layer blends

American Patriot - Duncan P Walker www.iStockphoto.com

essential skills

~   Learn the practical applications of layer blend modes for image retouching and creative montage work.

~   Develop skills using the the following techniques:

–   blend modes

–   layers and channels

–   layer masks.

Introduction

When an image, or part of an image, is placed on a separate layer above the background, creative decisions can be made as to how these layers interact with each other. Reducing the opacity of the top layer allows the underlying information to show through, but Photoshop has many other ways of mixing, combining or ‘blending’ the pixel values on different layers to achieve different visual outcomes. The different methods used by Photoshop to compare and adjust the hue, saturation and brightness of the pixels on the different layers are called ‘blend modes’. Blend modes can be assigned to the painting tools from the Options bar but they are more commonly assigned to an entire layer when editing a multi-layered document. The layer blend modes are accessed from the ‘blending mode’ pull-down menu in the top left-hand corner of the Layers palette.

Serena Galante

The major groupings

The blend modes are arranged in family groups of related effects or variations on a theme. Many users simply sample all the different blend modes until they achieve the effect they are looking for. This, however, can be a time-consuming operation and a little more understanding of what is actually happening can ease the task of choosing an appropriate blend mode for the job in hand. A few of the blend modes are commonly used in the routine compositing tasks, whilst others have very limited or specialized uses only. The five main groups of blend modes after Normal and Dissolve that are more commonly used for image-editing and montage work are:

•  Darken

•  Lighten

•  Overlay

•  Difference

•  Hue.

Opacity and Dissolve

At 100% opacity the pixels on the top layer obscure the pixels underneath. As the opacity is reduced the pixels underneath become visible. The Dissolve blend mode only becomes apparent when the opacity of the layer is reduced. Random pixels are made transparent on the layer rather than reducing the transparency of all the pixels. The effect is very different to the reduced opacity of the ‘Normal’ blend mode and has commercial applications as a transition for fading one image into another, but the effect has very limited commercial applications for compositing and photomontage of stills image work.

Image 02 Opacity. The groups of blend modes are listed using the name of the dominant effect. A step wedge is then used to demonstrate ‘Normal’ at 100% and 50% opacity and the ‘Dissolve’ blend mode with the layer set to 50% opacity

The ‘Opacity’ control for each layer, although not strictly considered as a blend mode, is an important element of any composite work. Some of the blend modes are quite pronounced or ‘aggressive’ in their resulting effect if applied at 100% opacity and could be overlooked if the user does not experiment with the combined effects of opacity and blend mode together.

The ‘Darken’ group

It’s not too hard to figure out what this group of blend modes have in common. Although Darken leads the grouping, Multiply is perhaps the most used blend mode in the group.

Image 03_Darken. The Darken mode can replace existing highlights while ignoring darker tones

Darken

The ‘Darken’ blend mode chooses pixels from either the blend layer or underlying layers to display at 100% opacity depending on their brightness value. Any underlying tone that is darker than the blend color remains unaffected by the blend mode, and any color that is lighter than the blend color is replaced rather than multiplied with the blend color. This blend mode is usually restricted to pasting a carefully chosen tone into the highlights of an image.

Multiply is a useful blend mode when overall darkening is required

Multiply

The ‘Multiply’ blend mode belongs to the ‘Darken’ family grouping. The brightness values of the pixels on the blend layer and underlying layer are multiplied to create darker tones. Only values that are multiplied with white (level 255) stay the same.

Image 04 Multiply. The Multiply blend mode is used to darken the top half of the image

Image 05 Multiply. The Multiply blend mode is used to apply a dark edge to the image

Image 06 Multiply. The Multiply blend mode is used to darken the sky in this landscape image

Image 07 Multiply. The Multiply blend mode is the secret to success when masking hair that was first captured against a white background. The new background layer and layer mask is positioned above the portrait and the layer is then set to the multiply mode. Note the difference before and after the blend mode has been applied (see Montage projects > Hair Extraction)

Image courtesy of Shari Gleeson

Image 08 Burn. color Burn

Color Burn and Linear Burn

The image is darkened to reflect the blend color. Color Burn increases the underlying contrast to do this whilst Linear Burn decreases the underlying brightness. This is a difficult blend mode to find a use for at 100% opacity. Saturation can become excessive and overall brightness, now heavily influenced by the underlying color, can ‘fill in’ (become black).

