Tonal contrast is the difference between dark and light

Tonal contrast
Tonal contrast is the difference between dark and light areas of an image. Adjustments in this area can give an image added overall ‘punch’ and add interest to areas of the image to assist compositional elements achieve a flow. I find it’s rare for one global contrast adjustment to benefit all parts of the image to the same degree. Therefore the key to all contrast adjustments, especially tonal contrast, is to apply it selectively to areas of the image and to selective tones. This, in effect, is providing `local contrast’. One quick way to control local contrast is to use the clarity slider in Lightroom or Adobe Camera Raw. This effectively increases the contrast within ‘mid-tones’ and applies the effect to the whole image. If you wish, you might introduce local contrast selectively in Lightroom using the various filters or the adjustment brush. Your selections however, are limited to the fineness of the brush in Lightroom, and its automatic selection of mid-tones using the ‘clarity’ function. Use the following steps as one method to gain finer control of tonal contrast in Photoshop.

Step 1: In Photoshop, using the curves adjustment layer allows you to select the contrast adjustments at any part of the tone curve via the top left icon on the curves palette. Click on that icon then move the cursor over a bright part of the image and left click to insert a point on the tone curve. Move the icon to a dark part of the image and left click again and another point is inserted on the tone curve. You now have two basic points from which you can adjust the curve rather than guessing where to begin your adjustments. In the curves adjustment layer the steeper the curve at any particular point, the higher the contrast, the flatter the curve, the lower the contrast.

Sample 1:
Port Campbell National Park, Victoria. Generally a mix of warm bright tones and cool dark tones makes for a more effective image, so we work in post-production to maximise that effect.

Sample 2: Hopetoun Falls, Great Otway NP, Victoria. These falls can be viewed from a platform only a short walk from the carpark, or descend about 200 steps to really get up close. Nestled amongst lush tree ferns, Hopetoun Falls is reflected here in the stream leading from the waterfall.
Canon EOS 5DIII, Canon 16-35mm f/2.8L II lens, 1.6s @ f/16, IS0100, tripod, polariser. Two-exposure blend for reflection. Contrast, blur and sharpening done in Adobe Photoshop CC. Image by David Lee.

Sample 3: Adding textural contrast: Gaussian Blur. After duplicating the background layer twice, select the middle layer and use the Gaussian Blur filter (1). This can be found under Filter > Blur > Gaussian Blur. Adjust the slider (2) until the blur is enough to make this layer devoid of detail. Adjust the opacity of the layer (3) until it is at the degree of ‘softness’ you wish and use a layer mask to paint out with a black brush.

Sample 4: Adding textural contrast: High Pass Filter. Select high pass filter by going to Filter > Other > High Pass (1). Adjust slider until detail and texture of the scene is visible (2). Change the blend mode of this layer to overlay in the Layers tab (3).

Step 2: At this stage any adjustment you’ve made is still occurring over the entire image. Our approach is to create a layer mask and fill the mask with black so that all of the effect is `masked out’. We then use a white brush at low opacity to paint in the effect where desired. The advantage of using Photoshop In the curves palette. Click on that over a bright part of the image and a the tone curve. Move the icon to d left click again and another point ft Yon now have two basic points the curve rather than guessing where in the curves adjustment layer the rtiniar point, the higher the contrast, wer the contrast. Idlustment you’ve made is still nip. Our approach is to create a It with black so that all of the effect is I white brush at low opacity to paint The advantage of using Photoshop for the masking process is that complex masks such as luminosity masks can also be used to restrict the effect to varying degrees of lights, darks and mid-tones.

Step 3: One potential pitfall of tonal contrast adjustment is that blacks can be made too black and highlights can become `blown’. Luminosity masks are particularly useful if you want to ensure that the darks or blacks are not obliterated by the contrast adjustment. In order to do this, select a dark luminosity mask using Ctrl left click on the appropriate mask, then ‘fill’ the layer mask with black (Shift F5). You should now have an image with contrast affecting all areas except those dark tones you selected from the luminosity mask.

Step 4: It’s also important to note that at this stage the contrast adjustments you’ve performed have not only affected brightness values, but colour values as well. Severe adjustments of contrast can lead to significant colour degradation to the point of introducing artefacts. To avoid any colour shifts, I’d recommend working initially in luminosity blend mode which only affects brightness values. Once the mask work has been done on this layer, you can independently bring back some colour contrast by duplicating this layer (Ctrl or Command J) and changing the blend mode to ‘colour’. The opacity of the `colour’ blend mode layer can then be adjusted to the level you find most
appropriate for the image.

“Luminosity masks are particularly useful if you want to ensure that the darks or blacks are not obliterated by the contrast adjustment.”