This Master Printing Class is about managing photos with low contrast. It’s an important topic because creating the right amount of contrast is an image is always a key task. The two factors to consider are contrast and perceived detail smoothness.
Why do I mention contrast and detail together? Have a look at Figures 1 and 2. Some will say that Figure 1 has less detail than Figure 2. Actually, they have the same level of detail (Figure 2 is just a lower-contrast version of the first image), but in Figure 1 less detail is perceived by a human observer. This example should demonstrate that more contrast translates into more visible detail.
So why not crank the contrast up as much as possible? First, the maximum contrast that can be created is defined by the output medium. For photo- graphic prints, this can range from 1:50 (matte papers) to 1:250 (some glossy papers). The second and even more important limit is the loss in smoothness that occurs if the contrast gets too harsh. A high-contrast image of fog is a contradiction. If the maximum contrast range is limited by the output medium, then the shadows, midtones, and high- lights actually compete for their parts of the contrast range.
Very often the most important part in terms of contrast is the midtones. They define what you see as content in the image. The highlights and the shadows don’t carry the main detail content and have to be controlled in a way that gives the photo a fine finish. Highlights without any detail will print as plain paper-white and are often very distracting. Watch out that your highlights are smooth, with natural fine detail, but not muddy (quite a challenge here). On the other hand, the shadows should not be blocked, translating into pure areas of black ink on the paper.
Let’s now have a look at the different aspects of controlling an image’s contrast.
The classic Photoshop Levels and Curves tools control the global tonality/contrast. If these tools change the brightness of a pixel, they change all the pixels with the same values everywhere in the image, independently of whether the pixel is in a bright or a dark area of the image. I will explain shortly why that matters. I won’t discuss global contrast much further here, but it is still essential to tune the global contrast as part of your editing process.
To better understand local contrast, let’s examine how the human eye perceives a scene very differently from a camera sensor. The circles in all the rows in Figure 3 have exactly the same brightness. But to human observers, the spots look brighter against dark backgrounds, and darker against bright backgrounds. That’s because the human brain evaluates the contrast between areas of a scene or image relative to their surrounding areas. This is what local contrast is all about: creating an improved relative contrast in the shadows and also the highlights. As I mentioned, tools like Photoshop Levels/Curves cannot be used locally without masks because they do not recognize the local context. Fortunately, some tools are now available to improve local contrast (Photoshop’s Shadow/Highlight tool, Akvis Enhancer, and Photomatix Tone Mapping).
Why do I use Akvis Enhancer and Photomatix, and not simply Photoshop with some masking? Because both tools use algorithms that currently are not found in Photoshop (some high-radius/ low-amount sharpening can achieve some of the same effect, however). While Tone Mapping is designed for high dynamic range images (HDR), Akvis Enhancer is the only tool I know of that is designed for local-contrast enhancements through finding color- contrast transitions.
A real-world example
As Figure 1 demonstrates, I often start with a very soft image from the RAW converter (in this case Adobe Photoshop Lightroom) with no clipped high- lights and as few clipped shadows as possible. I also don’t sharpen in the RAW converter.
It is much easier to enhance the contrast than to tone the contrast down (you need to work in 16-bit if you don’t want to risk posterization). If you have lost smooth transitions in high-contrast images, you cannot bring them back, but it is no problem to make smooth gradients more contrasty. Most areas in this photo are in the shade, but there are some very delicate backlit areas. To bring such images to life, I usually use either the Photomatix Tone Mapping or Akvis Enhancer plugin within Photoshop; this time I used both.
I began with Photomatix Tone Mapping, using the settings in Figure 4. This plugin works very well on some images and not so well on others. Setting the parameters is a bit of a trial-and-error process; with experience it gets much faster. (Note: Photomatix is normally used with HDR, or high dynamic-range images, but the local-contrast-enhancement filter often works well on normal 16-bit images.) I created a new layer for each plugin, and checked Photoshop’s histogram all the time to avoid any highlight clipping. After using Photomatix Tone Mapping on this image, I did end up with some clipped highlights. That is why I created a layer mask in Photoshop that excluded the highlights from the Tone Mapping result. The image now looked like Figure 5 (I’m showing a detail to make it easier to spot the subtle differences).
I could have continued with further processing, but wanted to pull out some more local contrast with the Akvis Enhancer Photoshop plugin (Mac and PC). This tool works magic on many images. The company claims it improves the contrast at color transitions. Be aware that Enhancer can also pull out a lot of noise. I often prevent this by using masks for skies and other homogeneous areas.
• Level of Detail: Five is the default value, which I use most of the time. This slide also can amplify noise (noise looks like detail to it). My sample image was taken with the Canon 1Ds Mk. II at ISO 400, and shows some noise, but I don’t think it shows in print even at 20 inches wide. In this scene, it is hard to tell what is noise and what is the detail in the rocks.
• Lightness: Controls the brightness of the resulting image. The default value is 50.
• Shadows: Opens up the shadows. The default value is 0.
• Highlights: Extracts more detail in the highlights. I often also use a low amount to avoid blowing out the highlights. The default value is 0.
Note: Enhancer does not seem to be properly color managed. This doesn’t bother me a lot as I know the useful settings by now.
I always use Akvis Enhancer on a new layer. If you switch between the start image and the result from Enhancer, you will be surprised how much more detail the image reveals. Enhancer has a tendency to blow out some of the highlights and clip some shadows. I used a mid- tone mask on the Enhancer layer to protect the shadows and highlights. Because I already did a previous contrast adjustment in Photomatix, I toned down the opacity of this layer to about 33% (very much a matter of taste). Figure 7 shows what the image looked like at this point.
I then adjusted the global contrast using the new Photoshop CS3 tool that combines Levels and Curves functionality (Figure 8). I also improved the saturation a bit. I used an interesting technique: adding a linear Curves adjustment layer; changing the Blend mode to Soft Light; then toning down opacity to taste (I settled on 40%). The image now has much more life (Figure 9).
Now it was time for some subtler fine tuning. I won’t cover these steps in detail but here is what I needed to do:
- Slightly tone down the somewhat aggressive highlights
- Sharpen for the details (your sharpening tool of choice)
- Slightly open up the darker shadow
- Selectively enhance the saturation of the red rocks using Photoshop’s Hue-Saturation tool
- Change the saturation and brightness of the greens with Photoshop’s Hue/ Saturation tool
This resulted in the final image shown in Figure 10, which used all the layers shown in Figure 11.
I hope I have demonstrated that an intelligent application of local contrast and some other enhancements can bring a low-contrast image to life.