Interactive Image Registration for Repeat Photography

Introduction

This is a tool, still in development, to register, i.e. align two images. It is aimed to register historic images and repeat photographs of the same scene.

Overview

On the left the old and new images are displayed on top of each other. Their visibility can be changed with the alpha slider in the right column or with the mouse wheel. At the top of the right column are magnifications of the image area around the mouse cursor is shown. The left magnification is of the second image. The right magnification is of the first image. Below are interfaces to upload images, change image visibility, colour one image red and the other green, a row of tool selection buttons, an undo and a reset button, and a button to create download links to the registered images.

Workflow

1. Use the existing images or upload new first and second images by clicking the browse buttons on the right.
2. Hover with the mouse over the two blended images on the left. Change the blending with the mousewheel or the alpha slider. You see a magnification of both images to the right.
3. Select a prominent feature point in the fist image by clicking with your left mouse button on this feature point in the blended images. In the beginning select a point in the first/old image. Alternatively you may draw a rectangle around the feature point by clicking and holding the left mouse button. Then the feature point is selected automatically. Check that the feature point exists in both images using the magnification on the right.
4. After selecting the feature point in one image, the other image becomes active. The active image, in which you can position a point has a crossbar in the magnification.
5. Select the same feature point in the now active image.
6. The second image is moved so that the feature point is aligned perfectly.
7. Repeat Step 3 and 4 to select a second feature point in both images.
8. Now the second image is scaled and rotated to register both feature points.
9. Repeat Step 3 and 4 two times to select a third and fourth feature point.
10. A perspective transformation is computed to align all four feature points.
11. You can now mark more points. An optimal transformation is then computed. However, it is geometrically impossible to align more than four points perfectly.
12. At all times you can switch the tools Mark Points, Move Points, Delete Points, Crop Images, or Time Reveal.
13. At all times you may use the alpha slider to make the first or second image more visible. You can also use the mouse wheel to adjust the alpha value. You may also use the Red Green Toning Slider to colour the images to check the quality of the registration.

Tools

Mark Points: Either click in the images or draw a rectangle by pressing and holding the left mouse button and moving the mouse.

Move Points: Move the point nearest to the mouse position when holding the left mouse button and moving the mouse. Note: The images are directly transformed again, thus, the second image moves but the point stays fixed.

Delete Points: Points inside a rectangle drawn by pressing and holding the left mouse button and moving the mouse are deleted.

Crop Images: Draw a rectangle(yellow) with the mouse. The rectangle is shown in the images. The downloaded images are cropped to the yellow rectangles size.

Time Reveal: In this mode you can reveal parts of the first image around the mouse position in the second image. Just try it.

Undo: Removes the last point.

Reset: Deletes all points and undoes all transformations.

Create Download Links: Click on Create Download Links to create two links to full resolution cropped and transformed images.

Keyboard Shortcuts

Keyboard Shortcuts for various functions are displayed inside square brackets in the corresponding buttons.

Tips

• Points should be as far from each other as possible.
• Ideally the first four points should be positioned on the same plane in the scene. E.g. a housefront.
• After marking the third point pair no transformation is computed. This is intended.

Cite

If you use this program for your work please cite our paper:

Axel Schaffland, Oliver Vornberger, and Gunther Heidemann. “An Interactive Web Application for the Creation, Organization, and Visualization of Repeat Photographs.” Proceedings of the 1st Workshop on Structuring and Understanding of Multimedia heritAge Contents. 2019.

https://doi.org/10.1145/3347317.3357247

Feedback

Please send feedback to axschaffland (at) uni-osnabrueck.de

Related

Our portal www.re.photos for the creation, collection, organisation, and discussion of repeat photographs.