blobFromImage() 函数详解

blobFromImage()
Mat cv::dnn::blobFromImage ( InputArray image,
double scalefactor = 1.0,
const Size & size = Size(),
const Scalar & mean = Scalar(),
bool swapRB = false,
bool crop = false,
int ddepth = CV_32F
)
Python:
retval = cv.dnn.blobFromImage( image[, scalefactor[, size[, mean[, swapRB[, crop[, ddepth]]]]]] )

Creates 4-dimensional blob from image. Optionally resizes and crops image from center, subtract mean values, scales values by scalefactor, swap Blue and Red channels.

Parameters
image input image (with 1-, 3- or 4-channels).
size spatial size for output image
mean scalar with mean values which are subtracted from channels. Values are intended to be in (mean-R, mean-G, mean-B) order if image has BGR ordering and swapRB is true.
scalefactor multiplier for image values.
swapRB flag which indicates that swap first and last channels in 3-channel image is necessary.
crop flag which indicates whether image will be cropped after resize or not
ddepth Depth of output blob. Choose CV_32F or CV_8U.

if crop is true, input image is resized so one side after resize is equal to corresponding dimension in size and another one is equal or larger. Then, crop from the center is performed. If crop is false, direct resize without cropping and preserving aspect ratio is performed.

Returns
4-dimensional Mat with NCHW dimensions order.