create_ocr_class_svmT_create_ocr_class_svmcreate_ocr_class_svmCreateOcrClassSvmCreateOcrClassSvm (Operator)

Name

create_ocr_class_svmT_create_ocr_class_svmcreate_ocr_class_svmCreateOcrClassSvmCreateOcrClassSvm — Create an OCR classifier using a support vector machine.

Signature

Description

create_ocr_class_svmcreate_ocr_class_svmcreate_ocr_class_svmCreateOcrClassSvmCreateOcrClassSvm creates an OCR classifier that uses a support vector machine (SVM). The handle of the OCR classifier is returned in OCRHandleOCRHandleOCRHandleOCRHandleOCRHandle.

For a description on how an SVM works, see create_class_svmcreate_class_svmcreate_class_svmCreateClassSvmCreateClassSvm. create_ocr_class_svmcreate_ocr_class_svmcreate_ocr_class_svmCreateOcrClassSvmCreateOcrClassSvm creates an SVM for classification with the classification mode given by ModeModeModeModemode. The length of the feature vector of the SVM (NumFeatures in create_class_svmcreate_class_svmcreate_class_svmCreateClassSvmCreateClassSvm) is determined from the features that are used for the OCR, which are passed in FeaturesFeaturesFeaturesFeaturesfeatures. The features are described below. The kernel is parameterized with KernelTypeKernelTypeKernelTypeKernelTypekernelType, KernelParamKernelParamKernelParamKernelParamkernelParam and NuNuNuNunu like in create_class_svmcreate_class_svmcreate_class_svmCreateClassSvmCreateClassSvm. The number of classes of the SVM (NumClasses in create_class_svmcreate_class_svmcreate_class_svmCreateClassSvmCreateClassSvm) is determined from the names of the characters to be used in the OCR, which are passed in CharactersCharactersCharactersCharacterscharacters. As described with create_class_svmcreate_class_svmcreate_class_svmCreateClassSvmCreateClassSvm, the parameters PreprocessingPreprocessingPreprocessingPreprocessingpreprocessing and NumComponentsNumComponentsNumComponentsNumComponentsnumComponents can be used to specify a preprocessing of the data (i.e., the feature vectors). For the sake of numerical stability, PreprocessingPreprocessingPreprocessingPreprocessingpreprocessing can typically be set to 'normalization'"normalization""normalization""normalization""normalization". In order to speed up classification time, 'principal_components'"principal_components""principal_components""principal_components""principal_components" or 'canonical_variates'"canonical_variates""canonical_variates""canonical_variates""canonical_variates" can be used, as the number of input features can be significantly reduced without deterioration of the recognition rate.

The features to be used for the classification are determined by FeaturesFeaturesFeaturesFeaturesfeatures. FeaturesFeaturesFeaturesFeaturesfeatures can contain a tuple of feature names. Each of these feature names results in one or more features to be calculated for the classifier. Some of the feature names compute gray value features (e.g., 'pixel_invar'"pixel_invar""pixel_invar""pixel_invar""pixel_invar"). Because a classifier requires a constant number of features (input variables), a character to be classified is transformed to a standard size, which is determined by WidthCharacterWidthCharacterWidthCharacterWidthCharacterwidthCharacter and HeightCharacterHeightCharacterHeightCharacterHeightCharacterheightCharacter. The interpolation to be used for the transformation is determined by InterpolationInterpolationInterpolationInterpolationinterpolation. It has the same meaning as in affine_trans_imageaffine_trans_imageaffine_trans_imageAffineTransImageAffineTransImage. The interpolation should be chosen such that no aliasing effects occur in the transformation. For most applications, InterpolationInterpolationInterpolationInterpolationinterpolation = 'constant'"constant""constant""constant""constant" should be used. It should be noted that the size of the transformed character is not chosen too large, because the generalization properties of the classifier may become bad for large sizes. In particular, for large sizes small segmentation errors will have a large influence on the computed features if gray value features are used. This happens because segmentation errors will change the smallest enclosing rectangle of the regions, thus the character is zoomed differently than the characters in the training set. In most applications, sizes between 6x8 and 10x14 should be used.

