# Find Mid Point

Hi, i have some problems. I have a binary image and i want to find middle value by substracts x1 and x2 cols value. likewise, i want to subtracts y1 and y2. here is the code that i used : link text Thank's

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Find Mid Point

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1

What you want is the maxima and minima of the shape. Use something like this, with one scan of the image.

```
int x_min = img.cols, x_max = 0, y_min = img.rows, y_max = 0;
int r, c;
for( r = 0 ; r < img.rows ; ++r )
{
for( c = 0 ; c < img.cols ; ++c )
{
if( img.at< uchar >( r, c ) == 255 )
{
if( r < y_min )
y_min = r;
if( r > y_max )
y_max = r;
if( c < x_min )
x_min = c;
if( c > x_max )
x_max = c;
}
}
}
cv::Point middle( (int)(x_min+(x_max - x_min)/2), (int)(y_min+(y_max-y_min)/2) );
```

If you are more interested by the center of gravity of silhouette, try this sample, which draw the center with a circle, using the moment and findcontours (that you probably already used to detect your silhouette?)

1

0

I guess an even more easier option is to use the findContours function which will return a list of bounding boxes corresponding to the blobs in your image.

You can retrieve the measurements of this boundingbox, combined with the top left corner, which will give you all data that you actually need to calculate the center fast.

Asked: **
2013-07-15 22:11:23 -0600
**

Seen: **4,082 times**

Last updated: **Jul 16 '13**

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