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RGB image

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Red Channel

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Green channel

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Blue channel

The relationship between highlights and shadows is a critical aspect of any image. Photographers have been trained to become highly sensitized to these relationships. Today, photographers have more control and greater precision than ever before over these key visual elements, using the digital darkroom. In Photoshop, the type of adjustment chosen will provide very specific control. The specificity of an adjustment can be further refined by using a mask. One type of mask yields extreme precision and is derived directly from the light and dark relationships within an image, a luminance or contrast mask.

A contrast mask will allow you to target a specific range of tones without affecting the others; highlights, shadows, and even midtones. In the analog darkroom it’s quite challenging and time consuming to make contrast masks; in the digital darkroom it’s quite easy to quickly make contrast masks. And, you can refine or modify them infinitely and indefinitely.

Here’s how to do it.

Load a channel as a selection and with that selection still active create a layer mask. The quickest way to do this is to go to the Channels palette and while holding the Command key click on a channel – R, G, B or RGB. This will create a selection based on the luminance (light and dark) values of the channel you choose.

With so many choices before you, which channel should you choose? Choose the channel that is light in the areas you want to adjust and dark in the areas you don’t want affected. When in doubt, load the RGB master channel as this will give you a selection based on luminance. If you choose an individual channel (R, G, or B) related hues will become lighter than others and complementary hues darker than others – i.e. in  the red channel reds will be very light while cyans will be very dark.

The active selection outline will appear complex; a dotted line will appear at all 50% gray values, but the whole image will be affected to varying degrees based on the density of the values used to make the selection. As values grow darker the affect reduces; as values grow lighter the affect increases. Remember this mantra, “Black conceals; white reveals.” You can turn a selection into a mask in one of two ways, make an adjustment layer (Layer: New Adjustment Layer)(the selection automatically becomes an adjustment layer mask) or make a layer mask (Layer: Layer Mask: Reveal Selection).

As a mask is comprised of shades of gray its lightness and contrast can be adjusted. Very often, contrast masks can be improved by having their contrast adjusted. Use Curves for the greatest precision in contrast adjustment. Here are a few strategies for doing this. Increase the contrast of a mask and its lightest areas will allow more of an effect to show through while its darkest areas will allow less of an effect to show through. Darken the mask and it will allow less of a correction through. Lighten the mask and it will allow more of an effect through. In special cases, you may want to raise the black point when applying Curves to a mask; this will allow some adjustment to be applied to the deepest values with increasing intensity in the highlights. Conversely, you could lower the white point to reduce the effect in highlights or you could simply reduce the opacity of the adjustment layer.

Would you like to target the shadows instead of the highlights? Invert the mask (Image > Adjustments > Invert or Command I) to reverse the relationship between highlights and shadows; black becomes white and white becomes black.

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Mask inverted

Contrast masks add the ability to target highlights and shadows to any color adjustment tool that does not already provide this function and to all filters.

Question whether you need a contrast mask when making image adjustments with Curves, which provides the ability to target specific ranges of tone without the use of a mask. If the adjustment you want to make to a specific region of tones in an image is extreme and you want to substantially reduce the affect on adjacent tones, then, and only then consider using a contrast mask in combination with Curves. Guard against introducing posterization when doing this.

Classically, photographers use a contrast mask when darkening very bright highlights or lightening very dark shadows. For these types of corrections, where industrial strength methods are required, consider using the blend modes Multiply (for highlights) or Screen (for shadows) in combination with a contrast mask to reduce the affect on the opposite end of the tonal scale and prevent loss of detail.

Today, photographers have additional opportunities to enhance color images using contrast masks. In addition to affecting the lightness (luminosity) of highlights or shadows, you can affect their hue and/or saturation. Compare these three solutions; an image with lightened highlights; an image with warmed highlights; and an image with saturated highlights. All three versions will appear more luminous or filled with light, but the qualities of light in each one will differ. After you’ve tried this, try making opposite moves in the shadows. Once you’ve done these experiments, you’ll start seeing new potential in every color image.

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Highlight lightened

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Highlight warmed

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Highlight saturated

Never have we had so much control over the quality of light within our images. Imagine the possibilities. Better yet, experience them. A world of possibilities for image enhancement will unfold before you.

Read more about masking here.

View more in my DVD Drawing With Light.

Learn more in my digital photography and digital printing workshops.

BeforeAfter

There are many things you can do in Photoshop to make the most of shadow and highlight detail in images, even if you didn’t bracket exposures for HDR.