The parameter FeaturesFeaturesFeaturesFeaturesfeatures can contain the following feature names for the classification of the characters.

'default'"default""default""default""default"

'ratio'"ratio""ratio""ratio""ratio" and 'pixel_invar'"pixel_invar""pixel_invar""pixel_invar""pixel_invar" are selected.

'pixel'"pixel""pixel""pixel""pixel"

Gray values of the character (WidthCharacterWidthCharacterWidthCharacterWidthCharacterwidthCharacter x HeightCharacterHeightCharacterHeightCharacterHeightCharacterheightCharacter features).

'pixel_invar'"pixel_invar""pixel_invar""pixel_invar""pixel_invar"

Gray values of the character with maximum scaling of the gray values (WidthCharacterWidthCharacterWidthCharacterWidthCharacterwidthCharacter x HeightCharacterHeightCharacterHeightCharacterHeightCharacterheightCharacter features).

'pixel_binary'"pixel_binary""pixel_binary""pixel_binary""pixel_binary"

Region of the character as a binary image zoomed to a size of WidthCharacterWidthCharacterWidthCharacterWidthCharacterwidthCharacter x HeightCharacterHeightCharacterHeightCharacterHeightCharacterheightCharacter (WidthCharacterWidthCharacterWidthCharacterWidthCharacterwidthCharacter x HeightCharacterHeightCharacterHeightCharacterHeightCharacterheightCharacter features).

'gradient_8dir'"gradient_8dir""gradient_8dir""gradient_8dir""gradient_8dir"

Gradients are computed on the character image. The gradient directions are discretized into 8 directions. The amplitude image is decomposed into 8 channels according to these discretized directions. 25 samples on a 5x5 grid are extracted from each channel. These samples are used as features (200 features).

'projection_horizontal'"projection_horizontal""projection_horizontal""projection_horizontal""projection_horizontal"

Horizontal projection of the gray values (see gray_projectionsgray_projectionsgray_projectionsGrayProjectionsGrayProjections, HeightCharacterHeightCharacterHeightCharacterHeightCharacterheightCharacter features).

'projection_horizontal_invar'"projection_horizontal_invar""projection_horizontal_invar""projection_horizontal_invar""projection_horizontal_invar"

Maximally scaled horizontal projection of the gray values (HeightCharacterHeightCharacterHeightCharacterHeightCharacterheightCharacter features).

'projection_vertical'"projection_vertical""projection_vertical""projection_vertical""projection_vertical"

Vertical projection of the gray values (see gray_projectionsgray_projectionsgray_projectionsGrayProjectionsGrayProjections, WidthCharacterWidthCharacterWidthCharacterWidthCharacterwidthCharacter features).

'projection_vertical_invar'"projection_vertical_invar""projection_vertical_invar""projection_vertical_invar""projection_vertical_invar"

Maximally scaled vertical projection of the gray values (WidthCharacterWidthCharacterWidthCharacterWidthCharacterwidthCharacter features).

'ratio'"ratio""ratio""ratio""ratio"

Aspect ratio of the character (1 feature).

'anisometry'"anisometry""anisometry""anisometry""anisometry"

Anisometry of the character (see eccentricityeccentricityeccentricityEccentricityEccentricity, 1 feature).

'width'"width""width""width""width"

Width of the character before scaling the character to the standard size (not scale-invariant, see smallest_rectangle1smallest_rectangle1smallest_rectangle1SmallestRectangle1SmallestRectangle1, 1 feature).

'height'"height""height""height""height"

Height of the character before scaling the character to the standard size (not scale-invariant, see smallest_rectangle1smallest_rectangle1smallest_rectangle1SmallestRectangle1SmallestRectangle1, 1 feature).

'zoom_factor'"zoom_factor""zoom_factor""zoom_factor""zoom_factor"

Difference in size between the character and the values of WidthCharacterWidthCharacterWidthCharacterWidthCharacterwidthCharacter and HeightCharacterHeightCharacterHeightCharacterHeightCharacterheightCharacter (not scale-invariant, 1 feature).

