Bryson Leidich

Photography and Photoshop


Exposure Relativity

Most photographers do not deal with exposure in a precise way. The camera’s built-in meter and auto exposure serve the purpose in many cases and the photographer is free to react to the scene. This is a positive thing in many circumstances as you need to react to the scene rather than fuss with the camera. Unfortunately, it can lead to less than optimal exposures a little fussing up front can lead to better captures and less post processing angst. This is especially true when you do not have to react quickly to a changing scene which is typical when shooting landscapes.

Exposure is a relationship between the various tonal values in the image. The differences in reflectivity of areas of the scene is what creates the image and sets the mood of the photo. If the differences are great the image is said to have a high contrast and may require special consideration such as exposure bracketing,HDR or exposure blending to reign in the contrast. A subject with less inherent contrast will have a flat appearance coming out of the camera and may require expansion of the differences in tonal levels to look like you want it to.

This image was taken on the side of the road in Colorado. The lighting was fairly soft as a result of the cloud cover. Despite some high values in the sky area, the vast majority of the foreground was limited to the bottom half of the exposure scale. If you roll the mouse over the image you will see the original color capture before Photoshop adjustments. You will see how the wood structure is not rendered well and the sky contrast is rather flat as well.

Initial exposure was based on the high values in the sky, placing them as high as possible without clipping. An overall exposure based on the camera’s meter would have blown out the sky. I find that determining exposure based on the highest values works best for me. Once that is done the shadow areas are checked relative to the highlights.

I find that my camera typically wants to underexposure most average scenes by as much as a full stop, so I check the highlights and the overall histogram carefully after each capture. In addition I use spot metering to check specific areas of the image and "place" the values where I want them to be. This is an old technique known as the zone system.

In the zone system you use the meter to determine the exposure value of an area of the image. The meter tells you what the exposure should be if you want the area to be middle gray. You then modify the exposure in order to move the value up or down and expose according to the desired level. In the case of highlights you increase the exposure by about two stops depending on exactly how bright you want the area to record. That sets your exposure and the shadow values are recorded relative to the determined highlight exposure.

Setting the exposure based on the highlights seems to be to be the best option as clipped highlights and blank white areas are not what I want in my images. Second to that is the shadow area exposure which will be rendered in relation to the highlights. All that remains then is a quick check of the histogram to determine if the scene falls within the desired range and unimportant areas are not clipped at the bottom of the exposure. Losing highlight detail is not an option for me, while losing shadow detail is less important depending on the image but is easily remedied by a second exposure if needed,

The histogram confirmed that the scene was within the dynamic range of the camera, meaning the exposure I established for the sky did not force the shadows into clipping at the lower end. There was, in fact a substantial amount of foreground detail available and the left end of the histogram did not “hit the wall”. The gave me a good exposure for post processing with a single raw capture.

In post processing there was contrast added to the sky, which showed values from slightly below middle gray to the high 240s. There was also contrast added to the foreground, and in particular to the wood structure. In both cases the corrections were made using masks to limit the corrections to specific areas. Brightening the wood by raising the contrast in curves significantly increased the foreground interest and made the image come to life. The color version was interesting, but the image to me needed to be B&W. That conversion was pretty easy since the primary dynamic changes had been done in the color version, but final tweaks to the wood structure needed to be applied to the B&W version to get the real impact where it needed to be.