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Device Settings How is camera white balance calibrated?
Device Settings

Information in this article applies to:

  • uScope Navigator V4.0 and Later

Article ID: NDS1170 — Created: 31 Mar 2018 — Reviewed: 27 Jul 2020

Question

I have read that the auto-calibrate button for the Overview and Objective cameras performs a white balance and flat-field calibration. How does the white balance calibration work?

Answer

The white-balance calibration works by analyzing successive images from the camera at different illumination levels and calculating the best RGB adjustment values necessary to render a perfectly grey (unsaturated white) image.

Calibrating the Overview Camera...

When the auto-calibrate button is clicked for the overview camera, the uScope platform moves to the overview position and prompts you to remove any slide (or slide tray for uScopeDX and uScopeGX models) that may be in the unit. Once you confirm that the slide (or slide tray) is removed, the uScope Navigator software proceeds to calibrate the overview illuminator color balance (white balance) and subsequently capture an image to use for flat-field correction.

Calibrating the Objective Camera...

When the auto-calibrate button is clicked for an objective camera, the uScope platform moves to a calibration window (hole) in the slide tray and proceeds to calibrate the illuminator color balance (white balance) and subsequently capture an image to use for flat-field correction.

Camera Calibration Illumination Levels...

The following illumination levels are used to calibrate the uScope cameras. The illumination levels are a percentage of the maximum. The calibration level is set to 35% (for all but the uScopeGX) to provide greater illumination headroom (we assume that most users want to make the image brighter rather than darker).

uScope ModelOverview Camera
Calibration Illuminator Level
Objective Camera
Calibration Illuminator Level
uScopeMXII35%35%
uScopeHXII35%35%
uScopeDX35%35%
uScopeGX35%15%

During the white balance calibration, the uScope Navigator software adjusts the camera exposure (red, green, and blue levels) to achieve the digital equivalent of an 18% grey card. An 18% grey card is a standard tool used to calibrate film and motion picture cameras.

Note
The objective camera is calibrated in open air—not through the glass slide. As a result, some glass slides may introduce a slight color tint to the scanned images. If you need to correct the color of such scans, you may wish to consider using color correction filter settings. Refer to RGB Filter for more information.

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