Digital editing expert Hans Weichselbaum brings us the first half of an in-depth look at blending modes
Everybody working in Photoshop will be familiar with layers. After all, they’re one of the many assets of this program, but very few users take advantage of the layer blending modes. In general, there is more than one way to achieve a certain outcome in Photoshop, but quite often a simple change in blending mode, perhaps in combination with a layer mask, can get you there quicker and with less effort.
Here, I run through most of the available blending modes, with a short description of what each does. In a follow-on article next issue I will show you how to make use of blending modes in your day-to-day photography. Editing programs other than Photoshop (Corel PaintShop Pro and Photoshop Elements, for example) also use layers and blending modes.
Perched near the upper-left corner of the Layers panel you will find the pop-up menu for blending modes with a long list of choices.
Open an image, duplicate the layer, and then use the keyboard to cycle through the blending modes: press and hold the shift key then tap the plus key to go forward through the blend menu, and use shift and minus to go the other way.
You’ll find blending modes all over Photoshop, for example in the Layer Style dialogue box, with some of the filters, and in the Fade dialogue box. Some tools also make use of blending modes, including Brush, Paint Bucket, Healing and Cloning Brush, Gradient, and Smudge.
If you are working on a single image, rather than a composite of two or more images, then it’s better if you use an Adjustment layer instead of duplicating the image layer — it won’t double your file size. Simply put an adjustment layer on top of your image — it doesn’t matter which one you choose — and change the blending mode.
Looking at the long list of options, you might notice Photoshop groups them into six clusters. The default setting is Normal, and this behaves as you would expect when you put one image on top of another: the top image simply covers the one underneath, like a sheet of paper. If you change the blending mode to anything other than Normal, Photoshop applies some maths to change the appearance of your image.
I will demonstrate the various blend options with two layers: a blue sphere on top, and two red gradients in the bottom layer.
The first group: Normal and Dissolve
These two modes are at the very top of the list. We just looked at the Normal blending mode, which basically does nothing — there is no interaction between the active layer (the one you have selected) and the one underneath. Of course, you can still reduce the Opacity of the top layer to make it semi-transparent and let the image underneath shine through. Reducing the Opacity is also the way to go if the effect of one of the blending modes is too strong.
The Dissolve blend is quite unique, and there are not many applications for which you will find it useful. Most of the time you won’t see any change in the image at all. That’s because this mode only affects transitions between opaque and partially transparent pixels in the top layer. To make the effect visible I had to reduce the opacity of the top layer (I used 70 per cent). The texture effect is similar to what you often see as a transition effect in slide shows.
Darkening modes
The members of the next section of blending modes all have a darkening effect.
White is the neutral colour for all these blending modes. The effect is that any areas of white in the upper image will disappear, showing the colours of the underlying image.
The first mode of this group is simply called Darken. I didn’t include it with the examples shown, because its effect comes up as very similar to the Multiply blend. The Multiply mode multiplies the pixel values from the two layers, and then divides the product by 255 to normalize the value, getting it back into the allowed range. Think of two slides sandwiched together and projected from one projector. Perhaps that’s a difficult thing to visualize for the new generation of digital photographers, but take my word for it, the result will be a darker image. In practice you can use the Multiply mode to add density to an image that is too bright.
Colour Burn involves some complicated maths. Similar to Multiply, it darkens and increases contrast in the underlying image, then applies the colour from the upper layer to the bottom image, but as a function of how dark that colour is. When you use it on a layer filled with 50-per-cent grey, it intensifies the colours on the layer below. You can use it to fix an ugly sky in a hurry.
Linear Burn is a combination of Multiply and Colour Burn, but it only darkens based on the underlying colour values without having an impact on contrast. It has a tendency to turn dark pixels into solid black.
The Darker Colour mode compares the base and top colours and keeps the darkest pixels. No blending is going on here — the lighter colours just vanish. It is ideal for removing white backgrounds. You can create some cool effects with this mode.
Lighten blending modes
Not surprisingly, all these modes will lighten your image. Black is the neutral colour, and any black pixels in the upper layer will disappear, leaving the underlying pixels unchanged. Anything lighter than black has the potential to lighten the layer below.
