Photo perspective correction

General Discussion Other

nemecsek

in General Discussion • Other • 7 months ago

Hi. I searched everywhere but cannot find an EASY way to make perspective correction on a photo.

I would like to:

1) visualize the original snapshot of a building (distorted because taken from ground level)

2) pinpoint the 4 corner points of the facade (assuming it is rectangular in reality)

3) transform the facade quadrilateral to a rectangle. I only need the facade, I can crop whatever is outside the quadrilateral.

As the snapshot is taken from afar only little correction is necessary. Final image quality is not a big issue. Lenses distortion are not so visible and a little "curved" border wall is also acceptable (no need to work on this).

Could you tell me what to use (possibly a library)?

I tried JHLabs' PerspectiveFilter but it works reversed to what I need: it takes the original snapshot and converts it to the quadrilateral defined by the 4 points...

Thank you for any help

Alex

Replies(2)

tfguy44

Re: Photo perspective correction

7 months ago

Something like this?
Mouse key to move green corner dot.

Space bar to cycle to next dot.

HIGHLY UNTESTED AND NO CONSTRAINS IN CODE ADDED.
EXAMPLE CODE ONLY, USE AT YOUR OWN RISK.

import processing.opengl.*;
int a=100, b=100, c=200, d=100, e=200, f=200, g=100, h=200;
int n=0;
PImage img;
void setup() {
size(800, 400, OPENGL);
img = loadImage( "http://www.ap-logic.com/images/img_imcBuilding.jpg" );
}
void draw() {
background(0);
image( img, 0, 0 );
noStroke();
beginShape(QUAD);
texture( img.get() );
vertex(400, 0, a, b);
vertex(800, 0, c, d);
vertex(800, 400, e, f);
vertex(400, 400, g, h);
vertex(400, 0, a, b);
endShape();
fill(255, 0, 0);
if( n==0 ){ fill(0,255,0); } ellipse(a, b, 5, 5); fill(255, 0, 0);
if( n==1 ){ fill(0,255,0); } ellipse(c, d, 5, 5); fill(255, 0, 0);
if( n==2 ){ fill(0,255,0); } ellipse(e, f, 5, 5); fill(255, 0, 0);
if( n==3 ){ fill(0,255,0); } ellipse(g, h, 5, 5); fill(255, 0, 0);
}
void mousePressed(){
if( n == 0 ){
a = mouseX; b = mouseY;
}
if( n == 1 ){
c = mouseX; d = mouseY;
}
if( n == 2 ){
e = mouseX; f = mouseY;
}
if( n == 3 ){
g = mouseX; h = mouseY;
}
}
void keyPressed(){
if( key == ' ' ){
n++;
n%=4;
}
}

nemecsek

Re: Photo perspective correction

7 months ago

tfguy44, this is perfectly what I meant!

It is just strange that there are some artefacts: it looks like the quadrilateral to transform is managed as 2 triangles and minimal errors in corner positioning are very visible as broken lines. But this is not an issue for me.

Thank you very much for the effort to write me some working code.

Have a nice day

Alex

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