Type Mappings¶

This page documents how C++ OpenCV types map to Ruby classes.

Basic Types¶

C++	Ruby	Description
`cv::Mat`	`Cv::Mat`	N-dimensional dense array (images, matrices)
`cv::Scalar`	`Cv::Scalar`	4-element vector (colors, values)
`cv::Point`	`Cv::Point`	2D integer point
`cv::Point2f`	`Cv::Point2f`	2D float point
`cv::Point2d`	`Cv::Point2d`	2D double point
`cv::Point3i`	`Cv::Point3i`	3D integer point
`cv::Point3f`	`Cv::Point3f`	3D float point
`cv::Point3d`	`Cv::Point3d`	3D double point
`cv::Size`	`Cv::Size`	2D integer size (width, height)
`cv::Size2f`	`Cv::Size2f`	2D float size
`cv::Size2d`	`Cv::Size2d`	2D double size
`cv::Rect`	`Cv::Rect`	Integer rectangle (x, y, width, height)
`cv::Rect2f`	`Cv::Rect2f`	Float rectangle
`cv::Rect2d`	`Cv::Rect2d`	Double rectangle
`cv::Range`	`Cv::Range`	Integer range (start, end)
`cv::RotatedRect`	`Cv::RotatedRect`	Rotated rectangle
`cv::TermCriteria`	`Cv::TermCriteria`	Termination criteria for iterative algorithms
`cv::Moments`	`Cv::Moments`	Image moments

Vector Types¶

Small fixed-size vectors:

C++	Ruby	Description
`cv::Vec2b`	`Cv::Vec2b`	2 unsigned chars
`cv::Vec3b`	`Cv::Vec3b`	3 unsigned chars (BGR pixel)
`cv::Vec4b`	`Cv::Vec4b`	4 unsigned chars (BGRA pixel)
`cv::Vec2s`	`Cv::Vec2s`	2 shorts
`cv::Vec3s`	`Cv::Vec3s`	3 shorts
`cv::Vec4s`	`Cv::Vec4s`	4 shorts
`cv::Vec2i`	`Cv::Vec2i`	2 integers
`cv::Vec3i`	`Cv::Vec3i`	3 integers
`cv::Vec4i`	`Cv::Vec4i`	4 integers
`cv::Vec6i`	`Cv::Vec6i`	6 integers
`cv::Vec8i`	`Cv::Vec8i`	8 integers
`cv::Vec2f`	`Cv::Vec2f`	2 floats
`cv::Vec3f`	`Cv::Vec3f`	3 floats
`cv::Vec4f`	`Cv::Vec4f`	4 floats
`cv::Vec6f`	`Cv::Vec6f`	6 floats
`cv::Vec2d`	`Cv::Vec2d`	2 doubles
`cv::Vec3d`	`Cv::Vec3d`	3 doubles
`cv::Vec4d`	`Cv::Vec4d`	4 doubles

Typed Matrix Classes¶

Type-safe matrix templates:

C++	Ruby	Element Type
`cv::Mat1b`	`Cv::Mat1b`	1-channel unsigned char
`cv::Mat1s`	`Cv::Mat1s`	1-channel short
`cv::Mat1w`	`Cv::Mat1w`	1-channel unsigned short
`cv::Mat1i`	`Cv::Mat1i`	1-channel int
`cv::Mat1f`	`Cv::Mat1f`	1-channel float
`cv::Mat1d`	`Cv::Mat1d`	1-channel double
`cv::Mat2b`	`Cv::Mat2b`	2-channel unsigned char
`cv::Mat3b`	`Cv::Mat3b`	3-channel unsigned char (BGR image)
`cv::Mat4b`	`Cv::Mat4b`	4-channel unsigned char (BGRA image)
`cv::Mat3f`	`Cv::Mat3f`	3-channel float
...	...	(all combinations available)

Matrix Type Constants¶

Global constants for Mat type specification:

Constant	Meaning
`CV_8UC1`	8-bit unsigned, 1 channel
`CV_8UC3`	8-bit unsigned, 3 channels
`CV_8UC4`	8-bit unsigned, 4 channels
`CV_8SC1`	8-bit signed, 1 channel
`CV_16UC1`	16-bit unsigned, 1 channel
`CV_16SC1`	16-bit signed, 1 channel
`CV_32SC1`	32-bit signed integer, 1 channel
`CV_32FC1`	32-bit float, 1 channel
`CV_32FC2`	32-bit float, 2 channels
`CV_64FC1`	64-bit float (double), 1 channel

Pattern: CV_{depth}{signed}{channels} where: - Depth: 8, 16, 32, 64 - Signed: U (unsigned), S (signed), F (float) - Channels: C1, C2, C3, C4

STL Container Mappings¶

C++ STL containers map to Ruby Std:: classes:

C++	Ruby
`std::vector<cv::Mat>`	`Std::Vector≺cv꞉꞉Mat≻`
`std::vector<cv::Point>`	`Std::Vector≺cv꞉꞉Point_≺int≻≻`
`std::vector<cv::Point2f>`	`Std::Vector≺cv꞉꞉Point_≺float≻≻`
`std::vector<cv::KeyPoint>`	`Std::Vector≺cv꞉꞉KeyPoint≻`
`std::vector<cv::DMatch>`	`Std::Vector≺cv꞉꞉DMatch≻`
`std::vector<cv::Rect>`	`Std::Vector≺cv꞉꞉Rect_≺int≻≻`
`std::vector<int>`	`Std::Vector≺int≻`
`std::vector<float>`	`Std::Vector≺float≻`
`std::vector<double>`	`Std::Vector≺double≻`
`std::vector<uchar>`	`Std::Vector≺unsigned char≻`
`std::vector<std::vector<cv::Point>>`	`Std::Vector≺vector≺cv꞉꞉Point_≺int≻≻≻`
`std::string`	Ruby `String` (automatic conversion)

Note: Ruby uses special Unicode characters (≺, ≻, ꞉꞉) in type names.

