Transformation of images with known proportions

You may have an image whose proportions are known but which has perspective skew, rotation and shift.  Photographing a painting, drawing or map with a hand-held camera can serve as an example.

0) Measure the width and height of the picture in centimetres, millimetres or any other consistent units.

1) Take the photograph, without worrying too much about the image being straight on.  

2) Use a long focal length zoom lens to reduce radial lens distortion if you have one.  If this is not possible, use a radial distortion correction programme like RadCor or PTLens to treat the image before opening it in AirPhotoSE. Download the image from the camera normally. 

3) Open it in AirSE with the File Opening button or equivalent menu item.   Use any of the enhancement or filtering image treatment options in AirPhotoSE if desired.


4) On the Control menu, select the Hide/Show Quadrilateral option.

5) Hold down Shift and the left mouse button and move the corners of the quadrilateral to match the corners of the picture frame.  It is usually helpful to display the image at full resolution using the navigation window (F4) and go to each corner in turn either by dragging in the navigation window or with a right mouse click to show an overview with control points.

Click on the Transform menu and then on the item Transform to Clone and Crop.

6)  In the dialogue box which pops up enter the width and height of the image as measured initially. Set the value of the border field to 0% if you don't want a border or to a value between 1 and 10% of the total image width or height whichever is smaller.

The image will be transformed.


Save the result under a suitable name when the image is closed.

If you are planning to print via a commercial service and you need to submit images with a standard side ratio format (e.g. 4 x 3, 3 x 2 etc.) to fit the paper sizes offered by the provider (e.g. 13 x 10, 30 x 20) without having parts of the image cropped in their automated printing machines, a border of at least 5% will help to prevent this from happening. The border can be white or black.  In Options-Appearance, choose White or Black background.