create_ncc_modelT_create_ncc_modelCreateNccModelCreateNccModelcreate_ncc_model (Operator)

Name

create_ncc_modelT_create_ncc_modelCreateNccModelCreateNccModelcreate_ncc_model — Prepare an NCC model for matching.

Signature

Description

The operator create_ncc_modelcreate_ncc_modelCreateNccModelCreateNccModelCreateNccModelcreate_ncc_model prepares a template, which is passed in the image TemplateTemplateTemplateTemplatetemplatetemplate, as an NCC model used for matching using the normalized cross correlation (NCC). The ROI of the model is passed as the domain of TemplateTemplateTemplateTemplatetemplatetemplate.

The model is generated using multiple image pyramid levels at multiple rotations on each level and is stored in memory. The output parameter ModelIDModelIDModelIDModelIDmodelIDmodel_id is a handle for this model, which is used in subsequent calls to find_ncc_modelfind_ncc_modelFindNccModelFindNccModelFindNccModelfind_ncc_model.

The number of pyramid levels is determined with the parameter NumLevelsNumLevelsNumLevelsNumLevelsnumLevelsnum_levels. It should be chosen as large as possible because by this the time necessary to find the object is significantly reduced. On the other hand, NumLevelsNumLevelsNumLevelsNumLevelsnumLevelsnum_levels must be chosen such that the model is still recognizable and contains a sufficient number of points (at least eight) on the highest pyramid level. This can be checked using the domains of the output images of gen_gauss_pyramidgen_gauss_pyramidGenGaussPyramidGenGaussPyramidGenGaussPyramidgen_gauss_pyramid. If not enough model points are generated, the number of pyramid levels is reduced internally until enough model points are found on the highest pyramid level. If this procedure would lead to a model with no pyramid levels, i.e., if the number of model points is already too small on the lowest pyramid level, create_ncc_modelcreate_ncc_modelCreateNccModelCreateNccModelCreateNccModelcreate_ncc_model returns an error message. If NumLevelsNumLevelsNumLevelsNumLevelsnumLevelsnum_levels is set to 'auto'"auto""auto""auto""auto""auto" or 0, create_ncc_modelcreate_ncc_modelCreateNccModelCreateNccModelCreateNccModelcreate_ncc_model determines the number of pyramid levels automatically. The automatically computed number of pyramid levels can be queried using get_ncc_model_paramsget_ncc_model_paramsGetNccModelParamsGetNccModelParamsGetNccModelParamsget_ncc_model_params. In rare cases, it might happen that create_ncc_modelcreate_ncc_modelCreateNccModelCreateNccModelCreateNccModelcreate_ncc_model determines a value for the number of pyramid levels that is too large or too small. If the number of pyramid levels is chosen too large, the model may not be recognized in the image or it may be necessary to select very low parameters for MinScoreMinScoreMinScoreMinScoreminScoremin_score in find_ncc_modelfind_ncc_modelFindNccModelFindNccModelFindNccModelfind_ncc_model in order to find the model. If the number of pyramid levels is chosen too small, the time required to find the model in find_ncc_modelfind_ncc_modelFindNccModelFindNccModelFindNccModelfind_ncc_model may increase. In these cases, the number of pyramid levels should be selected by inspecting the output of gen_gauss_pyramidgen_gauss_pyramidGenGaussPyramidGenGaussPyramidGenGaussPyramidgen_gauss_pyramid. Here, ModeModeModeModemodemode = 'constant'"constant""constant""constant""constant""constant" and ScaleScaleScaleScalescalescale = 0.5 should be used.

The parameters AngleStartAngleStartAngleStartAngleStartangleStartangle_start and AngleExtentAngleExtentAngleExtentAngleExtentangleExtentangle_extent determine the range of possible rotations, in which the model can occur in the image. Note that the model can only be found in this range of angles by find_ncc_modelfind_ncc_modelFindNccModelFindNccModelFindNccModelfind_ncc_model. The parameter AngleStepAngleStepAngleStepAngleStepangleStepangle_step determines the step length within the selected range of angles. Hence, if subpixel accuracy is not specified in find_ncc_modelfind_ncc_modelFindNccModelFindNccModelFindNccModelfind_ncc_model, this parameter specifies the accuracy that is achievable for the angles in find_ncc_modelfind_ncc_modelFindNccModelFindNccModelFindNccModelfind_ncc_model. AngleStepAngleStepAngleStepAngleStepangleStepangle_step should be chosen based on the size of the object. Smaller models do not possess many different discrete rotations in the image, and hence AngleStepAngleStepAngleStepAngleStepangleStepangle_step should be chosen larger for smaller models. If AngleExtentAngleExtentAngleExtentAngleExtentangleExtentangle_extent is not an integer multiple of AngleStepAngleStepAngleStepAngleStepangleStepangle_step, AngleStepAngleStepAngleStepAngleStepangleStepangle_step is modified accordingly. To ensure a sampling of the range of possible rotations that is independent of the given AngleStartAngleStartAngleStartAngleStartangleStartangle_start, the range of possible rotations is modified as follows: If there is no positive integer value n such that AngleStartAngleStartAngleStartAngleStartangleStartangle_start plus n times AngleStepAngleStepAngleStepAngleStepangleStepangle_step is exactly 0.0, AngleStartAngleStartAngleStartAngleStartangleStartangle_start is decreased by up to AngleStepAngleStepAngleStepAngleStepangleStepangle_step and AngleExtentAngleExtentAngleExtentAngleExtentangleExtentangle_extent is increased by AngleStepAngleStepAngleStepAngleStepangleStepangle_step.

The model is pre-generated for the selected angle range and stored in memory. The memory required to store the model is proportional to the number of angle steps and the number of points in the model. Hence, if AngleStepAngleStepAngleStepAngleStepangleStepangle_step is too small or AngleExtentAngleExtentAngleExtentAngleExtentangleExtentangle_extent too big, it may happen that the model no longer fits into the (virtual) memory. In this case, either AngleStepAngleStepAngleStepAngleStepangleStepangle_step must be enlarged or AngleExtentAngleExtentAngleExtentAngleExtentangleExtentangle_extent must be reduced. In any case, it is desirable that the model completely fits into the main memory, because this avoids paging by the operating system, and hence the time to find the object will be much smaller. Since angles can be determined with subpixel resolution by find_ncc_modelfind_ncc_modelFindNccModelFindNccModelFindNccModelfind_ncc_model, AngleStepAngleStepAngleStepAngleStepangleStepangle_step >= 1 can be selected for models of a diameter smaller than about 200 pixels. If AngleStepAngleStepAngleStepAngleStepangleStepangle_step = 'auto'"auto""auto""auto""auto""auto" or 0 is selected, create_ncc_modelcreate_ncc_modelCreateNccModelCreateNccModelCreateNccModelcreate_ncc_model automatically determines a suitable angle step length based on the size of the model. The automatically computed angle step length can be queried using get_ncc_model_paramsget_ncc_model_paramsGetNccModelParamsGetNccModelParamsGetNccModelParamsget_ncc_model_params.

The parameter MetricMetricMetricMetricmetricmetric determines the conditions under which the model is recognized in the image. If MetricMetricMetricMetricmetricmetric = 'use_polarity'"use_polarity""use_polarity""use_polarity""use_polarity""use_polarity", the object in the image and the model must have the same contrast. If, for example, the model is a bright object on a dark background, the object is found only if it is also brighter than the background. If MetricMetricMetricMetricmetricmetric = 'ignore_global_polarity'"ignore_global_polarity""ignore_global_polarity""ignore_global_polarity""ignore_global_polarity""ignore_global_polarity", the object is found in the image also if the contrast reverses globally. In the above example, the object hence is also found if it is darker than the background. The runtime of find_ncc_modelfind_ncc_modelFindNccModelFindNccModelFindNccModelfind_ncc_model will increase slightly in this case.

The center of gravity of the domain (region) of the model image TemplateTemplateTemplateTemplatetemplatetemplate is used as the origin (reference point) of the model. A different origin can be set with set_ncc_model_originset_ncc_model_originSetNccModelOriginSetNccModelOriginSetNccModelOriginset_ncc_model_origin.

Execution Information

• Multithreading type: reentrant (runs in parallel with non-exclusive operators).
• Multithreading scope: global (may be called from any thread).
• Processed without parallelization.

This operator returns a handle. Note that the state of an instance of this handle type may be changed by specific operators even though the handle is used as an input parameter by those operators.

Parameters

Result

If the parameters are valid, the operator create_ncc_modelcreate_ncc_modelCreateNccModelCreateNccModelCreateNccModelcreate_ncc_model returns the value 2 ( H_MSG_TRUE) . If the parameter NumLevelsNumLevelsNumLevelsNumLevelsnumLevelsnum_levels are chosen such that the model contains too few points, the error 8506 is raised.

Possible Predecessors

draw_regiondraw_regionDrawRegionDrawRegionDrawRegiondraw_region, reduce_domainreduce_domainReduceDomainReduceDomainReduceDomainreduce_domain, thresholdthresholdThresholdThresholdThresholdthreshold

Possible Successors

find_ncc_modelfind_ncc_modelFindNccModelFindNccModelFindNccModelfind_ncc_model, get_ncc_model_paramsget_ncc_model_paramsGetNccModelParamsGetNccModelParamsGetNccModelParamsget_ncc_model_params, clear_ncc_modelclear_ncc_modelClearNccModelClearNccModelClearNccModelclear_ncc_model, write_ncc_modelwrite_ncc_modelWriteNccModelWriteNccModelWriteNccModelwrite_ncc_model, set_ncc_model_originset_ncc_model_originSetNccModelOriginSetNccModelOriginSetNccModelOriginset_ncc_model_origin, set_ncc_model_paramset_ncc_model_paramSetNccModelParamSetNccModelParamSetNccModelParamset_ncc_model_param, find_ncc_modelsfind_ncc_modelsFindNccModelsFindNccModelsFindNccModelsfind_ncc_models

Alternatives

create_generic_shape_modelcreate_generic_shape_modelCreateGenericShapeModelCreateGenericShapeModelCreateGenericShapeModelcreate_generic_shape_model

Module

Matching