SFRplus – Selecting regions based on Center-to-corner distance

November 17, 2012
December 17, 2014

Some customers need to select regions based on specified center-to-corner distance. The objective of this is to match up the test region to to the lens specifications.

Imatest Master allows one to view the exact center-to-corner distance of each region in the Multi-ROI summary, shown below, using the Display ctr-corner % only setting (lower right).

It’s very important to note that the center-to-corner % distance of an edge is proportional to the bar-bar height % (the top of the top bar – the bottom of the bottom bar in % of the image height) for an image with a fixed aspect ratio (3:2 for the above image, shown just to the right of (WxH).

For example, the Edge 3_2_R (Column 3, Row 2 (relative to the center), Right edge) is always 82.1/89.6 = 0.9163 of the bat-to-bar height.

Another example, let’s say that we want the two edges on the lower-right be located at an average distance of 70% of the center-to-corner distance. The current average is (81.9+83.8)/2 = 82.85%. The image would have to be framed (by backing away from it or using a smaller chart) so the bar-to-bar height was 89.6*70/82.85 = 75.7% (of the image height).

Another option is available if you can’t get the exact distances. The squares in rows 2 and 4 can be shifted slightly to the left or right of their nominal positions. This does not require a change in the software. (This cannot be done with rows 1, 3, and 5 without affecting the vertical convergence angle measurement.).

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