[Back to the Index]
The module allows augmentation of metadata by supplying the number of horizontal and vertical lines detected on an image of the reverse of an painting.
The module does not return the number of stretchers on the reverse image, only the number of horizontal and vertical lines. The number of stretchers may be equal to half this number, but that cannot be guaranteed.
| Module Speed | Very Slow (runs offline) |
| Module Accuracy | High |
The stretcher detector makes the assumption that the stretchers will manifest themselves as strong, straight lines within a reverse image. To this end, it attempts to find strong, straight lines with the use of the Hough transform for lines. This uses a similar technique to template matching, except the process is analytic, rather than exemplar, and returns results in a faster time.
The HT maps points in an edge image to lines in an accumulator space, and where there are peaks within the accumulator space there will be crossings of lines in the accumulator space, giving the two variables which define a line that exists in the image domain.
In reverse images, by our assumption, any lines which are detected in the edge image, are therefore edges to stretchers. A stretcher will generally have two edges (a left/top, and right/bottom edge) and generally the number of detected lines can be divided by two to retrieve the number of stretchers. Detection of a stretcher requires a more complex algorithm to determine which areas are wood (stretcher) and canvas.
Matching is simply the difference between the number of stretchers.