Operators |
fast_match — Searching all good matches of a template and an image.
fast_match(Image : Matches : TemplateID, MaxError : )
The operator fast_match performs a matching of the template of TemplateID and Image. Hereby the template will be moved over the points of Image so that the template always lies completely inside of Image. The matching criterion (“displaced frame difference”) is defined as follows:
SUMu,v {ABS { Image[row-u,col-v] - Template[u,v] }} error[row,col] = -----------------------------------------------------, AREA ( Template )
The difference between fast_match and exhaustive_match is that the matching for one position is stopped if the error is to high. This leads to a reduced runtime but one might miss correct matches. The runtime of the operator depends mainly on the size of the domain of Image. Therefore it is important to restrict the domain as far as possible, i.e. to apply the operator only in a very confined “region of interest”. The parameter MaxError determines the maximal error which the searched position is allowed to show. The lower this value is, the faster the operator runs.
All points which show a matching error smaller than MaxError will be returned in the output region Matches. This region can be used for further processing. For example by using a connection and best_match to find all the matching objects. If no point has a match error below MaxError the empty region (i.e no points) is returned.
Input image inside of which the pattern has to be found.
All points whose error lies below a certain threshold.
Template number.
Maximal average difference of the grayvalues.
Default value: 20.0
Suggested values: 0.0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 9.0, 11.0, 15.0, 17.0, 20.0, 30.0
Typical range of values: 0 ≤ MaxError ≤ 255
Minimum increment: 1
Recommended increment: 1
If the parameter values are correct, the operator fast_match returns the value 2 (H_MSG_TRUE). If the input is empty (no input images are available) the behaviour can be set via set_system('no_object_result',<Result>). If necessary, an exception is raised.
create_template, read_template, adapt_template, draw_region, draw_rectangle1, reduce_domain
best_match, best_match_mg, fast_match_mg, exhaustive_match, exhaustive_match_mg
Matching
Operators |