ImageFlip C++ library

v1.0.3

Table of contents

• Overview
• Versions
• Library files
• ImageFlip class description
  • ImageFlip class declaration
  • getVersion method
  • initVFilter method
  • setParam method
  • getParam method
  • getParams method
  • executeCommand method
  • processFrame method
  • setMask method
  • encodeSetParamCommand method of VFilter class
  • encodeCommand method of VFilter class
  • decodeCommand method of VFilter class
  • decodeAndExecuteCommand method
• Data structures
  • VFilterCommand enum
  • VFilterParam enum
• VFilterParams class description
  • VFilterParams class declaration
  • Serialize VFilter params
  • Deserialize VFilter params
  • Read params from JSON file and write to JSON file
• Build and connect to your project
• Example

Overview

ImageFlip C++ library implements simple image flip function based on OpenCV and compatible with VFilter interface to be implemented in video processing pipelines. The library supports left-right, up-down and left-right-up-down image flip. The library depends on VFilter library (provides interface for video filter, source code included, Apache 2.0 license) and OpenCV library (version >= 4.5, linked, Apache 2.0 license). The library uses C++17 standard.

Versions

Table 1 - Library versions.

Version	Release date	What’s new
1.0.0	27.02.2024	First version of the library.
1.0.1	24.03.2024	- Submodules updated. - Documentation updated.
1.0.2	21.05.2024	- Submodules updated. - Documentation updated.
1.0.3	23.07.2024	- Update CMake structure.

Library files

The library is supplied as source code only. The user is provided with a set of files in the form of a CMake project (repository). The repository structure is shown below:

CMakeLists.txt ------------- Main CMake file of the library.
3rdparty ------------------- Folder with third-party libraries.
    CMakeLists.txt --------- CMake file to include third-party libraries.
    VFilter ---------------- Folder with VFilter library source code.
src ------------------------ Folder with source code of the library.
    CMakeLists.txt --------- CMake file of the library.
    ImageFlip.cpp ---------- SC++ implementation file.
    ImageFlip.h ------------ Header file which includes ImageFlip class declaration.
    ImageFlipVersion.h ----- Header file which includes version of the library.
    ImageFlipVersion.h.in -- CMake service file to generate version file.
test ----------------------- Folder for test application.
    CMakeLists.txt --------- CMake file for test application.
    main.cpp --------------- Source code file of test application.

ImageFlip class description

ImageFlip class declaration

The ImageFlip class declared in ImageFlip.h file. Class declaration:

namespace cr
{
namespace video
{
class ImageFlip : public VFilter
{
public:

    /// Get the version of the ImageFlip class.
    static std::string getVersion();

    /// Initialize image flip.
    bool initVFilter(VFilterParams& params) override;

    /// Set VFilter parameter.
    bool setParam(VFilterParam id, float value) override;

    /// Get the value of a specific VFilter parameter.
    float getParam(VFilterParam id) override;

    /// Get the structure containing all VFilter parameters.
    void getParams(VFilterParams& params) override;

    /// Execute a VFilter action command.
    bool executeCommand(VFilterCommand id) override;

    /// Process frame.
    bool processFrame(cr::video::Frame& frame) override;

    /// Set mask for filter.
    bool setMask(cr::video::Frame mask) override;

    /// Decode and execute command.
    bool decodeAndExecuteCommand(uint8_t* data, int size) override;
};
}
}

getVersion method

The getVersion() static method returns string of current class version. Method declaration:

static std::string getVersion();

Method can be used without ImageFlip class instance:

std::cout << "ImageFlip version: " << cr::video::ImageFlip::getVersion();

Console output:

ImageFlip version: 1.0.3

initVFilter method

The initVFilter(…) method initializes image flip. Method uses only parameter mode from VFilterParams class. Method declaration:

bool initVFilter(VFilterParams& params) override;

Parameter	Value
params	VFilterParams class object. Method uses only parameter mode from VFilterParams class. Mode: 0 - Off. 1 - Left-Right. 2 - Up-Down. 3 - Both.

Returns: TRUE if the video filter initialized or FALSE if not.

setParam method

The setParam (…) method sets new parameters value. The library provides thread-safe setParam(…) method call. This means that the setParam(…) method can be safely called from any thread. Method declaration:

bool setParam(VFilterParam id, float value) override;

Parameter	Description
id	Parameter ID according to VFilterParam enum. Method supports only parameters: MODE. Mode: 0 - Off. 1 - Left-Right. 2 - Up-Down. 3 - Both.
value	Mode value.

