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c#rectanglesbounding-boxrescale
Hani Goc
Hani Goc

Reputation: 2441

Rescale rectangle (Top, Left, Bottom, right)

Original question: Original question

I have an image I1 of size height x width = (1500,500) resized to (500,300).

I1 contains bounding boxes characterized by their coordinates (Top, Left, Bottom, Right).

How can rescale the coordinates of the bounding boxes when The size of I1 is changed? are these formulas correct?

   double newTop = Math.Ceiling((top) * (double)pictureBox1.Height / (double)image1.Height);
   double newLeft = Math.Ceiling((left) * (double)pictureBox1.Width / (double)image1.Width);
   double newBottom = Math.Ceiling((bottom + 1) * (double)pictureBox1.Height / (double)image1.Height) - 1;
   double newRight = Math.Ceiling((right + 1) * (double)pictureBox1.Width / (double)image1.Width) - 1;

Upvotes: 0

Views: 2605

Answers (1)

Ben Voigt
Ben Voigt

Reputation: 283624

In general:

Sizes scale by the factor (new-size)/(old-size).

Coordinates are a bit more complex:

x2 = left2 + (x1 - left1) * width2 / width1
y2 = top2 + (y1 - top1) * height2 / height1

where left and width, etc describe the location of the entire image. x and y describe the feature being transformed. In your case, corners of the bounding boxes are features.

If left1, left2, top1, top2 are all zero, you will get expressions similar to yours.

Upvotes: 1

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