BIO RAD iCycler iQ Packing List And Installation Manual page 15

image.
Fig. 6.2. iQ configuration window with a calibration plate image and the expose image dialog box.
6. From the tool bar at the top of the Image dialog box, select Tools, then select Zoom.
Click with the left mouse button on the calibration plate image to increase the size of the
image; click with the right mouse button to reduce the size of the image. Usually two left
clicks of the mouse button increases the image to a size sufficient to adjust the mask.
Increase the size of the Image dialog box to fill most of the window using the sizing
function at the bottom right corner of the Image dialog box. Use the scroll bars to center
the image.
7. To turn off the zoom feature, select Tools from the Image dialog box menu bar, then
deselect Zoom.
6.2 Set the DC Offset
The DC offset controls the camera bias and affects the intensity of each pixel. When the
DC offset is set properly, you can place the cursor on points in the dark area, surrounding
the image of the 96-well plate, and the pixel values will be in the range of 40–70 counts.
You can check the pixel intensity by looking at the bar at the top of the image: the X and Y
coordinates of the cursor are displayed along with the intensity (I) of the pixel underneath
the cursor.
You can also assess the setting of the DC offset (bias) from the Gain box. The Gain box
presents the distribution of the pixel intensity in a histogram with intensity ranging from 0 to
1023, bottom to top. The White line at the top shows the white level (1023 counts) and the
Black line at the bottom shows the black (0 counts) level. The width of the
histogram correlates with the number of pixels at each level. There is always a large peak
very near the black line at the bottom of the Gain box. The goal of adjusting the DC
offset is to set it so that the black line cuts across the histogram about 1/3 of the way down the
large peak. See the figures below:
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