Returns: TRUE if the parameter was set or FALSE if not.

getParam method

The getParam(…) method returns parameter value. The library provides thread-safe getParam(…) method call. This means that the getParam(…) method can be safely called from any thread. Method declaration:

float getParam(VFilterParam id) override;

Parameter	Description
id	Parameter ID according to VFilterParam enum. Method supports only parameters: MODE and PROCESSING_TIME_MCSEC. For other parameters the method will return -1.

Returns: parameter value or -1 if the parameters doesn’t exist (not supported in particular implementation).

getParams method

The getParams(…) method is designed to obtain all image flip params. The library provides thread-safe getParams(…) method call. This means that the getParams(…) method can be safely called from any thread. Method declaration:

void getParams(VFilterParams& params) override;

Parameter	Description
params	Reference to VFilterParams object to store params. Method will fill parameters: mode and processingTimeMcSec. Other parameters will be set to -1.0.

executeCommand method

The executeCommand(…) method executes video filter action command. Not supported by ImageFlip class. Method declaration:

bool executeCommand(VFilterCommand id) override;

Parameter	Description
id	Command ID according to VFilterCommand enum. Not supported by ImageFlip class.

Returns: TRUE if the command executed or FALSE if not.

processFrame method

The processFrame(…) method designed to process frame (image flip). The library provides thread-safe processFrame(…) method call. This means that the processFrame(…) method can be safely called from any thread. Method declaration:

bool processFrame(cr::video::Frame& frame) override;

Parameter	Description
frame	Reference to Frame object.

Returns: TRUE if frame processed (image flip) or FALSE if not. If filter disabled the method will return TRUE without video frame processing.

setMask method

The setMask(…) method designed to set video filter mask. Not supported by ImageFlip class. Method declaration:

bool setMask(cr::video::Frame mask) override;

Parameter	Description
mask	Filter mask in form of Frame object with GRAY pixel format. Mask not supported by ImageFlip class.

Returns: TRUE in any cases.

encodeSetParamCommand method of VFilter class

The encodeSetParamCommand(…) static method encodes command to change any VFilter parameter value. To control any video filter remotely, the developer has to design his own protocol and according to it encode the command and deliver it over the communication channel. To simplify this, the VFilter class contains static methods for encoding the control command. The VFilter class provides two types of commands: a parameter change command (SET_PARAM) and an action command (COMMAND). encodeSetParamCommand(…) designed to encode SET_PARAM command. Method declaration:

static void encodeSetParamCommand(uint8_t* data, int& size, VFilterParam id, float value);

Parameter	Description
data	Pointer to data buffer for encoded command. Must have size >= 11.
size	Size of encoded data. Will be 11 bytes.
id	Parameter ID according to VFilterParam enum.
value	Parameter value.

encodeSetParamCommand(…) is static and used without VFilter class instance. This method used on client side (control system). Command encoding example:

// Buffer for encoded data.
uint8_t data[11];
// Size of encoded data.
int size = 0;
// Random parameter value.
float outValue = static_cast<float>(rand() % 20);
// Encode command.
VFilter::encodeSetParamCommand(data, size, VFilterParam::LEVEL, outValue);

encodeCommand method of VFilter class

The encodeCommand(…) static method encodes command for VFilter remote control. To control any video filter remotely, the developer has to design his own protocol and according to it encode the command and deliver it over the communication channel. To simplify this, the VFilter class contains static methods for encoding the control command. The VFilter class provides two types of commands: a parameter change command (SET_PARAM) and an action command (COMMAND). encodeCommand(…) designed to encode COMMAND command (action command). Method declaration:

static void encodeCommand(uint8_t* data, int& size, VFilterCommand id);

Parameter	Description
data	Pointer to data buffer for encoded command. Must have size >= 7.
size	Size of encoded data. Will be 7 bytes.
id	Command ID according to VFilterCommand enum.

encodeCommand(…) is static and used without VFilter class instance. This method used on client side (control system). Command encoding example:

// Buffer for encoded data.
uint8_t data[7];
// Size of encoded data.
int size = 0;
// Encode command.
VFilter::encodeCommand(data, size, VFilterCommand::RESTART);

decodeCommand method of VFilter class

The decodeCommand(…) static method decodes command on image filter side. Method declaration:

static int decodeCommand(uint8_t* data, int size, VFilterParam& paramId, VFilterCommand& commandId, float& value);

Parameter	Description
data	Pointer to input command.
size	Size of command. Must be 11 bytes for SET_PARAM and 7 bytes for COMMAND.
paramId	VFilter parameter ID according to VFilterParam enum. After decoding SET_PARAM command the method will return parameter ID.
commandId	VFilter command ID according to VFilterCommand enum. After decoding COMMAND the method will return command ID.
value	VFilter parameter value (after decoding SET_PARAM command).

