Some customers need to select regions based on a specified center-to-corner distance. This can be done using an Edge ID file (enhanced to be an Edge ID/Zone selection file in Imatest 5.0+), which is available in SFRplus, eSFR ISO, and Checkerboard. The box below contains concise instructions for using these files.
A recent enhancement to Imatest Master 4.5 makes it easier to view the exact center-to-corner distance of each selected region in the Multi-ROI summary, shown below, using the Display ctr-corner % only setting in Imatest 4.5 (lower right).
For SFRplus, 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).
- The center-to-corner % distance of the edge is inversely proportional to the camera-to-chart distance.
For example, the Edge 3_2_R (Column 3, Row 2 (below the center), Right edge) is located at 74.8% of the center-to-corner distance. Moving the chart away from the camera reduces this number.
Another example (from a different image), 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.).