Automatic Point Detection

Automatic point detection is a feature for digitizing surfaces. If many feature points look similar on a surface, users need only mark one point. Photo4D can try to detect other similar points. This is done using the Detect subpage in the Mark page of the Main Window.

Setup auto-detection

The basic steps involved in auto-mark detection are the following:

1. Select a working image: image in which Photo4D is to detect feature points.
2. Select a current point in the working image: Photo4D searches for points that are similar to the current point when scanning the working image. The current point is used as a reference point and should closely match the points to be detected. It should be marked accurately using the MagGlass.
3. Select a detection area: use Control-left mouse button to drag a rectangle. Photo4D will detect marks inside.
4. Setup detection parameters: This includes selecting proper values for the following fields: Number of points, Score threshold, and Overlapping threshold. The "Use color" checkbutton should also be set properly. If it is unchecked, the program won't search for dots of the same color. The reason we sometimes don't use color is that we want to detect dots that have different colors compared to the reference mark. When setting up detection parameters, users may make a rough estimation of how many feature points appears in the detection area and enter it as the value in the "Number of points" field. This number does not need to be accurate. The value of the "Score threshold" is generally around 0.5~0.8, depending on how similar the feature points are. The value of the "Overlapping threshold" should be smaller than the minimum distance, in pixels, between two feature points.
5. Enter a proper value for the mask size.
6. Start detection: Press the "Detect marks" button to begin the auto- detect process.

If the image contains different types of feature points, the above process may be repeated for each type.

It is unlikely that all marks will be detected or positioned correctly. Some dots may not be marked at all and some marks might be placed in totally unexpected positions. Therefore, manual editing is usually required to complete marking.