and see what happens; turn it back on and turn off the red. Clever, huh!?

What if you set the middle layer to Hue Mode as well? It’s not what you think...the Green Layer is invisible now, but the Red is visible, still red and overlapped by the blue. Set the Green Layer to Darken, and we get 2 red balls overlapped by the single blue.

Here is a table to get you a bit further into the Layer Blend Game.They apply to PaintShopPro, but other packages are similar enough for this to be helpful:

Normal - pixels on the Blend layer are combined with pixels on the underlying layer, only varying by opacity. (Thus, by moving the opacity slider.)

Darken - pixels in the Blend layer that are darker than underlying layer's pixels will be applied to the image. Lighter pixels will disappear.

Lighten - pixels in the Blend layer that are lighter than underlying layer's pixels will be applied to the image. Darker pixels will disappear.

Hue - applies the hue of the Blend layer to the underlying layers. (there is also a Hue Legacy mode: the current version handles Hue differently than the earlier version; legacy options give the result you expect if you are used to the previous version).

Saturation - applies the saturation of the Blend layer to the underlying layers (also has a legacy option).

Color - applies both the hue and saturation of the Blend layer to the underlying layers, but the luminance is not affected (also has a legacy option).

Luminance - applies the luminance values of the Blend layer to the luminance of the underlying layers, but the colour is not affected (also has a legacy option).

Multiply - combines the colours of the Blend layer with the colours of the underlying layers to produce darker colours Multiplying any colour with black results in black, multiplying with white produces no changes.

Screen - Multiplies the inverse of the Blend layer colours and the underlying layer colours which always results in colours that are the same or lighter than the underlying layer colours.

Dissolve - randomly places some pixels from the Blend layer on the underlying layer, resulting in specks of colour The Opacity slider controls the amount of speckling. You can see a good example in the header of my site at www.davidrichphotography.org where I used it to produce a gold flecking.

Overlay - combines features of the Screen and Multiply modes.It uses the Multiply mode on the shadows; and the Screen mode on the highlights, which lets the base image stand out a lot more than the other two.
For the next two modes, imagine that the Blend Layer has been placed over a light which is then shone o the Base image:

Hard Light - combines features of the Screen and Multiply modes to show highlights and shadows. It works a lot like Soft Light (below), but Hard Light doesn't pay any attention to the highlights or shadows of your base image. What you get is an effect like shining a hard-edged spotlight on the image, but one that uses the blend image for its colours and textures.

Soft Light - combines features of the Dodge and Burn modes so you get soft shadows and highlights. The blend image acts as if it were the light source for the base image. If the blend colour is brighter the base colour gets lightened subtly. If the blend image's colour is darker the base image's colour gets darkened a little.

Difference - subtracts the Blend layer colour from the underlying layer, depending on which is lighter. The result colour has a numerical value which is the difference between the two values. If you know the numerical value of the colours involved, its easy to predict what is going to happen (black=255, white=0).

Dodge - the lightness values of the colours in the Blend layer modify the underlying colours, by making them lighter. The results are a bit like Screen Mode: the result will always be lighter than the base image, except that Dodge draws a lot more on the base image. It lightens the base image, depending on how light the blend image is, but black areas are left untouched.

Burn - the lightness values of the colours in the Blend layer modify the underlying layers, by making them darker. As you’d expect, it is the opposite effect to Dodge Mode. Burn darkens the base image, depending on how dark it is. Where white occurs there is no change.

Exclusion - a watered-down Difference. When pixel values are very different in the two layers, it acts like Difference. But mid-range values stay in the mid range. The effect is like a much softer, lower contrast version of Difference.

Now, what can you do with them? Here are a few ideas:
Tinting and Caste Removal - If you want to tint, or colorize an image easily, create a layer above it and fill the new layer with the colour(s) or gradient etc. you want to tint it with. Then apply the Colour or Hue blending modes. Refine it with the Opacity slider. If you have a colour caste that doesn’t respond to the usual technique using the various colour balance dialogues, try a similar technique.

First, duplicate the layer and name it ‘target’, then choose the fill tool and set the foreground colour to the colour you want to remove or reduce. Open a new Vector Layer above the ‘target’ layer and fill it with the foreground colour. With the Vector Layer selected, invert its colour (Image/Negative Image) and set the Blend Mode to Overlay. Done!

Restore an Old Photo - Multiply blend mode can be used to darken photos that have faded with time without affecting colour in colour images or adding a caste in B&W or sepia photos. It can restore contrast and lost detail to the photograph.

Duplicate the Layer and set the mode to Multiply. You will see that the shadows have darkened and a lot of the contrast and detail have been recovered: If you need to intensify the effect, duplicating the top layer and set the mode to Multiply (again) or to Darken. Use the Opacity slider to fine tune it if the picture is now too dark. Alternatively, you could add a duplicate layer set to Screen Mode, which will not only lighten the overall image, but add some detail to the highlights.

Correcting Exposure - The same technique we used to restore details to the old photo works with overexposed photographs. For underexposed pictures, first increase the contrast by making a duplicate layer and setting it to Soft Light. Screen blend lightens images without affecting the blacks, so once more duplicate the top Layer, and set this new layer to Screen. You can’t rescue every underexposed picture, of course, but most will now have brighter, more contrasty highlights while the shadows will have held their density.

The same process of repeating the duplicate/blend that we used for the overexposed image also works here, and if you wish, you can add a Lighten Mode Layer on top.

Fixing Contrast - This is a primary use for Overlay blending. Dark areas become darker while light areas get lighter and grey tones get cancelled out. It would have been the first suggestion for restoring the old photo (above) except that it often results in a ‘grainy’ appearance. Now if by chance you wanted to add grain to a picture....

Adding Grain - There are many ways to add film-like grain to an image, This is a good one because the grain looks ‘natural’ - i.e. organic, like film. Open a new Raster Layer and fill it with a 50% grey, then set to Overlay. Go to the Adjust Menu and select Add\Remove Noise/Add Noise. In the dialogue box, use the drop-down box to select one of the film grain options, adjust it with the sliders then click OK. The grain is on the grey Layer, and looks all right, but adding a little Gaussian Blur makes it look even more natural.

The Orton Effect - A neat effect that I thought I had lost when I stopped shooting slide film was to take two images of the same scene, one in focus, the other out of focus, and sandwich the two slides together. When it is done with two overexposed slides, it’s called the Orton Effect. Then I discovered Blend Mode Ortons.

In the digital darkroom, open an image and duplicate it. Select the bottom layer and lighten it (Adjust/Brightness and Contrast/ Brightness/Contrast); leave Contrast at 0 and set B rightness at 100. Do the same on the top layer, but set brightness at 50.

Now we have the equivalent of one photo overexposed 1 stop and another 2 stops overexposed.Next we have simulate on “slide being out of focus. Traditionally that would be the slide that is one stop overexposed, but it really doesn’t matter. Go to either Layer and add a small amount of blur. I prefer Average, but many people like to use Gaussian for this. Don’t overdo the blurring: try Adjust/Blur/Average and set a filter aperture of 20.

Now the thing that makes it all work: on the top Layer, set the Blend Mode to Multiple. You should have a soft, Impressionist rendering of the original scene. With the right subject, it almost glows! You may need to reduce the Opacity to really bring the effect out (start at about 75%. For some other nice effects, scroll through the modes on this one: especially check out Luminance, Difference and Exclusion; and then add Burn to the Lower Layer and repeat the exercise.

This Intel is just an introduction to Blend Modes - I hope it tempts you to experiment with them a bit. The outcome is always worthwhile.