Re: post-process photos of flat rectangular objects to remove perspective

Hugo Trebl <singalong@xxxxxxxxxxx> wrote:
Hi,

I am looking for a tool to post-process the following type of photo:

Given a series of photos of flat rectangular objects, such as book
covers, letters, magazines, posters, taken against an uniform
background.

One object per photo, slightly skewed and rotated due to perspective,
since the camera is usually not exactly aligned. (suppose a scanner is
not an option)

I am searching for a tool that allows quick post-processing to remove
the distortion introduced by the perspective, and to discard
unnecesary background. In the end the object should be aligned with
the picture borders and fill the whole picture

So either this tool should be able to recognize the rectangular shape
automatically and guess the correct transformation, or let me quickly
change the shear/rotation/cut manually until the object fits.
Optionally there would also be a filter to remove glare.

Most image manipualtion software can already do the manual part
somewhat, but at least with the Gimp is very cumbersome to do this for
a series of pictures and requires lots of adjustments and clicks.

Is there any tool good for this sort of task?

If the camera has a live view LCD which can have a rectangular grid
projected onto it you can use the grid to align a hand held shot of a
rectangular object so that this kind of post processing is
unnecessary. If the camera doesn't have a grid option I'd be tempted
to print a transparent foil with a grid and stick it over the LCD for
such shots.

In some cases, such as rectangular things hanging on walls, you can't
always get the height to stop a vertical convergence, but using a grid
to get exactly on the centre line stops horizontal convergence and
makes the post processing to fix the vertical much easier.

--
Chris Malcolm cam@xxxxxxxxxxxxxxxxxxxx DoD #205
IPAB, Informatics, JCMB, King's Buildings, Edinburgh, EH9 3JZ, UK
[http://www.dai.ed.ac.uk/homes/cam/]

.

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