Blending modes: Tools for post-processing
In previous articles, we've covered setting up and capturing an image - location lighting, studio lighting and rules of composition - both interpreting and breaking them. In this article, we will touch on some tools to help you deal with your images after the capture.
This article takes a look at a couple of the 'blending modes' available in Adobe Photoshop. Blending modes present us with easy-to-use but powerful tools for image manipulation. Best of all, they don't cost anything, beyond the purchase price of the software itself!
Blending modes dictate how the pixels of a given layer are mixed with those of the layers beneath it. Although this article deals with Photoshop specifically, there may be equivalent techniques available in other photo editing software packages.
Throughout this article, we will be discussing images with multiple layers. To keep our terms unambiguous, I will refer to the original layer as the 'base' layer and any layers added to adjust or retouch the image as 'blend' layers.
'Color' Blending Mode
To start our exploration of digital blending modes, I will first present an example based in in analog photography. I was always fond of technical experimentation in the darkroom; this image was made on an enlarger by laying tissue paper over unexposed photographic paper and blotting it with water. The tissue paper diffused the enlarger's image, while the water on the print's surface retarded the action of the developer, creating the light-colored blotches. I then toned the print with a copper / sepia toning agent.
|Early work, an image from my days as an art student. The print has become
discolored from pollutants after being framed with a non-archival mat.
Industrial strength stain remover
Over the years, this print started to become discolored from being in a frame with a non-archival mat. The chemicals in the mat caused portions of the image to turn yellowish. How might we use our digital toolkit to restore the image?
One might attempt to use the healing brush or clone stamp tools to touch up the discolored areas. However, doing this in a way that preserves the texture of the image would be very tedious. Alternately, we could generate one or more complicated hue / saturation adjustment layers to return the colors to their original values. This would require quite a bit of careful tweaking and masking.
Fortunately, there's an easier way. Since the discoloration has not affected the luminance of the image, we can simply use a 'color' blend layer to fix the image. The 'color' blending mode is straightforward - it applies the colors of the blend layer to the pixels in the base layer, but preserves the luminosity and saturation of pixels in the base layer.
|'New layer' dialogue (Ctrl + shift + n / Command + shift + n). Here, we create a new layer and set its blending mode to 'color'.|
The easiest fix would be to use the eyedropper tool to sample a 'good' color and use the brush tool to paint on our 'color' blend layer where the discolored areas are. This produces perfectly acceptable results:
However, the original image does have a range of tones - some of the colors are ochre while others are more greyish-brown. Using a single color to retouch our image removes some of the dimensionality of the original. To address this, we can sample multiple colors and paint semi-overlapping strokes with a large, soft brush set to moderate opacity (for example, 50%).
|This blend layer has a range of colors, sampled from different parts of the source image.||The result is a slightly richer image that is more faithful to the original print.|
The difference between the two treatments is extremely subtle; for some images, the extra work may not be worth the effort.
Pro tip: when using the brush tool, you can sample a color by holding down alt / option and clicking on the desired color. There is no need to switch to the eyedropper tool.
Like digital mittens
Another application of the color blending mode is to adjust skin tone; this is useful in cooler climates such as Seattle, where I live. Models' extremities can often take on a purplish or reddish hue in cold weather.
|Her legs and face look normal, but note the skintone of the model's hands; they have a slightly pink or magenta tone from her sitting on the chilly concrete floor.|
Again, the technique is the same as what we used above - brush (or clone) areas with normal skintone onto the areas of the body whose color has been affected by the cold.
This is a situation where finesse and restraint is required; creating a correction layer by painting with a single color can leave the subject looking very unnatural and clay-like. The blend layer below was created by painting multiple sampled colors with the brush tool.
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