Again, I left out the first mode, Lighten, because the effect is very similar to Screen. All the colours are compared, and Photoshop keeps the lightest ones from both layers.
Screen is the inverse of Multiply. It’s like projecting two slides onto the same spot with two projectors. This blending mode comes in handy when you want to extract shadow detail. You can also simulate a multiple-exposure image by blending a number of slightly underexposed images together.
Colour Dodge lightens your image by decreasing its contrast. Light pixels tend to turn into solid white, but it keeps black pixels. Using this blending mode on a layer filled with 50-per-cent grey, you can give dark hair instant highlights.
Linear Dodge lightens your image by increasing its brightness. In general, this isn’t a blending mode you’ll often use, because it tends to turn all light colours into white. More often than not the image will look unnatural.
Lighter Colour not only lightens, but also increases the saturation. It is the opposite to Darker Colour, and you can get some unexpected results. Photoshop compares the base with the top colours and keeps only the lightest pixels. It doesn’t combine any colours.
Contrast modes
This is a group of seven blending modes. The neutral colour here is 50-per-cent grey. Any pixels lighter than middle grey in the top layer will lighten the underlying image, while any darker areas will darken the bottom image. It’s like a combination of Darken and Lighten modes. The result is an increase in contrast.
I use the Overlay blend a lot in combination with the High Pass filter to enhance local contrast, making the image look sharper. If the effect is too strong, you can always reduce the Opacity setting. Seasoned Photoshop jockeys do all their portrait retouching non-destructively with the Dodge and Burn tools in Overlay or Soft Light mode. Soft Light does almost exactly the same as Overlay, but more subtly.
Hard Light is a combination of Multiply and Screen modes. It is the equivalent of shining a harsh light on your image.
In the Vivid Light mode, Photoshop applies Colour Burn to increase the contrast of colours darker than 50-per-cent grey, and Colour Dodge to decrease the contrast of colours lighter than middle grey.
Linear Light is similar to Vivid Light, except that it adjusts the brightness rather than the contrast of the underlying image.
Pin Light is great for producing some special effects in combination with creative filters. It combines the Darken and Lighten blending modes, switching between the two depending on whether the pixels of the upper layer are lighter or darker than middle grey.
With Hard Mix you get a particularly strong result because all the colours are reduced to the six primaries: red, green, blue, cyan, magenta, and yellow (plus black and white).
Comparative blending modes
These should really be called ‘psychedelic’. They can turn your photos into some freaky-looking specimens, which might come in handy for a Halloween card.
The Difference mode compares the pixel values between the two layers. What you see is the difference between the two, but represented as the absolute value (always a positive number). This mode is useful when you want to locate the mid tones of an image. You can also use it to align two layers of the same image (for example, two shots at different exposures).
Exclusion is similar to Difference but with a less dramatic effect. Blending with white inverts the base colour, and blending with black doesn’t do anything.
These are also called the ‘HSL’ modes. They break up the colours in the active layer into three parts: Hue (the basic colour), Saturation (colour intensity), and Luminosity (brightness).
The Hue blending mode applies the hue of the active layer to the underlying image, without changing saturation and brightness. Saturation and Luminosity work similarly, only affecting one parameter. The Luminosity blending mode is particularly useful when working with the Unsharp Mask filter when you don’t want to get any colour artefacts.
The Colour blending mode is a combination of the Hue and Saturation modes. Photoshop keeps the luminance of the underlying layer, and picks up the colour and saturation of the top image. This makes it handy for colourizing greyscale images.
And there is more …
There are other blending modes, for example, the Pass Through mode for layer groups. And the Brush, Pencil, and Shape tools have two additional blending modes, Behind and Clear.
Don’t worry if you haven’t got your head around all the blending modes at this point. The best way of exploring them is to experiment. Start on a single image with an adjustment layer on top. The important points to remember are that Multiply builds up density, Screen makes the image lighter, Overlay increases the contrast, Colour changes the colour balance without affecting luminosity, and Luminosity allows you to sharpen images without the dreaded colour fringes. Don’t forget that you can reduce the strength of the effect by reducing the opacity of the top layer.
Needless to say, the possibilities are only limited by your imagination. In next issue’s article I will show you some practical applications for these techniques in your day-to-day editing work.
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