Exposure Verification and Correction

The ColorChecker Passport provides a convenient, robust solution to color correction in the field. Without a visual reference, it can be a challenge to judge, control and edit images for the best highligh and shadow detail. It’s also hard to tell what your selective edits will do globally in other color regions. The Creative Enhancement target provides a visual 1/3 stop gray ramp to control shadow and highlight clipping.

The Creative Enhancement target is a collection of 8 patches that are designed to warn photographers of an exposure problem. The patches are separated into two groups: light and dark. The light patches are ordered with 1/3 of an F-stop difference between them. The dark patches are ordered the same, with the exception of the last patch; which represents the blackest patch in the ColorChecker target. The exposure difference between the darkest and next darkest patch is roughly 1/10th of a stop. The dynamic range of the target is roughly 32:1, or 5 stops.

So what does this all mean? First and foremost, every patch should be visibly different in the final reproduction, or there is something wrong with the workflow. The most typical problem is over-exposure. In this case, the two whitest patches may not be visually different. In other cases, the shadows will lose detail. This is a very typical issue in an sRGB workflow when the camera or color management system sets the black point to a theoretical number rather than physical black point in the scene.

Identifying Clipping
Clipping can be a photographer's worst enemy. In a wedding portrait, it is important to capture the fine details of the dress. If the highlights are too bright, you will lose that detail, and the bride will surely notice. On the other hand, if you are shooting a dark product, such as a leather couch, it can be difficult to hold the fine shadow details that show the surface texture. This is where the power of Raw can save the day. Although it may appear from a preview that shadow or highlight details have been lost, it is possible that the processing software just clipped them and they are still available in the Raw file. With some careful adjustments, you may be able to bring them back. However, once the details get clipped in a JPG or TIFF file, they are gone forever.

Not all clipping is bad. For instance, you may want to throw something in silhouette for creative reasons. That would require clipping. Similarly, when shooting very shiny objects like chrome or jewelry, you probably want to clip the “specular” highlights for a pure, bright, shiny white appearance.

If you set your white balance with the neutral gray target, you can use the exposure verification patches on the Raw Enhancement target to fine-tune your highlights and shadows.

• Sample the black patch with the eyedropper. This patch should be nearly neutral, so the R, G and B values should be close to equal. Although the black patch is very dark, it should not read as pure black.
• Do the same thing with the white point. The white square should be very light, but not pure white; and the RGB values should be nearly equal.
• To check for color cast, select the gray patches in the middle. Red, green and blue values should not vary from each other more than seven points on a 0-255 scale, or three points on a 0-100% scale.

Highlight Clipping Correction
The Highlight Clipping patches can help verify whether you are holding details in the highlights and shadows. In Adobe applications, use these patches along with the histogram to see if you are losing detail. Here’s how to do this in Lightroom and Camera Raw.

• In the Histogram window, click on the triangles in the corners to turn on the clipping preview for the shadow and highlight areas.
• Roll over the patches to check for blown out highlights. There should be a difference in value from one patch to the next, and none of the values should be at 255 or 100%.

While editing an image, settings like brightness, exposure and contrast can affect these values. If after adjusting these settings you notice you have lost some highlight detail, try using the Recovery tool to darken the highlight without darkening the rest of the image. If these adjustments do not bring back the highlight details, the shot was probably too over-exposed and cannot be recovered.

Shadow Clipping Correction
Use the Shadow Clipping patches to verify whether you are holding details in the shadows. We will look at how it is done in Lightroom and Camera Raw.

• In the Histogram window, click on the triangles in the corners to turn on the clipping preview for the shadow and highlight areas.
• Roll over the patches to check for clipping. There should be a difference in value from one patch to the next, and none of the values should be at 0.

Again, editing brightness, exposure, blacks and contrast can affect these values. You may be able to open up shadow details with the Fill Light tool, which will lighten mostly in the shadow areas. If you unable to bring back the details, the shot was probably too under-exposed.