Finds the k best matches for each descriptor from a query set

matches = matcher.knnMatch(queryDescriptors, trainDescriptors, k)
matches = matcher.knnMatch(queryDescriptors, k)
[...] = matcher.knnMatch(..., 'OptionName', optionValue, ...)

Input

• queryDescriptors Query set of descriptors.
• trainDescriptors Train set of descriptors. This set is not added to the train descriptors collection stored in the class object.
• k Count of best matches found per each query descriptor or less if a query descriptor has less than k possible matches in total.

Output

• matches Matches. Each matches{i} is k or less matches for the same query descriptor. A cell array of length size(queryDescriptors,1), each cell is a 1-by-(k or less) structure array that has the following fields:
  • queryIdx query descriptor index (zero-based index)
  • trainIdx train descriptor index (zero-based index)
  • imgIdx train image index (zero-based index)
  • distance distance between descriptors (scalar)

Options

• Mask default empty
  • In the first form, mask specifying permissible matches between an input query and train matrices of descriptors. Matrix of size [size(queryDescriptors,1),size(trainDescriptors,1)].
  • In the second form, set of masks. Each masks{i} specifies permissible matches between the input query descriptors and stored train descriptors from the i-th image trainDescCollection{i}. Cell array of length length(trainDescriptors), each a matrix of size [size(queryDescriptors,1),size(trainDescriptors{i},1)].
• CompactResult Parameter used when the mask (or masks) is not empty. If CompactResult is false, the matches vector has the same size as queryDescriptors rows. If CompactResult is true, the matches vector does not contain matches for fully masked-out query descriptors. default false

This extended variant of cv.DescriptorMatcher.match() method finds several best matches for each query descriptor. The matches are returned in the distance increasing order. See cv.DescriptorMatcher.match() for the details about query and train descriptors.