openCV

DAY ONE

Load, change and save pictures.

LOAD IMAGE -> cv::imread
CHANGE IMAGE -> cv::cvtColor
SAVE IMAGE -> cv::imwrite

cv::imread

Function:

Load a picture file as a ‘Mat’ object.

Arguments:

FIRST: image file name

SECOND: type of current image file

Types:

IMREAD_UNCHANGED(<0) -> load the origin image, no any changes.

IMREAD_GRAYSCALE(0) -> load the gray scale image.

IMREAD_COLOR(>0) -> load the RGB image. (DEFAULT)

For example:

void easyimg(){
    string oriPath = "/home/baizeyv/Pictures/t.jpg";
    Mat oriImg = imread(oriPath);
    imshow("origin image", oriImg);
    waitKey(0);
}

cv::namedWindow

Function:

Create an opencv window which is created and released automatically, we don’t need to destroy it.

Usage:

namedWindow(“Window Title”, WINDOW_AUTOSIZE);

WINDOW_AUTOSIZE will auto resize the window according to the size of image, but cannot be resized by manually.

WINDOW_NORMAL when use it and integrated with QT, it can be adjusted the window size.

cv::imshow

Function:

Display the image to the window according to the window title.

Arguments:

FIRST: window title

SECOND: Mat Object

cv::cvtColor

Function:

It can switch the color space to the another, it has three argument.

Arguments:

FIRST: origin image

SECOND: changed image

THREE: origin and color space of target, for example, COLOR_BGR2HLS , COLOR_BGR2GRAY etc.

Usage:

cvtColor(image, gray_image, COLOR_BGR2GRAY);

cv::imwrite

Function:

Save current image file to the fixed path.

Only the BGR image of png, jpg, tiff file of 8 bit or 16 bit which is single channel or three channels can be saved by this way.

When saving the png file, it can save the transparency channel images.

We can specify the compress arguments.

Arguments:

FIRST: output file path and name

SECOND: the Mat Object which will be saved

DAY TWO

Get the pointer of image pixel.

CV_Assert

CV_Assert(myImage.depth() == CV_8U);

Mat.ptr<uchar>(int i=0) -> Get the pointer of pixel matrix, the index i express the number of lines, count from zero.

const uchar* current=myImage.ptr<uchar>(row); -> Get the current line pointer.

p(row, col)=current[col] -> Get the value of pixel of current pixel point P(row, col).