eyal's profile - activity

I see. Thank u -:)

Hi All,

I have this very simple question that I can get figure it out.

Say I have function

void f(Mat m) { m.at<uchar>(3,3) = 17;}

when I call this function I see that the original Mat object is changed!! as far as I know object passing by value to function in c++ get copied so why when I pass Mat object the original matrix in being changed and not the copied one? Thank u in advance

Thank u for answering me :)

Hi All,

when I load an image via imread command I get the image size ,that is row and columns are inverted. For example say I have an jpg image of size 48x24 pixels (when I right clicked the mouse in windows explorer I see its properties) and whan I ask OpenCV to cout image.rows I get 24 and when I print out image.cols I get 48.

I can't figure it out why rows and cols are inverted in OpenCV

Thank u in advance

I don't see how the actual square size(real world size) is taken into account in the calibration process when using (i,j,0) for cornder at row i and column j.

Hi All,

I've read in the book "Learning OpenCV" by O'REILLY press and from "OpenCV 2 Computer Vision Application Programming Cookbook" by Robert Laganière (PACKT publishing) that when calibrating camera from chessboard pattern they use for 3D world coordinates the cornder indices with z = 0.

for example suppose chesboard cornders in vertical dimension is 4 and horizontal dimension 5 so the corresponding 3D world coordinates for calibration become:

(0,0,0), (0,1,0), (0,2,0),(0,3,0), (0,4,0), (1,0,0),(1,1,0),(1,2,0)...and so on. I understand we we can pick Z= 0 but I dont understand the one unit for each cornder coordinates I mean what if each sqaure in my image is say for example 44 cm? How does it reflects in the above calibration process?

Thank u in advance

Hi all,

I kind of new to OpenCV and I want to calculate canny edge detection to 8 bit (cv_8u) image. I know that canny uses sobel gradient operation. sobel gradient calculation performed on 8 bit image results in pixel values greater than 255 so my question is what range do I have to specify the lower and hi thresholds? in the range of 0-255 as in my original image or somthing else?

Thank u in advance

i see....thank u for ur answer!

Hi All,

Does openCV support 16 bit image calculations? say for example I have 16 bit image and I want to compute gradient of the image now the result may be greater than 16 bit image...any ideas?

Thank u in advance

I see...Thank u , you the best :)

First of all thank u very much for your answer!!

now I see why scale and delta are needed. But how do I know the output ranges if the derivatives I mean how do u know that derivatives of CV_8U map to [-1024,1024] ??

Hi All,

Im new to OpenCV and I'm trying for the past hour to understand what is the scale and delta input argument to cv::Sober function.

Can anyone help me?

Thank u in advance

Thank you!

Thank you!

Hi all,

I'm kind of new to OpenCv and I'm a little confused. Say I load and image via imread("someImage") into a Mat object named image. What is the difference between image.depth() and image.type() ??

I see it a lot in the documentations and tutorials and just don't get the difference.

I use OpenCV 2.4.2

Thank u in advance

Eyal