Mitsubishi P91DW User Manual download pdf (Page 106)

Chapter 5: Analysis Tools

5-5

The values are the average pixel values within the object, adjusted to a scale of 0 to 100.

(0 corresponding to black pixel values, and 100 corresponding to white pixel values.)

If both a center and an outer circle have been specified, two values are displayed. The

upper value corresponds to the inner circle and the lower value corresponds to the torus.

The INVERT Box

The INVERT function reverses the relative density assignments so that 0 corresponds to

white and 100 corresponds to black. If the image has dark areas of interest on a light

background, then INVERT should be selected by placing an “X” in its box. (If the image

has light areas of interest on a dark background, the INVERT option should not be

activated.) Unlike the REVERSE button described in Chapter 3, this function does not

alter the appearance of the image.

Removing Background using the Scan Blank Function

Since a microtiter plate is not completely transparent, it contributes to the density

measured when samples are scanned. A non-uniform light source also affects the density

measured. To ensure that the density measured is attributable only to the sample in the

wells, scan a “blank” before scanning samples.

Load an image of a clean, unused microtiter plate and align the objects as described

above. Once the array has been set up, click on the Scan Blank button. The average

pixel gray value for each object (and torus) is measured and set to zero (0).

Now, when samples are scanned, the gray value of the blank is subtracted from that of the

sample before it is scaled. This ensures that the density reported only reflects the sample

in each well.

When Scan Blank has been selected, the background values obtained apply to all

subsequent scans. To indicate that a background is being applied, the Scan Blank button

changes to read Clear Blank. To turn off this background subtraction function, simply

click on Clear Blank.

Outputting Data

The Output button outputs data as a hard copy or as an ASCII text file which can then be

imported into a spreadsheet for further analysis and/or graphing.

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Mitsubishi P91DW User Manual Page 106