How do I interpret a camera histogram for brightfield?

Video Tool Panels: Camera Histogram

If the live image on your screen does not match the one in your eyepieces, try to adjust the white balance.
If the live image matches the image in your eyepieces, examine the gray part of the camera histogram to assess the quality of the image.

Examples:

This is an ideal histogram for most types of brightfield data.

The dynamic range is nearly the entire range of the camera.

The dynamic range is too low.

Try to increase the exposure time until the histogram fills at least 2/3 of the histogram window.

To improve the dynamic range, you may move the white point slider to the left (see figure on the left).

This may give the illusion of a better image.

Most of the dynamic range is lost (see 2nd histogram) and the signal-to-noise ratio is lower.

Background image only

Good example for the acquisition of a brightfield background image -- Virtual Tissue (slide scanning): Acquiring a background Image (Brightfield)

Try to obtain a histogram as narrow and as much to the right as possible.
If you need to modify the exposure, do so before the acquisition.
- Control the exposure to avoid a saturated image.
- Do not to modify the exposure after the acquisition; this would result in removing signal instead of solely background noise.

This histogram indicates the presence of dust or other artifacts in the background image.

Make the proper adjustments to avoid the display of these artifacts in each tile of the acquired tissue. Virtual Tissue (slide scanning): Troubleshooting imaging issues (Brightfield) for suggestions.

The red line on the right of the graph indicates saturation. If the image is completely saturated, the function (represented in gray) is not visible; only the red line appears.

If enabled, Clip Detect will show most of the image as red.

To correct this, decrease the light level or exposure time until the dynamic range is nearly the entire range of the camera.

The blue line on the left indicates that the signal is below the range.

This histogram suggests that the light source is not sufficient the camera.

To correct this, examine an image in the eyepieces.

Try increasing the light level.
Open the shutters in the light path.
Switch the light path on the microscope to send light to the camera.
Verify that the exposure time is high enough, and that the gain is set correctly.
- For most cameras, the default gain is either 0, 1, or 255 and should not be adjusted for brightfield data.

The blue line on the left may not appear depending on the sensitivity of the camera.