Sunset, Victoria coastline, March 2004 (final version).

This text describes a few variation of controlling contrast using LightZone.

By contrast control I refer to the process of balancing the relative brightness of highlight and shadow areas in a photograph. Traditionally (in a wet darkroom) this process is called masking, or dodging and burning. Masking is performed simply by blocking the light from the enlarger from reaching parts of the photographic paper. In a digital darkroom the process is actually not that different, which we will see below.

For demonstration I am using this photograph:

Sunset, Victoria coastline, March 2004 (orginal photo).

Shooting straight into the sunset, I set up my Ebony SW23 on a beach in southeastern Australia, with a Schneider Digitar 5.6/120 lens and a 3-stop ND graduated filter, then waited for the sun to emerge below the afternoon clouds. Still, the beach is a bit dark compared to the sunset - unadjusted contrast range of the scene probably was in the range of 12-16 stops, even ignoring the sun itself. The exposure was made on Velvia 50. The developed transparency is extremely sharp with a remarkable tonal range, with detail very deep into the shadows in the lower right corner. The scan was made on a Nikon LS-8000 scanner at 4000 ppi, using ICE3, GEM, and 16x multisampling.

Evaluating results of digital image processing

One challenge in a digital darkroom process is to do what comes naturally in the real world - less light means adjusting luminosity only, without any effect on color hue or saturation. Today's most current techniques based on Photoshop fail in this respect - using Overlay blend mode causes color shifts, as does Adobe's Shadows/Highlights filter. If you want to experiment, try this color ramp:

Continuous-hue ramp.

This image contains continuous ramps where hue and saturation is constant, only luminosity changes from left to right. Try to use contrast masking to brighten the left side without brightening the right side, while keeping hue and saturation constant. If you have an editor that can display HSL values, such as Photoshop, then you can measure that values in the ramp before and after adjustments. This is how we test masking algorithms at LightCrafts. This file is in ProPhotoRGB color space, so depending on you web browser it might look flat or saturated. To give it a try, save it and open in your photo editor.

Using LightZone

In LightZone there are two major methods for masked contrast control:

• Contrast Mask, and
• Masked dodging and burning

The text below shows both approaches.

Using Contrast Masking

Lightzone has a pre-built tool for contrast masking - which I am proud to say is of my design, together with Fabio Riccardi. The Contrast Mask tool in LightZone works very similarly to a contrast mask in the wet darkroom - you can set blur radius from sharp to very blurred, and you can set the density of the mask.

First I add a contrast mask tool using its standard preset values:

Contrast Mask tool added, with default settings.

This makes some adjustments, but I do want a stronger effect. I also want to make sure that the radius and density is properly set for this image. So let's take a look at the mask itself. I do this by changing blend mode to Normal and Opacity to 100%.

The actual mask, still default settings.

I find it useful to look at the mask to decide on blur radius. As you can see from the histogram, the mask is not very dense. Increase density, lower radius to get the right density in the highlights. Obviously - from looking at the mask as well as the original image - what needs to be masked is the sun, the reflection in the water and an area around those spots. This is my mask after corrections:

Mask after adjustments to radius and density.

Let's look at the results - I do this by changing the blend mode back to the standard Soft Light blend mode.

Result after changing mask radius and density.

The effect could be perhaps be stronger for this image. Alternatives:

• Add one more CM tool
• Use a different blend mode (Overlay, Multiply, Color Dodge, Soft Dodge)

For this photograph, the Overlay blend mode yields very similar results. Like Soft Light, Overlay gives slight shifts in hue and saturation in the highlights.

The Multiply blend mode: is the most correct blend mode to use, in terms of that it properly models what happens when you in mask light - it only affects luminance while keeping hue and saturation fixed. However, Multiply is a darkening blend mode so an exposure compensation is necessary (can be done using ZoneMapper or Hue/Saturation tool).

Using Multiply blend mode. A ZoneMapper had to be added to compensate for loss of exposure. Notice the clean, unsaturated highlights around the sun, compared to the Soft Light blend mode above.

Contrast Mask with Soft Dodge blend mode lifts up deep shadow detail, it is often most useful on mainly dark photos like this one. The effect is generally too strong, so it has to be faded by reducing the opacity of the Contrast Mask tool - sometimes down to 10%. In some cases Color dodge can be used, although Color Dodge will increase saturation in parts of the tonal range.

Blend mode changed to Soft Dodge. Notice how this blend mode, while still only affecting luminosity, really brings out detail in deep shadows.

To look out for saturation clipping, watch the histogram as you move the opacity slider slowly from the left to the right. Any spikes that appear are signs of saturation clipping. If you see a spike then the effect might be too strong and you have to back off by lowering opacity.

Using ZoneMapper and masking

In this example I create a mask much like an ND graduated filter, to bring up the shadow detail without affecting highlights. In this example I add a ZoneMapper tool, then mask it with a polygon region with wide feathering, then change the ZoneMapper to brighten the shadow areas:

Creating an ND grad filter using a ZoneMapper tool and a mask.

Edits applied, mask still visible.

ZoneMapper in Luminosity mode works extremely well here, you just slap it on, make your adjustment, adjust the position and feathering of the mask and you're done.

Here is the final image, again:

Sunset, Victoria coastline, March 2004.