Curves

Curves, the most precise tool for modifying brightness and contrast, allows you to target and adjust shadows and highlights independently of one another. You can use it to reduce contrast and render more detail in very bright highlights and/or very dark shadows. The Curves interface has a feature (The icon looks like a finger with up and down arrows.) that allows you to click on any area of an image to place a point and adjust those values. If you’re adjusting highlights and shadows, it’s quite likely that you will also have to adjust values in the other end of the tonal scale and possibly midtones to generate the best results. Keep it simple; it’s surprising what you can do with just two or three points. Keep it smooth; avoid posterization by not flattening areas of a curve. The Blend Mode Luminosity can be used to remove any unintended shifts in saturation; more contrasti increases saturation while less contrast decreases saturation.

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Curves can be used to lighten shadows and/or darken highlights

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Before Curves

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After Curves

Shadows/Highlights

The Shadow / Highlight feature in Photoshop (Image > Adjustments > Shadow Highlight) can be very useful for more challenging images. It cannot be applied as an adjustment layer but it can be applied as a smart filter. To preserve future flexibility, apply Shadows / Highlights applied to the Background Layer converted to a smart object or to a duplicate Background layer if you plan to use Blend If sliders.

At first glance, Shadows/Highlights appears to offer two simple Amount sliders. Check Show More Options and you’ll find more sliders. The Tonal Width slider specifies which values are and are not affected, similar to a luminance mask. The Radius slider applies a sharpening affect, similar to High Pass filtration, to the affected areas only; this is the slider that does what no other tool does. Additionally, you can apply Color and Midtone adjustments – but there are other better ways to do this.

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The Radius slider in Photoshop’s Shadows/Highlights provides affects not found in other tools

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Before Shadows/Highlights

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After Shadows/Highlights

Screen / Multiply

You can make industrial strength adjustments to an image using the Blend Modes Multiply and Screen found in the Layers palette. (Use the pull down menu that defaults to Normal.) Multiply dramatically darkens an image; it’s like registering two transparencies on a light table. Screen dramatically lightens an image; it’s like registering two projected images on a wall. These effects can be very helpful in making very bright highlight and very dark shadow detail more visible. Blend modes can be applied with any layer. They can be combined with Curves adjustments for even stronger effects. Because their effects are so strong you’ll want to modify their intensity using the Opacity slider or restrict their effects using Blend If sliders or a contrast mask.

Read more about Photoshop Blend Modes here.

Blend If Sliders

To restrict an adjustment to either the shadows, midtones, or highlights, you can use the Blend If sliders found in the Layer Style menu. Double click on the layer (Not the icon or the name, but the area to the right of them.) to activate the Layer Style menu. Then use the sliders in This Layer to remove the effect on the background layer. For smoother transitions, feather the effect by holding the Option/Alt key and splitting the sliders apart.


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T Layer Style dialog with Blend If sliders set to target shadows

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The Layer Style dialog with Blend If sliders set to target highlights

Luminance Masks

To more precisely target a specific range of the tonal scale, you can quickly make precise luminance masks in Photoshop. Simply go to the Channels palette and Command/Control click on the RGB channel. This will load a selection of the highlights. If you want to create a selection of the shadows go to the Select menu and choose Inverse. Then simply make an adjustment layer and the selection will automatically become a mask or target a layer and click the mask icon at the bottom of the Layer palette. You can further modify the brightness and contrast of the mask by applying Curves to it (Image > Adjust > Curves).

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Highlight mask shadowmask

Shadow mask

Read more about luminance masks here.

Blending Channels

Do you still want more? If dynamic range issues persist in one channel (or even two), you can use the information in the other channel(s) to improve it. Use Photoshop’s Channel Mixer or use a duplicate layer’s Layer Styles. It’s a complex technique, but it’s there when you really need it.

Read more about blending channels here.

For even more dramatic effects these methods can be used in combination with one another.

To Merge Or Not To Merge

All of this might make you wonder why you’d ever need to bracket exposures for HDR merges. Actually, there are plenty of times – when the dynamic range of a scene far exceeds the dynamic range of a camera’s sensor. You can use all of these techniques in combination with HDR merges to get optimum results. Knowing why and why not to use HDR merges, when and when not to use them, and how far to go or not go with them will help you master them.

Read more on HDR techniques here.

Learn more in my digital printing and digital photography workshops.


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