Exposure Evaluation

Exposure Evaluation panel

Located in the Capture inspector, the histogram in the Exposure Evaluation panel displays individual Red, Blue, Green and Luminance channels for the captured image, which can be either RAW, TIFF or JPEG data depending on the image selected in the browser.

With RAW files, the histogram displays the data exactly as captured after the addition of a tone curve (that can be altered from the Base Charecteristics tool), the importance of which can’t be exaggerated when evaluating the optimal exposure. With the exception of white balance, no other settings applied or adjustments made in Capture One affect the histogram.

This is not the same as the histogram on the back of your typical camera that displays the values after the application of various image parameters and conversion to JPEG, using a smaller color space.

About the exposure meter

Beneath the histogram is a bar-type exposure meter that displays a safe working exposure range in green from -1.7 stops to +2 stops along with the selected image’s deviation from the averaged exposure (0). The red area indicates overexposure and potential clipping of highlights, taking into account the extra data in tonal range available from RAW files, compared with JPEG or TIFF files. At the other end of the scale is a gray area that warns of underexposure and potential clipping of data in the shadows.

While under-exposing is a common method to preserve highlights, subsequent adjustment in Capture One using the Exposure slider, for example, to shift the histogram to the right, is likely to reveal "shot" noise in the shadow regions and deepest blacks. This can reveal itself as a regular pattern or banding in some cases, that can be difficult to remove entirely without adversely affecting detail.  

The meter is meant as visual aid when working with a tethered camera, but it is also useful retrospectively, when determining the characteristics of your own camera’s sensor. 

 

Determining optimal exposure with RAW files

As there’s less tonal information captured in the deepest shadows by a linear recording device such as a sensor, it is beneficial to overexpose at the time of capture ensuring as many pixels saturate as possible. Not only does this widen the range of tones captured but it also helps lessen noise and maximise color accuracy. Determining the optimal exposure for your camera, however, depends on the sensor’s dynamic range.

As a guide, you should ensure the histogram is as close to the right hand side as possible without any of the channels touching or displaying a spike against the edge or wall of the panel. In addition, note the histogram’s meter value located below. Sensors with the best dynamic range will tolerate the most overexposure, however, it is still expected that the optimal exposure for the majority of modern cameras will fall between ±0 and +0.5 stops mark, depending on the sensor’s capabilities.

Note that testing of the sensor to determine its characteristics should be performed prior to any critical work. You can confirm the exposure using the histogram in the Histogram panel in the Exposure inspector - it should similarly be as as close to the right hand side as possible, without any of the channels displaying a spike against the edge or wall. If that’s the case decrease the exposure by using a higher shutter speed, or by closing down the aperture. 

Determining optimal exposure with RGB files

JPEG files are already processed to some degree, whether that’s out of the camera or from Capture One (or another, third-party editor) and therefore the histogram in the Exposure Evaluation panel is likely be no different to that found in the Histogram panel. TIFF files may also be previously processed. This can be confirmed by assessing the two histograms.