Returns: 0 - in case decoding COMMAND, 1 - in case decoding SET_PARAM command or -1 in case errors.

decodeAndExecuteCommand method

The decodeAndExecuteCommand(…) method decodes and executes command encoded by encodeSetParamCommand(…) and encodeCommand(…) methods on video filter side. The library provides thread-safe decodeAndExecuteCommand(…) method call. This means that the decodeAndExecuteCommand(…) method can be safely called from any thread. Method declaration:

bool decodeAndExecuteCommand(uint8_t* data, int size) override;

Parameter	Description
data	Pointer to input command.
size	Size of command. Must be 11 bytes for SET_PARAM or 7 bytes for COMMAND.

Returns: TRUE if command decoded (SET_PARAM or COMMAND) and executed (action command or set param command).

Data structures

VFilterCommand enum

Enum declaration:

enum class VFilterCommand
{
    /// Reset image filter algorithm.
    RESET = 1,
    /// Enable filter.
    ON,
    /// Disable filter.
    OFF
};

Table 2 - Action commands description.

Command	Description
RESET	Not supported by ImageFlip class.
ON	Not supported by ImageFlip class.
OFF	Not supported by ImageFlip class.

VFilterParam enum

Enum declaration:

enum class VFilterParam
{
	/// Current filter mode, usually 0 - off, 1 - on.
	MODE = 1,
	/// Enhancement level for particular filter, as a percentage in range from 
	/// 0% to 100%.
	LEVEL,
	/// Processing time in microseconds. Read only parameter.
	PROCESSING_TIME_MCSEC,
	/// Type of the filter. Depends on the implementation.
	TYPE,
	/// VFilter custom parameter. Custom parameters used when particular image 
	/// filter has specific unusual parameter.
	CUSTOM_1,
	/// VFilter custom parameter. Custom parameters used when particular image 
	/// filter has specific unusual parameter.
	CUSTOM_2,
	/// VFilter custom parameter. Custom parameters used when particular image 
	/// filter has specific unusual parameter.
	CUSTOM_3
};

Table 3 - Params description.

Parameter	Access	Description
MODE	read / write	Image flip mode: 0 - Off. 1 - Left-Right. 2 - Up-Down. 3 - Both.
LEVEL	read / write	Not supported by ImageFlip class.
PROCESSING_TIME_MCSEC	read only	Processing time in microseconds. Read only parameter. Used to check performance of image flip.
TYPE	read / write	Not supported by ImageFlip class.
CUSTOM_1	read / write	Not supported by ImageFlip class.
CUSTOM_2	read / write	Not supported by ImageFlip class.
CUSTOM_3	read / write	Not supported by ImageFlip class.

VFilterParams class description

VFilterParams class declaration

The VFilterParams class is used to provide video filter parameters structure. Also VFilterParams provides possibility to write/read params from JSON files (JSON_READABLE macro) and provides methods to encode and decode params. VFilterParams interface class declared in VFilter.h file. Class declaration:

class VFilterParams
{
public:
    /// Current filter mode, usually 0 - off, 1 - on.
    int mode{ 0 };
    /// Enhancement level for particular filter, as a percentage in range from 
    /// 0% to 100%.
    float level{ 0 };
    /// Processing time in microseconds. Read only parameter.
    int processingTimeMcSec{ 0 };
    /// Type of the filter. Depends on the implementation.
    int type{ 0 };
    /// VFilter custom parameter. Custom parameters used when particular image 
    /// filter has specific unusual parameter.
    float custom1{ 0.0f };
    /// VFilter custom parameter. Custom parameters used when particular image 
    /// filter has specific unusual parameter.
    float custom2{ 0.0f };
    /// VFilter custom parameter. Custom parameters used when particular image 
    /// filter has specific unusual parameter.
    float custom3{ 0.0f };

    /// Macro from ConfigReader to make params readable/writable from JSON.
    JSON_READABLE(VFilterParams, mode, level, type, custom1, custom2, custom3)

    /// operator =
    VFilterParams& operator= (const VFilterParams& src);

    // Encode (serialize) params.
    bool encode(uint8_t* data, int bufferSize, int& size,
                                             VFilterParamsMask* mask = nullptr);
	// Decode (deserialize) params.
    bool decode(uint8_t* data, int dataSize);
};

Table 4 - VFilterParams class fields description is related to VFilterParam enum description.