'foreground'"foreground""foreground""foreground""foreground"

Fraction of pixels in the foreground (1 feature).

'foreground_grid_9'"foreground_grid_9""foreground_grid_9""foreground_grid_9""foreground_grid_9"

Fraction of pixels in the foreground in a 3x3 grid within the smallest enclosing rectangle of the character (9 features).

'foreground_grid_16'"foreground_grid_16""foreground_grid_16""foreground_grid_16""foreground_grid_16"

Fraction of pixels in the foreground in a 4x4 grid within the smallest enclosing rectangle of the character (16 features).

'compactness'"compactness""compactness""compactness""compactness"

Compactness of the character (see compactnesscompactnesscompactnessCompactnessCompactness, 1 feature).

'convexity'"convexity""convexity""convexity""convexity"

Convexity of the character (see convexityconvexityconvexityConvexityConvexity, 1 feature).

'moments_region_2nd_invar'"moments_region_2nd_invar""moments_region_2nd_invar""moments_region_2nd_invar""moments_region_2nd_invar"

Normalized 2nd moments of the character (see moments_region_2nd_invarmoments_region_2nd_invarmoments_region_2nd_invarMomentsRegion2ndInvarMomentsRegion2ndInvar, 3 features).

'moments_region_2nd_rel_invar'"moments_region_2nd_rel_invar""moments_region_2nd_rel_invar""moments_region_2nd_rel_invar""moments_region_2nd_rel_invar"

Normalized 2nd relative moments of the character (see moments_region_2nd_rel_invarmoments_region_2nd_rel_invarmoments_region_2nd_rel_invarMomentsRegion2ndRelInvarMomentsRegion2ndRelInvar, 2 features).

'moments_region_3rd_invar'"moments_region_3rd_invar""moments_region_3rd_invar""moments_region_3rd_invar""moments_region_3rd_invar"

Normalized 3rd moments of the character (see moments_region_3rd_invarmoments_region_3rd_invarmoments_region_3rd_invarMomentsRegion3rdInvarMomentsRegion3rdInvar, 4 features).

'moments_central'"moments_central""moments_central""moments_central""moments_central"

Normalized central moments of the character (see moments_region_centralmoments_region_centralmoments_region_centralMomentsRegionCentralMomentsRegionCentral, 4 features).

'moments_gray_plane'"moments_gray_plane""moments_gray_plane""moments_gray_plane""moments_gray_plane"

Normalized gray value moments and the angle of the gray value plane (see moments_gray_planemoments_gray_planemoments_gray_planeMomentsGrayPlaneMomentsGrayPlane, 4 features).

'phi'"phi""phi""phi""phi"

Orientation (angle) of the character (see elliptic_axiselliptic_axiselliptic_axisEllipticAxisEllipticAxis, 1 feature).

'num_connect'"num_connect""num_connect""num_connect""num_connect"

Number of connected components (see connect_and_holesconnect_and_holesconnect_and_holesConnectAndHolesConnectAndHoles, 1 feature).

'num_holes'"num_holes""num_holes""num_holes""num_holes"

Number of holes (see connect_and_holesconnect_and_holesconnect_and_holesConnectAndHolesConnectAndHoles, 1 feature).

'cooc'"cooc""cooc""cooc""cooc"

Values of the binary cooccurrence matrix (see gen_cooc_matrixgen_cooc_matrixgen_cooc_matrixGenCoocMatrixGenCoocMatrix, 12 features).

'num_runs'"num_runs""num_runs""num_runs""num_runs"

Number of runs in the region normalized by the height (1 feature).

'chord_histo'"chord_histo""chord_histo""chord_histo""chord_histo"

Frequency of the runs per row (HeightCharacterHeightCharacterHeightCharacterHeightCharacterheightCharacter features).

