How to convert an image from perspective projection to orthographic projection?

Question

Sometimes you want to make a 2D image on the computer from a real life 2D image, but for whatever reason you can't get a straight, front-on view of the image.

Say it's a billboard and you can only photograph it from street level.

Such photos will have a 3D perspective of the surface. Is there a tool, app, website, etc that can turn such a photo into a regular 2D rectangular image?

Best would be a tool which uses photogrammetry. But a tool that detects the four edges of the distorted rectangle, or lets the user indicate them, would also be of interest.

Answer 1

GIMP has a Perspective Tool.

You can use it to undo some perspective effects, just select your layer and use corner handles to get desired effect. GIMP will render fast low quality preview to give you some idea of how it will look, then you can confirm handle positions to render final image.

Answer 2

Some time after asking this question, but a few years ago now, I somehow found Microsoft Office Lens, though it's since changed its name to Microsoft Lens.

I've been using the Android version but there's also an iPhone version and a Windows version. (Nothing for my new M1 Mac yet though).

You can take a photo through the app, or with the camera app and then choose the photo from the gallery.

If you're taking the photo through the app, it smoothly draws in a live updating rectangle around what it considers the most likely target.

It then shows your photo with the four vertexes and four edges overlaid in red and you can adjust them on the touch screen. It tries to "snap to" other edges as you slide close to them, but doesn't always get this right. You can pinch-zoom to make fine adjustments.

There are actually many competing apps and I tried several at the time but found Microsoft's effort to be the most polished and the one that fit my use-cases best. Most such apps have the words "scan" or "scanner" in their name. It seems their main target market is scanning dockets and business cards to import into office software, but they work just as well on billboards.

Answer 3

PhotoShops "perspective" is able to do a "3D" rotation and aspect, and resizing operation of a selecting chunk of the picture. That is what I would attempt to use to do that. You could never get it as clean and perfect and really front facing because of all the other objects that would be captured (also) from that angle, only the main 2D surface.

Photoshop also had various pinch and pucker and twisting and parellel offseting tools and filters. I had used photoshops simple squeeze and twist and pinch kind of tools for lens distortion before specific lens distortion filters were even in the programs (more redundant features). Many high-end photo programs have the Barrel distortion and pin distortion adjustements, that adjusts for only the lens distortions , not the perspective offset.

I find stiching is best done manually even with the best stiching tools simple crop trim and layering. use clone tool cleanup, and a bit of manuel smudging softening or blending. If your going to stich, a tripod can be very useful, what you start with it more important than trying to "fix" it later.

Getting into all these angles and multiples and perspective, your really going to want a good original picture to work with. Higher resolution and way less Jpeg compressing than gets done in most phones and cheap cameras.

Adding panarama stiching to perspective rotations is going to be more trouble than getting permission to go on a property to get the pic right the first time. But then I am sure you know there is only one way to get it right, and that is to have done it right from start to finish. Anything else will still be fun and get it done, just never perfected.