The ‘Lighten’ group

Everything that was mentioned with the Darken group is now reversed for this group of blend modes. The ‘Screen’ blend mode is often considered the favorite of this group amongst photographers.

Image 09 Lighten. Two exposures are combined to balance the bright ambient light and the comparatively dim interior lighting of a building. A second image is captured at night and placed on a layer above the daylight exposure. The layer is then set to the Lighten blend mode – original images by John Hay

Lighten

The ‘Lighten’ blend mode chooses pixels from either the blend layer or underlying layers to display at 100% opacity depending on their brightness value. Any underlying tone that is lighter than the blend color remains unaffected by the blend mode, and any color that is darker than the blend color is replaced rather than multiplied with the blend color. This blend mode is particularly useful for introducing highlights into the underexposed areas of an image. This technique can also be useful for replacing dark colored dust and scratches from light areas of continuous tone.

Image 10 Screen. Screen is useful when overall lightening is required

Screen

The ‘Screen’ blend mode belongs to the ‘Lighten’ family grouping. The ‘inverse’ brightness values of the pixels on the blend layer and underlying layers are multiplied to create lighter tones (a brightness value of 80% is multiplied as if it was a value of 20%). Only values that are screened with black (level 0) stay the same.

Image11. Screen. A background layer is duplicated and a Screen blend mode is applied to lighten all levels

Image 12 Screen. The Screen mode can be used to apply a white border around an image

Blond Goddess -Katja Govorushchenko (www.iStockphoto.com)

Image 13 Screen. The Screen blend mode is useful when masking hair that was first captured against a black background (see Montage > Hair Extraction for more information about this technique)

Girl by Shelly Perry (www.iStockphoto.com)

Image 14 Screen. The Screen blend mode is particularly useful for quickly dropping in elements that were photographed against black background such as smoke, bubbles, splashing or spurting water and fireworks. For transparent elements the lighting is usually positioned to one side or behind the subject matter to create the best effect

Image 15 Dodge. Color Dodge

Color Dodge and Linear Dodge

The image is lightened to reflect the blend color. Color Dodge decreases the underlying contrast to do this while Linear Dodge increases the underlying brightness. This again is a difficult blend mode to find a use for at 100% opacity. Saturation can become excessive and overall brightness, heavily influenced by the underlying color, can blow out (become white).

The ‘Overlay’ group

This is perhaps the most useful group of blend modes for photomontage work.

Image 16 Overlay. Applying the blend mode ‘Overlay’ to a texture or pattern layer will create an image where the form appears to be modelling the texture. Both the highlights and shadows of the underlying form are respected

Image 17 Overlay. The ‘Overlay’ blend mode is useful for overlaying textures over 3D form

Overlay

The Overlay blend mode uses a combination of the Multiply and Screen blend modes while preserving the highlight and shadow tones of the underlying image. The Overlay mode multiplies or screens the colors, depending on whether the base color is darker or lighter than a midtone. The effect is extremely useful when overlaying a texture or color over a form modelled by light and shade. Excessive increases in saturation may become evident when overlaying white and black. The ‘Soft’ and ‘Hard Light’ blend modes produce variations on this overlay theme.

Image 18 Overlay. A 50% Gray layer set to Overlay or Soft Light mode can be used to dodge and burn the underlying image

Note > A layer filled with 50% Gray is invisible in Overlay and Soft Light mode and, as a result, is commonly used as a ‘non-destructive’ dodging and burning layer.

Soft and Hard Light – variations on a theme

The Soft and Hard Light blend modes are variations on the ‘Overlay’ theme. Photoshop describes the difference in terms of lighting (diffused or harsh spotlight). If the Overlay blend mode is causing highlights or shadows to become overly bright or dark or the increase in saturation is excessive then the Soft Light blend mode will often resolve the problem. The Hard Light, on the other hand, increases the contrast – but care must be taken when choosing this option as blending dark or light tones can tip the underlying tones to black (level 0) or white (255).

