OpenCV 5.0.0-pre
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OpenCV environment variables reference

Table of Contents

Prev Tutorial: OpenCV configuration options reference
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Introduction

OpenCV can change its behavior depending on the runtime environment:

  • enable extra debugging output or performance tracing
  • modify default locations and search paths
  • tune some algorithms or general behavior
  • enable or disable workarounds, safety features and optimizations

Notes:

  • ⭐ marks most popular variables
  • variables with names like this VAR_${NAME} describes family of variables, where ${NAME} should be changed to one of predefined values, e.g. VAR_TBB, VAR_OPENMP, ...

Setting environment variable in Windows

In terminal or cmd-file (bat-file):

set MY_ENV_VARIABLE=true
C:\my_app.exe

In GUI:

  • Go to "Settings -> System -> About"
  • Click on "Advanced system settings" in the right part
  • In new window click on the "Environment variables" button
  • Add an entry to the "User variables" list

Setting environment variable in Linux

In terminal or shell script:

export MY_ENV_VARIABLE=true
./my_app

or as a single command:

MY_ENV_VARIABLE=true ./my_app

Setting environment variable in Python

import os
os.environ["MY_ENV_VARIABLE"] = "True" # value must be a string
import cv2 # variables set after this may not have effect
Note
This method may not work on all operating systems and/or Python distributions. For example, it works on Ubuntu Linux with system Python interpreter, but doesn't work on Windows 10 with the official Python package. It depends on the ability of a process to change its own environment (OpenCV uses getenv from C++ runtime to read variables).
See also:

Types

  • bool - 1, True, true, TRUE / 0, False, false, FALSE
  • number/_size_ - unsigned number, suffixes MB, Mb, mb, KB, Kb, kb
  • string - plain string or can have a structure
  • path - to file, to directory
  • paths - ;-separated on Windows, :-separated on others

General, core

name type default description
OPENCV_SKIP_CPU_BASELINE_CHECK bool false do not check that current CPU supports all features used by the build (baseline)
OPENCV_CPU_DISABLE , or ;-separated disable code branches which use CPU features (dispatched code)
OPENCV_SETUP_TERMINATE_HANDLER bool true (Windows) use std::set_terminate to install own termination handler
OPENCV_LIBVA_RUNTIME file path libva for VA interoperability utils
OPENCV_ENABLE_MEMALIGN bool true (except static analysis, memory sanitizer, fuzzying, _WIN32?) enable aligned memory allocations
OPENCV_BUFFER_AREA_ALWAYS_SAFE bool false enable safe mode for multi-buffer allocations (each buffer separately)
OPENCV_KMEANS_PARALLEL_GRANULARITY num 1000 tune algorithm parallel work distribution parameter parallel_for_(..., ..., ..., granularity)
OPENCV_DUMP_ERRORS bool true (Debug or Android), false (others) print extra information on exception (log to Android)
OPENCV_DUMP_CONFIG bool false print build configuration to stderr (getBuildInformation)
OPENCV_PYTHON_DEBUG bool false enable extra warnings in Python bindings
OPENCV_TEMP_PATH path /tmp/ (Linux), /data/local/tmp/ (Android), GetTempPathA (Windows) directory for temporary files
OPENCV_DATA_PATH_HINT paths paths for findDataFile
OPENCV_DATA_PATH paths paths for findDataFile
OPENCV_SAMPLES_DATA_PATH_HINT paths paths for findDataFile
OPENCV_SAMPLES_DATA_PATH paths paths for findDataFile

Links:

Logging

name type default description
⭐ OPENCV_LOG_LEVEL string logging level (see accepted values below)
OPENCV_LOG_TIMESTAMP bool true logging with timestamps
OPENCV_LOG_TIMESTAMP_NS bool false add nsec to logging timestamps

Levels

  • 0, O, OFF, S, SILENT, DISABLE, DISABLED
  • F, FATAL
  • E, ERROR
  • W, WARNING, WARN, WARNINGS
  • I, INFO
  • D, DEBUG
  • V, VERBOSE

core/parallel_for

name type default description
⭐ OPENCV_FOR_THREADS_NUM num 0 set number of threads
OPENCV_THREAD_POOL_ACTIVE_WAIT_PAUSE_LIMIT num 16 tune pthreads parallel_for backend
OPENCV_THREAD_POOL_ACTIVE_WAIT_WORKER num 2000 tune pthreads parallel_for backend
OPENCV_THREAD_POOL_ACTIVE_WAIT_MAIN num 10000 tune pthreads parallel_for backend
OPENCV_THREAD_POOL_ACTIVE_WAIT_THREADS_LIMIT num 0 tune pthreads parallel_for backend
OPENCV_FOR_OPENMP_DYNAMIC_DISABLE bool false use single OpenMP thread

backends

Some modules have multiple available backends, following variables allow choosing specific backend or changing default priorities in which backends will be probed (e.g. when opening a video file).

