Better Light 7 manual Appendix B, Manipulating Exposure, Exposure Adjustments, Line Time

Appendix B

Manipulating Exposure

The Better Light digital camera system provides a very flexible set of controls for adjusting both exposure and processing. Most of these controls are directly analogous to their film photography namesakes, but several have not previously been readily available to the photographer, and none have provided the precision and consistency now available with this system. As with film, there are also some image quality trade-offs among these adjustments, and optimum ranges for each control.

Exposure Adjustments

Exposure changes are typically used for controlling under- or over-exposure conditions, and for equalizing the range of data values produced by each color channel (gray balancing). The primary rule of exposure, signal (density or data) = light x time is unchanged; less light requires more exposure time to produce the same signal level, whether it is a given density in a film image, or a given data value in a digital image. The amount of light is up to the photographer, and is a function of many variables, including the lens aperture setting. Exposure time is now controlled digitally; the shutter in the lens stays open during the entire imaging process. All three color channels of the CCD are controlled simultaneously by exposure time changes.

In addition to exposure time, the photographer now has the ability to independently adjust the effective sensitivity of each color channel of the CCD (its ISO rating) over a continuous range of more than four EV (f-stops), on a shot-by-shot basis. This powerful control allows precise gray bal- ancing of image data with nearly any continuous light source, and provides a wide range of effective ISO settings for increased flexibility in setting an exposure.

Finally, the Tone Curves can be used to “push” or “pull” a given exposure without significantly affecting contrast or color rendition. This function of the Tone Curves, while not strictly speaking an exposure adjustment, will be treated separately from Tone adjustments, which do affect contrast and color.

Line Time

This setting is equivalent to the shutter speed setting on a film camera. It controls the amount of time that each line of the image is exposed; adjustable in 1/3 EV (f-stop) increments. Longer line times provide increased absorption of light but can also increase scan times significantly. Longer line times also produce more dark current, which can increase shadow noise.

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