## Environment Variables

On startup and during different operations, mrViewer reads several environment variables that allow you to customize its operation. Here's a list of them:

Variable | Explanation | Default Value
--- | --- | ---
CTL_MODULE_PATH | A string of colon (Unix) or semicolon (Windows) separated paths that mrViewer will use to find .ctl scripts. | If unset, mrViewer's ctl directory
MRV_ODT_CTL_DISPLAY_TRANSFORM | The CTL script used to transform images from CIExy space for display on your screen | transform_display_video
MRV_ODT_ICC_PROFILE | The ICC profile attached to the monitor to simulate the output media. | None.
MRV_ODT_CTL_DISPLAY_CHROMATICITIES | Chromaticities of your display | Rec. ITU-R BT.709 chromaticities
MRV_ODT_CTL_DISPLAY_WHITE_LUMINANCE | White Luminance of your display | 120 candelas per square meter
MRV_ODT_CTL_DISPLAY_SURROUND_LUMINANCE | Luminance of the surrounding environment | 12 candelas per square meter
DO_NOT_USE_FFMPEG_PNG | Use ImageMagick's PNG reader instead of FFMPEG's one. The ImageMagick reader is slower but more compatible and allows all sorts of gaps in the sequence. | Not set
MRV_CTL_RT_8bit | A default CTL script used to transform 8-bit images from RGB to CIExy space | None.
MRV_CTL_RT_16bit | A default CTL script used to transform 16-bit images from RGB to CIExy space | None.
MRV_CTL_RT_32bit | A default CTL script used to transform 32-bit images from RGB to CIExy space | None.
MRV_CTL_RT_float | A default CTL script used to transform float and half float images from RGB to CIExy space | transform_RRT
MRV_ICC_RT_8bit | A default ICC profile used to transform 8-bit images from RGB to CIExy space | None.
MRV_ICC_RT_16bit | A default ICC profile used to transform 16-bit images from RGB to CIExy space | None.
MRV_ICC_RT_32bit | A default ICC profile used to transform 32-bit images from RGB to CIExy space | None.
MRV_ICC_RT_float | A default ICC profile used to transform float and half float images from RGB to CIExy space | None.
MRV_OCIO_8bits_ICS | A default OCIO transform for 8 bits images | None.
MRV_OCIO_16bits_ICS | A default OCIO transform for 16 bits images | None.
MRV_OCIO_float_ICS | A default OCIO transform for half and full float images | None.
MRV_ICC_RT_float | A default ICC profile used to transform float and half float images from RGB to CIExy space | None.
ICC_PROFILES | Directory where ICC and ICM profiles reside | %WINDIR%/SYSTEM32/spool/drivers/color on Windows and /usr/share/color/icc on Unix
HOME | Home directory for user where mrViewer's preferences will be stored | $HOME on Unix and %HOME% (or %HOMEDRIVE%%HOMEPATH% ) on Windows
MRV_SHADER_PATH | Directory where mrViewer's hardware shaders reside. | Undefined, mrViewer uses a built-in shader.