name type default description
OPENCV_PARALLEL_BACKEND string choose specific paralel_for backend (one of TBB, ONETBB, OPENMP)
OPENCV_PARALLEL_PRIORITY_${NAME} num set backend priority, default is 1000
OPENCV_PARALLEL_PRIORITY_LIST string, ,-separated list of backends in priority order
OPENCV_UI_BACKEND string choose highgui backend for window rendering (one of GTK, GTK3, GTK2, QT, WIN32)
OPENCV_UI_PRIORITY_${NAME} num set highgui backend priority, default is 1000
OPENCV_UI_PRIORITY_LIST string, ,-separated list of highgui backends in priority order
OPENCV_VIDEOIO_PRIORITY_${NAME} num set videoio backend priority, default is 1000
OPENCV_VIDEOIO_PRIORITY_LIST string, ,-separated list of videoio backends in priority order

plugins

Some external dependencies can be detached into a dynamic library, which will be loaded at runtime (plugin). Following variables allow changing default search locations and naming pattern for these plugins.

name type default description
OPENCV_CORE_PLUGIN_PATH paths directories to search for core plugins
OPENCV_CORE_PARALLEL_PLUGIN_${NAME} string, glob parallel_for plugin library name (glob), e.g. default for TBB is "opencv_core_parallel_tbb*.so"
OPENCV_DNN_PLUGIN_PATH paths directories to search for dnn plugins
OPENCV_DNN_PLUGIN_${NAME} string, glob parallel_for plugin library name (glob), e.g. default for TBB is "opencv_core_parallel_tbb*.so"
OPENCV_CORE_PLUGIN_PATH paths directories to search for highgui plugins (YES it is CORE)
OPENCV_UI_PLUGIN_${NAME} string, glob highgui plugin library name (glob)
OPENCV_VIDEOIO_PLUGIN_PATH paths directories to search for videoio plugins
OPENCV_VIDEOIO_PLUGIN_${NAME} string, glob videoio plugin library name (glob)

OpenCL

Note: OpenCL device specification format is <Platform>:<CPU|GPU|ACCELERATOR|nothing=GPU/CPU>:<deviceName>, e.g. AMD:GPU:

name type default description
OPENCV_OPENCL_RUNTIME filepath or disabled path to OpenCL runtime library (e.g. OpenCL.dll, libOpenCL.so)
⭐ OPENCV_OPENCL_DEVICE string or disabled choose specific OpenCL device. See specification format in the note above. See more details in the Links section.
OPENCV_OPENCL_RAISE_ERROR bool false raise exception if something fails during OpenCL kernel preparation and execution (Release builds only)
OPENCV_OPENCL_ABORT_ON_BUILD_ERROR bool false abort if OpenCL kernel compilation failed
OPENCV_OPENCL_CACHE_ENABLE bool true enable OpenCL kernel cache
OPENCV_OPENCL_CACHE_WRITE bool true allow writing to the cache, otherwise cache will be read-only
OPENCV_OPENCL_CACHE_LOCK_ENABLE bool true use .lock files to synchronize between multiple applications using the same OpenCL cache (may not work on network drives)
OPENCV_OPENCL_CACHE_CLEANUP bool true automatically remove old entries from cache (leftovers from older OpenCL runtimes)
OPENCV_OPENCL_VALIDATE_BINARY_PROGRAMS bool false validate loaded binary OpenCL kernels
OPENCV_OPENCL_DISABLE_BUFFER_RECT_OPERATIONS bool true (Apple), false (others) enable workaround for non-continuos data downloads
OPENCV_OPENCL_BUILD_EXTRA_OPTIONS string pass extra options to OpenCL kernel compilation
OPENCV_OPENCL_ENABLE_MEM_USE_HOST_PTR bool true workaround/optimization for buffer allocation
OPENCV_OPENCL_ALIGNMENT_MEM_USE_HOST_PTR num 4 parameter for OPENCV_OPENCL_ENABLE_MEM_USE_HOST_PTR
OPENCV_OPENCL_DEVICE_MAX_WORK_GROUP_SIZE num 0 allow to decrease maxWorkGroupSize
OPENCV_OPENCL_PROGRAM_CACHE num 0 limit number of programs in OpenCL kernel cache
OPENCV_OPENCL_RAISE_ERROR_REUSE_ASYNC_KERNEL bool false raise exception if async kernel failed
OPENCV_OPENCL_BUFFERPOOL_LIMIT num 1 << 27 (Intel device), 0 (others) limit memory used by buffer bool
OPENCV_OPENCL_HOST_PTR_BUFFERPOOL_LIMIT num same as OPENCV_OPENCL_BUFFERPOOL_LIMIT, but for HOST_PTR buffers
OPENCV_OPENCL_BUFFER_FORCE_MAPPING bool false force clEnqueueMapBuffer
OPENCV_OPENCL_BUFFER_FORCE_COPYING bool false force clEnqueueReadBuffer/clEnqueueWriteBuffer
OPENCV_OPENCL_FORCE bool false force running OpenCL kernel even if usual conditions are not met (e.g. dst.isUMat)
OPENCV_OPENCL_PERF_CHECK_BYPASS bool false force running OpenCL kernel even if usual performance-related conditions are not met (e.g. image is very small)