Field	type	Description
mode	int	Image flip mode: 0 - Off. 1 - Left-Right. 2 - Up-Down. 3 - Both.
level	float	Not supported by ImageFlip class.
processingTimeMcSec	int	Processing time in microseconds. Read only parameter. Used to check performance of image flip.
type	int	Not supported by ImageFlip class.
custom1	float	Not supported by ImageFlip class.
custom2	float	Not supported by ImageFlip class.
custom3	float	Not supported by ImageFlip class.

None: VFilterParams class fields listed in Table 4 have to reflect params set/get by methods setParam(…) and getParam(…).

Serialize VFilter params

VFilterParams class provides method encode(…) to serialize VFilter params. Serialization of VFilterParams is necessary in case when image filter parameters have to be sent via communication channels. Method provides options to exclude particular parameters from serialization. To do this method inserts binary mask (1 byte) where each bit represents particular parameter and decode(…) method recognizes it. Method declaration:

bool encode(uint8_t* data, int bufferSize, int& size, VFilterParamsMask* mask = nullptr);

Parameter	Value
data	Pointer to data buffer. Buffer size must be >= 48 bytes.
bufferSize	Data buffer size. Buffer size must be >= 48 bytes.
size	Size of encoded data.
mask	Parameters mask - pointer to VFilterParamsMask structure. VFilterParamsMask (declared in VFilter.h file) determines flags for each field (parameter) declared in VFilterParams class. If the user wants to exclude any parameters from serialization, he can put a pointer to the mask. If the user wants to exclude a particular parameter from serialization, he should set the corresponding flag in the VFilterParamsMask structure.

Returns: TRUE if params encoded (serialized) or FALSE if not.

VFilterParamsMask structure declaration:

struct VFilterParamsMask
{
    bool mode{ true };
    bool level{ true };
    bool processingTimeMcSec{ true };
    bool type{ true };
    bool custom1{ true };
    bool custom2{ true };
    bool custom3{ true };
};

Example without parameters mask:

// Prepare parameters.
cr::video::VFilterParams params;
params.level = 80.0f;

// Encode (serialize) params.
int bufferSize = 128;
uint8_t buffer[128];
int size = 0;
params.encode(buffer, bufferSize, size);

Example with parameters mask:

// Prepare parameters.
cr::video::VFilterParams params;
params.level = 80.0;

// Prepare mask.
cr::video::VFilterParams mask;
// Exclude level.
mask.level = false;

// Encode (serialize) params.
int bufferSize = 128;
uint8_t buffer[128];
int size = 0;
params1.encode(buffer, bufferSize, size, &mask);

Deserialize VFilter params

VFilterParams class provides method decode(…) to deserialize params. Deserialization of VFilterParams is necessary in case when it is needed to receive params via communication channels. Method automatically recognizes which parameters were serialized by encode(…) method. Method declaration:

bool decode(uint8_t* data, int dataSize);

Parameter	Value
data	Pointer to data buffer with serialized params.
dataSize	Size of command data.

Returns: TRUE if params decoded (deserialized) or FALSE if not.

Example:

// Prepare parameters.
cr::video::VFilterParams params1;
params1.level = 80;

// Encode (serialize) params.
int bufferSize = 128;
uint8_t buffer[128];
int size = 0;
params1.encode(buffer, bufferSize, size);

// Decode (deserialize) params.
cr::video::VFilterParams params2;
params2.decode(buffer, size);

Read params from JSON file and write to JSON file

VFilter depends on open source ConfigReader library which provides method to read params from JSON file and to write params to JSON file. Example of writing and reading params to JSON file:

// Write params to file.
cr::utils::ConfigReader inConfig;
cr::video::VFilterParams in;
inConfig.set(in, "vFilterParams");
inConfig.writeToFile("VFilterParams.json");

// Read params from file.
cr::utils::ConfigReader outConfig;
if(!outConfig.readFromFile("VFilterParams.json"))
{
    cout << "Can't open config file" << endl;
    return false;
}

VFilterParams.json will look like:

{
    "vFilterParams":
    {
        "level": 50,
        "mode": 2,
        "type": 1,
        "custom1": 0.7,
        "custom2": 12.0,
        "custom3": 0.61
    }
}

Build and connect to your project

Typical commands to build ImageFlip:

cd ImageFlip
mkdir build
cd build
cmake ..
make

If you want connect ImageFlip to your CMake project as source code you can make follow. For example, if your repository has structure:

CMakeLists.txt
src
    CMakeList.txt
    yourLib.h
    yourLib.cpp

Create folder 3rdparty in your repository and copy ImageFlip repository folder there. New structure of your repository:

CMakeLists.txt
src
    CMakeList.txt
    yourLib.h
    yourLib.cpp
3rdparty
    ImageFlip

