How to convert bounding box (x1, y1, x2, y2) to YOLO Style (X, Y, W, H)

Issue

I’m training a YOLO model, I have the bounding boxes in this format:-

x1, y1, x2, y2 => ex (100, 100, 200, 200)

I need to convert it to YOLO format to be something like:-

X, Y, W, H => 0.436262 0.474010 0.383663 0.178218

I already calculated the center point X, Y, the height H, and the weight W.
But still need a away to convert them to floating numbers as mentioned.

Solution

YOLO normalises the image space to run from 0 to 1 in both x and y directions. To convert between your (x, y) coordinates and yolo (u, v) coordinates you need to transform your data as u = x / XMAX and y = y / YMAX where XMAX, YMAX are the maximum coordinates for the image array you are using.

This all depends on the image arrays being oriented the same way.

Here is a C function to perform the conversion

#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <math.h>

struct yolo {
    float   u;
    float   v;
    };

struct yolo
convert (unsigned int x, unsigned int y, unsigned int XMAX, unsigned int YMAX)
{
    struct yolo point;

    if (XMAX && YMAX && (x <= XMAX) && (y <= YMAX))
    {
        point.u = (float)x / (float)XMAX;
        point.v = (float)y / (float)YMAX;
    }
    else
    {
        point.u = INFINITY;
        point.v = INFINITY;
        errno = ERANGE;
    }

    return point;
}/* convert */


int main()
{
    struct yolo P;

    P = convert (99, 201, 255, 324);

    printf ("Yolo coordinate = <%f, %f>\n", P.u, P.v);

    exit (EXIT_SUCCESS);
}/* main */

Answered By – Jon Guiton

Answer Checked By – Senaida (AngularFixing Volunteer)

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