SVM (Shared Virtual Memory) - disabled by default

name type default description
OPENCV_OPENCL_SVM_DISABLE bool false disable SVM
OPENCV_OPENCL_SVM_FORCE_UMAT_USAGE bool false
OPENCV_OPENCL_SVM_DISABLE_UMAT_USAGE bool false
OPENCV_OPENCL_SVM_CAPABILITIES_MASK num
OPENCV_OPENCL_SVM_BUFFERPOOL_LIMIT num same as OPENCV_OPENCL_BUFFERPOOL_LIMIT, but for SVM buffers

Links:

Tracing/Profiling

name type default description
⭐ OPENCV_TRACE bool false enable trace
OPENCV_TRACE_LOCATION string OpenCVTrace trace file name ("${name}-$03d.txt")
OPENCV_TRACE_DEPTH_OPENCV num 1
OPENCV_TRACE_MAX_CHILDREN_OPENCV num 1000
OPENCV_TRACE_MAX_CHILDREN num 1000
OPENCV_TRACE_SYNC_OPENCL bool false wait for OpenCL kernels to finish
OPENCV_TRACE_ITT_ENABLE bool true
OPENCV_TRACE_ITT_PARENT bool false set parentID for ITT task
OPENCV_TRACE_ITT_SET_THREAD_NAME bool false set name for OpenCV's threads "OpenCVThread-%03d"

Links:

Cache

Note: Default tmp location is TMPDIR% (Windows); $XDG_CACHE_HOME, $HOME/.cache, /var/tmp, /tmp (others)

name type default description
OPENCV_CACHE_SHOW_CLEANUP_MESSAGE bool true show cache cleanup message
OPENCV_DOWNLOAD_CACHE_DIR path default tmp location cache directory for downloaded files (subdirectory downloads)
OPENCV_DNN_IE_GPU_CACHE_DIR path default tmp location cache directory for OpenVINO OpenCL kernels (subdirectory dnn_ie_cache_${device})
OPENCV_OPENCL_CACHE_DIR path default tmp location cache directory for OpenCL kernels cache (subdirectory opencl_cache)

dnn

Note: In the table below dump_base_name equals to ocv_dnn_net_%05d_%02d where first argument is internal network ID and the second - dump level.

name type default description
OPENCV_DNN_BACKEND_DEFAULT num 3 (OpenCV) set default DNN backend, see dnn.hpp for backends enumeration
OPENCV_DNN_NETWORK_DUMP num 0 level of information dumps, 0 - no dumps (default file name ${dump_base_name}.dot)
OPENCV_DNN_DISABLE_MEMORY_OPTIMIZATIONS bool false
OPENCV_DNN_CHECK_NAN_INF bool false check for NaNs in layer outputs
OPENCV_DNN_CHECK_NAN_INF_DUMP bool false print layer data when NaN check has failed
OPENCV_DNN_CHECK_NAN_INF_RAISE_ERROR bool false also raise exception when NaN check has failed
OPENCV_DNN_ONNX_USE_LEGACY_NAMES bool false use ONNX node names as-is instead of "onnx_node!${node_name}"
OPENCV_DNN_CUSTOM_ONNX_TYPE_INCLUDE_DOMAIN_NAME bool true prepend layer domain to layer types ("domain.type")
OPENCV_VULKAN_RUNTIME file path set location of Vulkan runtime library for DNN Vulkan backend
OPENCV_DNN_IE_SERIALIZE bool false dump intermediate OpenVINO graph (default file names ${dump_base_name}_ngraph.xml, ${dump_base_name}_ngraph.bin)
OPENCV_DNN_IE_EXTRA_PLUGIN_PATH path path to extra OpenVINO plugins
OPENCV_DNN_IE_VPU_TYPE string Force using specific OpenVINO VPU device type ("Myriad2" or "MyriadX")
OPENCV_TEST_DNN_IE_VPU_TYPE string same as OPENCV_DNN_IE_VPU_TYPE, but for tests
OPENCV_DNN_INFERENCE_ENGINE_HOLD_PLUGINS bool true always hold one existing OpenVINO instance to avoid crashes on unloading
OPENCV_DNN_INFERENCE_ENGINE_CORE_LIFETIME_WORKAROUND bool true (Windows), false (other) another OpenVINO lifetime workaround
OPENCV_DNN_OPENCL_ALLOW_ALL_DEVICES bool false allow running on CPU devices, allow FP16 on non-Intel device
OPENCV_OCL4DNN_CONVOLUTION_IGNORE_INPUT_DIMS_4_CHECK bool false workaround for OpenCL backend, see https://github.com/opencv/opencv/issues/20833
OPENCV_OCL4DNN_WORKAROUND_IDLF bool true another workaround for OpenCL backend
OPENCV_OCL4DNN_CONFIG_PATH path path to kernel configuration cache for auto-tuning (must be existing directory), set this variable to enable auto-tuning
OPENCV_OCL4DNN_DISABLE_AUTO_TUNING bool false disable auto-tuning
OPENCV_OCL4DNN_FORCE_AUTO_TUNING bool false force auto-tuning
OPENCV_OCL4DNN_TEST_ALL_KERNELS num 0 test convolution kernels, number of iterations (auto-tuning)
OPENCV_OCL4DNN_DUMP_FAILED_RESULT bool false dump extra information on errors (auto-tuning)
OPENCV_OCL4DNN_TUNING_RAISE_CHECK_ERROR bool false raise exception on errors (auto-tuning)

Tests

name type default description
⭐ OPENCV_TEST_DATA_PATH dir path set test data search location (e.g. /home/user/opencv_extra/testdata)
⭐ OPENCV_DNN_TEST_DATA_PATH dir path $OPENCV_TEST_DATA_PATH/dnn set DNN model search location for tests (used by dnn, gapi, objdetect, video modules)
OPENCV_OPEN_MODEL_ZOO_DATA_PATH dir path $OPENCV_DNN_TEST_DATA_PATH/omz_intel_models set OpenVINO models search location for tests (used by dnn, gapi modules)
INTEL_CVSDK_DIR some dnn tests can search OpenVINO models here too
OPENCV_TEST_DEBUG num 0 debug level for tests, same as --test_debug (0 - no debug (default), 1 - basic test debug information, >1 - extra debug information)
OPENCV_TEST_REQUIRE_DATA bool false same as --test_require_data option (fail on missing non-required test data instead of skip)
OPENCV_TEST_CHECK_OPTIONAL_DATA bool false assert when optional data is not found
OPENCV_IPP_CHECK bool false default value for --test_ipp_check and --perf_ipp_check
OPENCV_PERF_VALIDATION_DIR dir path location of files read/written by --perf_read_validation_results/--perf_write_validation_results
⭐ OPENCV_PYTEST_FILTER string (glob) test filter for Python tests

Links:

videoio

Note: extra FFmpeg options should be pased in form key;value|key;value|key;value, for example hwaccel;cuvid|video_codec;h264_cuvid|vsync;0 or vcodec;x264|vprofile;high|vlevel;4.0

