Retouching Digital Images
White Balance Settings Panel
The White Balance settings panel, available as a tabbed dialog box through the Retouch Image window panel tab header, is utilized to adjust the overall tonal balance of digital images captured with the DXM 1200 camera system.
A typical adjustment for white balance in digital photomicrography is illustrated in Figure 1 (a & b), where the specimen is a multiply-stained thin section of a pine tree stem. On the left (Figure 1(a)) is a digital image of the thin section before white balance adjustment. Note that the overall color tones are dark and "muddy" and the background is a light gray in color. After selection of an appropriate area (one of the clear areas in the upper central portion of the image) and application of white balance adjustment algorithms (Figure 1(b)), the image appears more natural with a greater range of tonal values and a white background.
White balance of the camera system can be controlled through the Live settings panel for images prior to acquisition, but there is no comparable control for black balance. Compensation of a digital image for both black and white balance can ensure sharp and crisp photomicrographs with excellent overall tonal qualities. The ability to adjust black balance is often useful in fluorescence photomicrography where background fluorescence can produce a lack of contrast in digital images, such as illustrated in Figure 1(c). The specimen is a culture of bovine pulmonary arterial cells that have been fixed and stained with multiple fluorochromes. When imaged with a filter combination that has bandpass wavelengths for several dyes, light backgrounds are a common problem and can lead to a dramatic reduction in image contrast. Utilizing the black balance feature in the Retouch Image settings panel, the black balance value can be established (Figure 1(d)), leading to much sharper images with jet black backgrounds and a significant improvement in overall image contrast.
Illustrated in Figure 2 is the Retouch Image window White Balance settings panel. To operate the panel, click on either the white eyedropper (white balance) or black eyedropper (black balance) to launch the software utility. Prior to choosing the eyedropper, determine whether balance should be calculated using a single pixel or a rectangular area by clicking on the appropriate radio button in the Sampling Area Selection menu. When either the black or white eyedropper button is clicked and the mouse cursor is moved over the image window, it turns into a miniature eyedropper icon. The pointed end of the eyedropper can be utilized to select an individual pixel or draw a rectangular marquee from which the pixel sampling can take place. The next step is to click on the Start button to launch the algorithm that calculates white or black balance. Only one balance setting can be performed at a time.
Interactive Java Tutorial
Retouch Image Window
Explore the various features available in the DXM 1200 ACT-1 image correction and retouching software. Included are algorithms for brightness, contrast, color correction, cropping, and resizing images.
When the image meets approval, click on the OK button located at the bottom of the Retouch Image window to apply the changes and return to the ACT-1 software window. The image should then be saved with a different name by the Save As command line from the File main menu. If one of the correction factors is changed and the user switches to another settings panel, the Retouch Image dialog box (not illustrated) appears to question whether or not to apply the update. Clicking on the OK button will apply the changes, while clicking on the Cancel button in this dialog box will cancel the latest corrections. Note that clicking on the Apply button in any Retouch Image settings panel will apply the changes and reset the correction factors back to zero.
Although the ACT-1 control software Retouch Image feature is not as fully developed as high-end image editors such as Adobe Photoshop, the algorithms for white and black balance appear to work in a satisfactory manner. We recommend the utilization of more sophisticated image editors for critical work, but for routine microscopy, the White Balance settings panel will produce acceptable images.