Create CMakeLists.txt file in 3rdparty folder. CMakeLists.txt should contain:

cmake_minimum_required(VERSION 3.13)

################################################################################
## 3RD-PARTY
## dependencies for the project
################################################################################
project(3rdparty LANGUAGES CXX)

################################################################################
## SETTINGS
## basic 3rd-party settings before use
################################################################################
# To inherit the top-level architecture when the project is used as a submodule.
SET(PARENT ${PARENT}_YOUR_PROJECT_3RDPARTY)
# Disable self-overwriting of parameters inside included subdirectories.
SET(${PARENT}_SUBMODULE_CACHE_OVERWRITE OFF CACHE BOOL "" FORCE)

################################################################################
## CONFIGURATION
## 3rd-party submodules configuration
################################################################################
SET(${PARENT}_SUBMODULE_IMAGE_FLIP                      ON  CACHE BOOL "" FORCE)
if (${PARENT}_SUBMODULE_IMAGE_FLIP)
    SET(${PARENT}_IMAGE_FLIP                            ON  CACHE BOOL "" FORCE)
    SET(${PARENT}_IMAGE_FLIP_TEST                       OFF CACHE BOOL "" FORCE)
endif()

################################################################################
## INCLUDING SUBDIRECTORIES
## Adding subdirectories according to the 3rd-party configuration
################################################################################
if (${PARENT}_SUBMODULE_IMAGE_FLIP)
    add_subdirectory(ImageFlip)
endif()

File 3rdparty/CMakeLists.txt adds folder ImageFlip to your project and excludes test application from compiling (by default test applications and example are excluded from compiling if ImageFlip is included as sub-repository).The new structure of your repository:

CMakeLists.txt
src
    CMakeList.txt
    yourLib.h
    yourLib.cpp
3rdparty
    CMakeLists.txt
    ImageFlip

Next you need include folder 3rdparty in main CMakeLists.txt file of your repository. Add string at the end of your main CMakeLists.txt:

add_subdirectory(3rdparty)

Next you have to include ImageFlip library in your src/CMakeLists.txt file:

target_link_libraries(${PROJECT_NAME} ImageFlip)

Done!

Example

The example creates artificial image and provides user interface to control image flip mode:

#include <iostream>
#include <cstdint>
#include <string.h>
#include <opencv2/opencv.hpp>
#include "ImageFlip.h"

int main(void)
{
    std::cout << "ImageFlip v" <<
	cr::video::ImageFlip::getVersion() << std::endl;

	// Prepare source artificial image.
	const int width = 1280;
	const int height = 720;
	cv::Mat srcImg = cv::Mat::zeros(height, width, CV_8UC3);
	cr::video::Frame frame(width, height, cr::video::Fourcc::BGR24);
	cv::circle(srcImg, cv::Point(250, 250),
			   50, cv::Scalar(0, 0, 255), cv::FILLED, cv::LINE_AA);

	// Create image flip object and params.
	cr::video::ImageFlip imageFlip;
	cr::video::VFilterParams params;

    // Main loop.
    while (true)
    {
		// Copy source image data for Frame object.
		memcpy(frame.data, srcImg.data, frame.size);

		// Image flip.
		imageFlip.processFrame(frame);

		// Get image flip params (VFilterParams).
		imageFlip.getParams(params);

		// Draw params.
		cv::Mat resultImg(height, width, CV_8UC3, frame.data);
		std::string mode;
		switch (params.mode) {
		case 0: mode = "OFF"; break;
		case 1: mode = "LEFT-RIGHT"; break;
		case 2: mode = "UP-DOWN"; break;
		case 3: mode = "BOTH"; break;
		default: mode = "OFF"; break; }
		cv::putText(resultImg, "[1/2]Mode: " + mode,
                    cv::Point(5, 25), cv::FONT_HERSHEY_SIMPLEX, 0.7,
                    cv::Scalar(255, 255, 0), 1, cv::LINE_AA);
		cv::putText(resultImg, "Time, mcsec: " +
					std::to_string(params.processingTimeMcSec),
                    cv::Point(5, 50), cv::FONT_HERSHEY_SIMPLEX, 0.7,
                    cv::Scalar(255, 255, 0), 1, cv::LINE_AA);

		// Show results.
		cv::imshow("ImageFlip", resultImg);

		// Process keyboard events.
		switch (cv::waitKey(30))
		{
		case 27:
			return 1;
		case 49:
			imageFlip.setParam(cr::video::VFilterParam::MODE, params.mode - 1);
			break;
		case 50:
			imageFlip.setParam(cr::video::VFilterParam::MODE, params.mode + 1);
			break;
		}
    }
    return 1;
}

Example user interface: