Filter
Top Products
Chapter 15 Menus and Dialog Boxes 289
Offset:
The Offset adjustment allows precise adjustment of the image brightness by
enabling counts to be subtracted from every data point in the image. The higher
the offset setting, the larger the values that are subtracted and the darker the
image becomes. Offset subtraction can be used to bring off-scale (clipped)
values into the gray-scale range. Where the result of the offset subtraction is zero
or negative, the darkest video level (black) is displayed. Note that active data-
acquisition must be in progress to see the effect of changing the Offset setting.
The offset setting range is 0 to 3812 counts. The offset is non-linear, with the
increment size varying from a low of 2 at the low (left) end to a high of 256 at
the high (right) end.
Together, the Gain and Offset dials are used to obtain the best possible video
image. The following technique frequently gives good results.
➧ Begin with a Scaling setting of 0 to 4096 and an Offset setting of 2
(minimum).
➧ Decrease the Scaling setting to where the displayed image is one click too
bright.
➧ Increase the Offset setting as required to darken the image and obtain the
most pleasing image display.
Scaling
Setting Mapping
0 to 4096 Data in entire A/D range (0 to 4095) are mapped to gray-scale.
0 to 2048 A/D data from 0 to 2047 (after offset subtraction) are mapped.
Higher values are clipped to 2047 (white).
0 to 1024 A/D data from 0 to 1023 (after offset subtraction) are mapped.
Higher values are clipped to 1023 (white).
0 to 512 A/D data from 0 to 511 (after offset subtraction) are mapped.
Higher values are clipped to 511 (white).
0 to 256 A/D data from 0 to 255 (after offset subtraction) are mapped.
Higher values are clipped to 255 (white).
0 to 128 A/D data from 0 to 127 (after offset subtraction) are mapped.
Higher values are clipped to 127 (white).
0 to 64 A/D data from 0 to 63 (after offset subtraction) are mapped.
Higher values are clipped to 63 (white).
Table 1.
Video mapping
vs. scaling
setting.