After the classifier has been created, it is trained using trainf_ocr_class_svmtrainf_ocr_class_svmtrainf_ocr_class_svmTrainfOcrClassSvmTrainfOcrClassSvm. After this, the classifier can be saved using write_ocr_class_svmwrite_ocr_class_svmwrite_ocr_class_svmWriteOcrClassSvmWriteOcrClassSvm. Alternatively, the classifier can be used immediately after training to classify characters using do_ocr_single_class_svmdo_ocr_single_class_svmdo_ocr_single_class_svmDoOcrSingleClassSvmDoOcrSingleClassSvm or do_ocr_multi_class_svmdo_ocr_multi_class_svmdo_ocr_multi_class_svmDoOcrMultiClassSvmDoOcrMultiClassSvm.

A comparison of SVM and the multi-layer perceptron (MLP) (see create_ocr_class_mlpcreate_ocr_class_mlpcreate_ocr_class_mlpCreateOcrClassMlpCreateOcrClassMlp) typically shows that SVMs are generally faster at training, especially for huge training sets, and achieve slightly better recognition rates than MLPs. The MLP is faster at classification and should therefore be prefered in time critical applications. Please note that this guideline assumes optimal tuning of the parameters.

Parallelization

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

Parameters

Example (HDevelop)

read_image (Image, 'letters')
* Segment the image.
bin_threshold (Image, Region)
dilation_circle (Region, RegionDilation, 3.5)
connection (RegionDilation, ConnectedRegions)
intersection (ConnectedRegions, Region, RegionIntersection)
sort_region (RegionIntersection, Characters, 'character', 'true', 'row')
* Generate the training file.
count_obj (Characters, Number)
Classes := []
for J := 0 to 25 by 1
    Classes := [Classes,gen_tuple_const(20,chr(ord('a')+J))]
endfor
Classes := [Classes,gen_tuple_const(20,'.')]
write_ocr_trainf (Characters, Image, Classes, 'letters.trf')
* Generate and train the classifier.
read_ocr_trainf_names ('letters.trf', CharacterNames, CharacterCount)
create_ocr_class_svm (8, 10, 'constant', 'default', CharacterNames, \
                      'rbf', 0.01, 0.01, 'one-versus-all', \
                      'principal_components', 10, OCRHandle)
trainf_ocr_class_svm (OCRHandle, 'letters.trf', 0.001, 'default')
* Re-classify the characters in the image.
do_ocr_multi_class_svm (Characters, Image, OCRHandle, Class)
clear_ocr_class_svm (OCRHandle)

Result

If the parameters are valid the operator create_ocr_class_svmcreate_ocr_class_svmcreate_ocr_class_svmCreateOcrClassSvmCreateOcrClassSvm returns the value 2 (H_MSG_TRUE). If necessary, an exception is raised.

Possible Successors

trainf_ocr_class_svmtrainf_ocr_class_svmtrainf_ocr_class_svmTrainfOcrClassSvmTrainfOcrClassSvm

Alternatives

create_ocr_class_mlpcreate_ocr_class_mlpcreate_ocr_class_mlpCreateOcrClassMlpCreateOcrClassMlp, create_ocr_class_boxcreate_ocr_class_boxcreate_ocr_class_boxCreateOcrClassBoxCreateOcrClassBox

See also

do_ocr_single_class_svmdo_ocr_single_class_svmdo_ocr_single_class_svmDoOcrSingleClassSvmDoOcrSingleClassSvm, do_ocr_multi_class_svmdo_ocr_multi_class_svmdo_ocr_multi_class_svmDoOcrMultiClassSvmDoOcrMultiClassSvm, clear_ocr_class_svmclear_ocr_class_svmclear_ocr_class_svmClearOcrClassSvmClearOcrClassSvm, create_class_svmcreate_class_svmcreate_class_svmCreateClassSvmCreateClassSvm, train_class_svmtrain_class_svmtrain_class_svmTrainClassSvmTrainClassSvm, classify_class_svmclassify_class_svmclassify_class_svmClassifyClassSvmClassifyClassSvm

Module

OCR/OCV