что означает флаг -1 в imread из opencv

Question

Я вижу код: Mat imgOrg = imread( fileName, -1 );. К какому типу флага imreadmodes относится аргумент -1?

Answer 1

Флаги и соответствующие значения: из OpenCV imgcodecs.hpp

   IMREAD_UNCHANGED            = -1, //!< If set, return the loaded image as is (with alpha channel, otherwise it gets cropped).
   IMREAD_GRAYSCALE            = 0,  //!< If set, always convert image to the single channel grayscale image (codec internal conversion).
   IMREAD_COLOR                = 1,  //!< If set, always convert image to the 3 channel BGR color image.
   IMREAD_ANYDEPTH             = 2,  //!< If set, return 16-bit/32-bit image when the input has the corresponding depth, otherwise convert it to 8-bit.
   IMREAD_ANYCOLOR             = 4,  //!< If set, the image is read in any possible color format.
   IMREAD_LOAD_GDAL            = 8,  //!< If set, use the gdal driver for loading the image.
   IMREAD_REDUCED_GRAYSCALE_2  = 16, //!< If set, always convert image to the single channel grayscale image and the image size reduced 1/2.
   IMREAD_REDUCED_COLOR_2      = 17, //!< If set, always convert image to the 3 channel BGR color image and the image size reduced 1/2.
   IMREAD_REDUCED_GRAYSCALE_4  = 32, //!< If set, always convert image to the single channel grayscale image and the image size reduced 1/4.
   IMREAD_REDUCED_COLOR_4      = 33, //!< If set, always convert image to the 3 channel BGR color image and the image size reduced 1/4.
   IMREAD_REDUCED_GRAYSCALE_8  = 64, //!< If set, always convert image to the single channel grayscale image and the image size reduced 1/8.
   IMREAD_REDUCED_COLOR_8      = 65, //!< If set, always convert image to the 3 channel BGR color image and the image size reduced 1/8.
   IMREAD_IGNORE_ORIENTATION   = 128 //!< If set, do not rotate the image according to EXIF's orientation flag.

То есть -1 означает UNCHANGED

Answer 2

Флаги режима определены в imgcodecs.hpp https://github.com/opencv/opencv/blob/master/modules/imgcodecs/include/opencv2/imgcodecs.hpp