Input/Output Array Types¶

C++	Ruby Method	Purpose
`cv::InputArray`	`mat.input_array`	Read-only input
`cv::OutputArray`	`mat.output_array`	Write-only output
`cv::InputOutputArray`	`mat.input_output_array`	Read-write

Smart Pointers¶

C++	Ruby
`cv::Ptr<T>`	`Cv::Ptr≺T≻` or just the class
`std::shared_ptr<T>`	`Std::SharedPtr≺T≻`

Most factory methods return smart pointers that Ruby handles automatically:

# These work equivalently
orb = Cv::ORB.create        # Returns Ptr<ORB>, usable directly
sift = Cv::SIFT.create(500) # Returns Ptr<SIFT>

Feature Detection Types¶

C++	Ruby
`cv::KeyPoint`	`Cv::KeyPoint`
`cv::DMatch`	`Cv::DMatch`
`cv::Feature2D`	`Cv::Feature2D`
`cv::DescriptorMatcher`	`Cv::DescriptorMatcher`

Algorithm Classes¶

C++	Ruby
`cv::Algorithm`	`Cv::Algorithm`
`cv::ORB`	`Cv::ORB`
`cv::SIFT`	`Cv::SIFT`
`cv::AKAZE`	`Cv::AKAZE`
`cv::BRISK`	`Cv::BRISK`
`cv::KAZE`	`Cv::KAZE`
`cv::CascadeClassifier`	`Cv::CascadeClassifier`
`cv::HOGDescriptor`	`Cv::HOGDescriptor`
`cv::BackgroundSubtractorMOG2`	`Cv::BackgroundSubtractorMOG2`
`cv::BackgroundSubtractorKNN`	`Cv::BackgroundSubtractorKNN`

DNN Types¶

C++	Ruby
`cv::dnn::Net`	`Cv::Dnn::Net`
`cv::dnn::Layer`	`Cv::Dnn::Layer`
`cv::dnn::Model`	`Cv::Dnn::Model`
`cv::dnn::ClassificationModel`	`Cv::Dnn::ClassificationModel`
`cv::dnn::DetectionModel`	`Cv::Dnn::DetectionModel`

Machine Learning Types¶

C++	Ruby
`cv::ml::StatModel`	`Cv::Ml::StatModel`
`cv::ml::SVM`	`Cv::Ml::SVM`
`cv::ml::DTrees`	`Cv::Ml::DTrees`
`cv::ml::RTrees`	`Cv::Ml::RTrees`
`cv::ml::Boost`	`Cv::Ml::Boost`
`cv::ml::KNearest`	`Cv::Ml::KNearest`
`cv::ml::ANN_MLP`	`Cv::Ml::ANN_MLP`
`cv::ml::TrainData`	`Cv::Ml::TrainData`

Video Types¶

C++	Ruby
`cv::VideoCapture`	`Cv::VideoCapture`
`cv::VideoWriter`	`Cv::VideoWriter`
`cv::Tracker`	`Cv::Tracker`
`cv::TrackerMIL`	`Cv::TrackerMIL`

Enum Naming Pattern¶

C++ enums map to Ruby enum classes:

C++	Ruby
`cv::IMREAD_*`	`Cv::ImreadModes::IMREAD_*`
`cv::IMWRITE_*`	`Cv::ImwriteFlags::IMWRITE_*`
`cv::COLOR_*`	`Cv::ColorConversionCodes::COLOR_*`
`cv::THRESH_*`	`Cv::ThresholdTypes::THRESH_*`
`cv::MORPH_*`	`Cv::MorphTypes::MORPH_*`
`cv::BORDER_*`	`Cv::BorderTypes::BORDER_*`
`cv::INTER_*`	`Cv::InterpolationFlags::INTER_*`
`cv::RETR_*`	`Cv::RetrievalModes::RETR_*`
`cv::CHAIN_APPROX_*`	`Cv::ContourApproximationModes::CHAIN_APPROX_*`
`cv::LINE_*`	`Cv::LineTypes::LINE_*`
`cv::FONT_*`	`Cv::HersheyFonts::FONT_*`

Introspecting Types¶

Use Ruby introspection to discover available types:

require 'opencv-ruby'

# List all classes in Cv module
Cv.constants.select { |c| Cv.const_get(c).is_a?(Class) }

# List methods on a class
Cv::Mat.instance_methods(false)

# List enum values
Cv::ImreadModes.constants

# Check class hierarchy
Cv::ORB.ancestors