Color Photography Assignment: Exposing to the Right

There are some slight differences from the Exposed To The Right and the standard metering images: More detail in the ETTR.

Here is some useful information:

If you have learned the basics of how a digital camera operates and some information on what RAW files are and how to use Adobe Camera Raw (ACR) to process them. A more in-depth understanding of how to use ACR will allow you to get the most out of RAW files you already have.  There is a step that comes before the portion of RAW file workflow. This step is exposing a RAW file to get the best possible quality out of the final image. To do this, we must learn new habits of metering and making exposure decisions that are different than anything used for film or JPEG capture.

The goal of previous metering techniques was placing the tones in the captured image where the photographer wanted them to be, based on a subjective interpretation of the scene. In other words, if something is grey in the scene, it should be grey in the photograph. And if it is black in the scene, it should be black in the photograph. This exposure strategy still works for RAW files, and high-quality results can be obtained when using it.

However, there is another strategy that, when used properly, results in richer colors and an effective increase in dynamic range. This is called "expose to the right," or ETTR for short. It is based on a deeper understanding of how digital cameras capture and process data. The histogram is the key to successful use of ETTR.

Imagine that we are working with a sensor that has a dynamic range of five stops. This is a safe bet, as most RAW files taken by a DSLR come from a sensor that has a dynamic range of at least five stops. This sensor takes a picture and the histogram from that image is displayed on the camera's LCD. 

Due to the fact that digital sensors, both CMOS and CCD are linear capture devices, 50% of the data they capture is placed into the first stop of dynamic range (represented by Stop 1). 25% is in the next stop, 12.5% in the stop after that and so on down to the last stop that contains 3.125% of the sensor's potential ability to record information. In this picture, 50% of the potential data is unused.

Digital capture is a binary world. Anything that does not have a value of one must have a value of zero. If there is no actual data in that part of the histogram, the in-camera processing compensates for this by filling the space with zeros. These zeros are the digital equivalent of radio static.

There are observable results of signal-to-noise ratio (SNR). In the case of radio, the signal is the music and the noise is the static. A high SNR in radio gives you music with little or no static. A low SNR gives you lots of static and very little music. In digital capture, there are two places where SNR comes into play. The first is the initial exposure stage. The second is related to ISO. 

A low SNR in a digital file will give you higher contrast, higher noise, less accurate color, and a loss of detail, especially in the shadows. A high SNR will give you just the opposite. The resulting images from a file that has a high SNR will have more detail throughout the image, accurate color, less noise, and lower contrast. The combination of lower contrast and more shadow detail extends the usable dynamic range of the camera's sensor. 

This image has a much higher SNR, and will therefore have higher quality across the board. It is using the first stop of dynamic range to capture the bulk of the detail in the image.

The goal of ETTR is to capture the maximum possible amount of data in the file. Photos that were shot using this strategy will require more work in ACR than photos shot with the standard exposure strategy. Using ETTR also effectively lowers the sensors ISO, because it requires longer shutter speeds or large apertures to let in the additional light required to move the histogram to the right. However, if the intent of the photographer is to produce the maximum possible quality, then these minor drawbacks are well worth it. If the intent is to rapidly deliver a file to a situation where speed of arrival is more important than ultimate quality, then the standard exposure strategy is the best choice. 

An image that was exposed using ETTR will always look far too bright, with low saturation and washed-out color. This is normal. Adding contrast and saturation does not harm such an image. Turning up the blacks in ACR and turning down the exposure (the two most common adjustments made to an ETTR image) have the added benefit of reducing noise.

In order to use ETTR properly, the photographer must pay even more careful attention to the camera and to contrast ratio measurement. Even though we are trying to maximize data by moving the histogram to the right, regardless of the actual tone, we still cannot clip our highlights. Once highlight detail is lost, it is gone forever. It is also important to get to know your particular camera. Some camera models have a much higher tolerance for exposures above the suggested reading than others. More expensive, pro-level cameras are more likely to be able to tolerate overexposure than the less expensive entry-level cameras.

Here are the assignment details:

Choose a subject where shadow detail is important to properly represent what you would like us to see about the subject.

Shoot five different scenes, with two images of each scene. The five different scenes should be related either formally or conceptually.

For each scene, shoot one shot exposed using standard metering techniques and one shot using ETTR. They should be identically framed, so don't forget to use a tripod.