name type default description
⭐ OPENCV_FFMPEG_CAPTURE_OPTIONS string (see note) extra options for VideoCapture FFmpeg backend
⭐ OPENCV_FFMPEG_WRITER_OPTIONS string (see note) extra options for VideoWriter FFmpeg backend
OPENCV_FFMPEG_THREADS num set FFmpeg thread count
OPENCV_FFMPEG_DEBUG bool false enable logging messages from FFmpeg
OPENCV_FFMPEG_LOGLEVEL num set FFmpeg logging level
OPENCV_FFMPEG_DLL_DIR dir path directory with FFmpeg plugin (legacy)
OPENCV_FFMPEG_IS_THREAD_SAFE bool false enabling this option will turn off thread safety locks in the FFmpeg backend (use only if you are sure FFmpeg is built with threading support, tested on Linux)
OPENCV_FFMPEG_READ_ATTEMPTS num 4096 number of failed av_read_frame attempts before failing read procedure
OPENCV_FFMPEG_DECODE_ATTEMPTS num 64 number of failed avcodec_receive_frame attempts before failing decoding procedure
OPENCV_VIDEOIO_GSTREAMER_CALL_DEINIT bool false close GStreamer instance on end
OPENCV_VIDEOIO_GSTREAMER_START_MAINLOOP bool false start GStreamer loop in separate thread
OPENCV_VIDEOIO_MFX_IMPL num set specific MFX implementation (see MFX docs for enumeration)
OPENCV_VIDEOIO_MFX_EXTRA_SURFACE_NUM num 1 add extra surfaces to the surface pool
OPENCV_VIDEOIO_MFX_POOL_TIMEOUT num 1 timeout for waiting for free surface from the pool (in seconds)
OPENCV_VIDEOIO_MFX_BITRATE_DIVISOR num 300 this option allows to tune encoding bitrate (video quality/size)
OPENCV_VIDEOIO_MFX_WRITER_TIMEOUT num 1 timeout for encoding operation (in seconds)
OPENCV_VIDEOIO_MSMF_ENABLE_HW_TRANSFORMS bool true allow HW-accelerated transformations (DXVA) in MediaFoundation processing graph (may slow down camera probing process)
OPENCV_DSHOW_DEBUG bool false enable verbose logging in the DShow backend
OPENCV_DSHOW_SAVEGRAPH_FILENAME file path enable processing graph tump in the DShow backend
OPENCV_VIDEOIO_V4L_RANGE_NORMALIZED bool false use (0, 1) range for properties (V4L)
OPENCV_VIDEOIO_V4L_SELECT_TIMEOUT num 10 timeout for select call (in seconds) (V4L)
OPENCV_VIDEOCAPTURE_DEBUG bool false enable debug messages for VideoCapture
OPENCV_VIDEOWRITER_DEBUG bool false enable debug messages for VideoWriter
⭐ OPENCV_VIDEOIO_DEBUG bool false debug messages for both VideoCapture and VideoWriter

videoio tests

name type default description
OPENCV_TEST_VIDEOIO_BACKEND_REQUIRE_FFMPEG bool false test app will exit if no FFmpeg backend is available
OPENCV_TEST_V4L2_VIVID_DEVICE file path path to VIVID virtual camera device for V4L2 test (e.g. /dev/video5)
OPENCV_TEST_PERF_CAMERA_LIST paths cameras to use in performance test (waitAny_V4L test)
OPENCV_TEST_CAMERA_d_FPS num fps to set for N-th camera (0-based index) (waitAny_V4L test)

highgui

name type default description
$XDG_RUNTIME_DIR Wayland backend specific - create shared memory-mapped file for interprocess communication (named opencv-shared-??????)
OPENCV_HIGHGUI_FB_MODE string FB Selects output mode for the framebuffer backend (FB - regular frambuffer, EMU - emulation, perform internal checks but does nothing, XVFB - compatible with xvfb virtual frambuffer)
OPENCV_HIGHGUI_FB_DEVICE file path Path to frambuffer device to use (will be checked first)
FRAMEBUFFER file path /dev/fb0 Same as OPENCV_HIGHGUI_FB_DEVICE, commonly used variable for the same purpose (will be checked second)

imgproc

name type default description
OPENCV_OPENCL_IMGPROC_MORPH_SPECIAL_KERNEL bool true (Apple), false (others) use special OpenCL kernel for small morph kernel (Intel devices)
OPENCV_GAUSSIANBLUR_CHECK_BITEXACT_KERNELS bool false validate Gaussian kernels before running (src is CV_16U, bit-exact version)

imgcodecs

name type default description
OPENCV_IMGCODECS_AVIF_MAX_FILE_SIZE num 64MB limit input AVIF size
OPENCV_IMGCODECS_WEBP_MAX_FILE_SIZE num 64MB limit input WEBM size
OPENCV_IO_MAX_IMAGE_PARAMS num 50 limit maximum allowed number of parameters in imwrite and imencode
OPENCV_IO_MAX_IMAGE_WIDTH num 1 << 20, limit input image size to avoid large memory allocations
OPENCV_IO_MAX_IMAGE_HEIGHT num 1 << 20
OPENCV_IO_MAX_IMAGE_PIXELS num 1 << 30
OPENCV_IO_ENABLE_OPENEXR bool true (set build option OPENCV_IO_FORCE_OPENEXR or use external OpenEXR), false (otherwise) enable OpenEXR backend
OPENCV_IO_ENABLE_JASPER bool true (set build option OPENCV_IO_FORCE_JASPER), false (otherwise) enable Jasper backend
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