Image 19 Hard Mix

Hard Mix

The Hard Mix blend mode was new to Photoshop CS. It has a threshold effect when blending desaturated tones into a desaturated layer and a color posterization effect when blending saturated or desaturated tones with a color layer.

Blend modes for tinting and toning

The Hue and Color blend modes are predominantly used for toning or tinting images whilst the Saturation blend mode offers more limited applications. Photo filters were also introduced with Photoshop CS that create similar effects to the Color and Hue blend modes.

Hue

The ‘Hue’ blend mode modifies the image by using the hue value of the blend layer and the saturation value of the underlying layer. As a result the blend layer is invisible if you apply this blend mode to a fully desaturated image. Opacity levels of the blend layer can be explored to achieve the desired outcome.

Color

The ‘Color’ blend mode is useful for toning desaturated or tinting colored images. The brightness value of the base color is blended with the hue and saturation of the blend color.

Image 20 Hue-Color. Hue and Color blend modes

Image 21 Color

Note > Color fills can be used to tint or tone images by setting them to Hue or Color mode. Photoshop’s Photo Filter layers (introduced with CS) perform a similar task but without the need to set the layer to the Hue or Color mode.

Saturation

The brightness or ‘luminance’ of the underlying pixels is retained but the saturation level is replaced with that of the blend layer’s saturation level.

Note > This blend mode has limited uses for traditional toning effects but can be used to locally desaturate colored images. To work with this blend mode try creating a new empty layer. Then either fill a selection with any desaturated tone or paint with black or white at a reduced opacity to gradually remove the color from the underlying image.

Image 22 Saturation. The Saturation blend mode

Image 23 Saturation. A Saturation layer is used to desaturate the underlying image

Luminosity

The ‘Luminosity’ blend mode creates the same result as the ‘Color’ mode if the layers are reversed, i.e. the color layer is underneath. The luminosity values within an RGB image have a number of very useful applications. The luminosity values can be extracted from an RGB image (from the Channels palette) and saved as an alpha channel, used as a layer mask or pasted as an independent layer above the background layer.

Image 24 Luminosity

Creating a luminance channel

1.  In the Channels palette Command/Ctrl-click the master RGB channel to select the luminance values.

2.  Click on the ‘Save selection as channel’ icon to create an alpha channel.

3.  Choose ‘Invert’ (Image > Adjustments > Invert).

A Curves adjustment layer can be switched to Luminosity mode to eliminate shifts in saturation when contrast is increased. The example above illustrates what happens when contrast is increased using a Curves layer in Luminance and Normal blend modes. Open up the file and try it!

Difference and Exclusion

The Difference blend mode subtracts either the underlying color from the blend color or vice versa depending on which has the highest brightness value. This blend mode used to be useful for registering layers with the same content but this has now largely been replaced with the new Auto-Align layers command in CS3 for layers that are not Smart Objects. The Exclusion blend mode works in the same way except where the blend color is white. In this instance the underlying color is inverted.

Image 25 Difference. The Difference mode is used to align two layers

Image 26 Difference. Original image (Harmony) by Nicholas Monu (www.iStockphoto.com)

The Difference mode can also be used to create a ‘solarized’ or ‘sabattier’ effect. Duplicate the layer and go to Image > Adjustments > Invert. Apply the Difference blend mode to the background copy layer. Desaturate the image to create the more traditional look (made famous by the surrealist photographer ‘Man Ray’).

Creating a simple blend

Blending two images in the computer is similar to creating a double exposure in a film camera or sandwiching negatives in the darkroom. Photoshop allows a greater degree of control over the final outcome. This is achieved by controlling the specific blend mode, position and opacity of each layer. The use of ‘layer masks’ can shield any area of the image that needs to be protected from the blend mode. The blending technique enables the texture or pattern from one image to be applied to another image. The texture blended takes on the shadows and highlights of the underlying form but does not wrap itself around the contours or shape of the three-dimensional form unless further steps are taken to displace the pixels. This can be achieved using the Displacement filter (Filter > Distort > Displace) or the Liquify filter.

Image 27 Overlay

Akane Utsunomiya

Chris Neylon