Difference between revisions of "Stitching 2008 State of the Art"

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==Stitching Images - the State of the Art in 2008==
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== Introduction ==
  
What you can expect to achieve with stitching software current in 2008.
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Stitching is about making one large image from several smaller photos.
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The ambition is to have the fact of individual ingredient photos no longer show through in the resulting image.
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This page shows what stitching software actually does.
  
 
If you want to know how to achieve this, or what
 
If you want to know how to achieve this, or what
 
[[software]] to use, please read a [[Tutorials|tutorial]] instead.
 
[[software]] to use, please read a [[Tutorials|tutorial]] instead.
 
What can be done and what quality can be achieved,
 
What can be done and what quality can be achieved,
this shall be demonstrated step by step with the two images below.
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this shall be demonstrated step by step starting with the two photos below.
  
 
[[Image:Img08232.jpg|300px]] [[Image:Img08231.jpg|300px]]
 
[[Image:Img08232.jpg|300px]] [[Image:Img08231.jpg|300px]]
  
At the time of photography, some [[Photography Guidelines|guidelines]] have been followed that make the photos good raw material for proper stitching.
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At the time of photography, some [[Photography Guidelines|guidelines]] have been followed that make the photos good stitching material.
  
 
----
 
----
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For comparison to stitching proper, the two photos have simply been overlayed in a standard
 
For comparison to stitching proper, the two photos have simply been overlayed in a standard
 
image editing and retouching software.  
 
image editing and retouching software.  
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[[Image:Img0823xoverlay1.jpg|300px]] [[Image:Img0823xoverlay2.jpg|300px]]
 
[[Image:Img0823xoverlay1.jpg|300px]] [[Image:Img0823xoverlay2.jpg|300px]]
  
The attempt to use such software for stitching produces results of inferiour quality.
 
 
Please notice in particular the misalignment of geometrical features in the left image,
 
Please notice in particular the misalignment of geometrical features in the left image,
 
and the roof misorientation in the right one.
 
and the roof misorientation in the right one.
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----
 
----
  
Have a look at the following aspects to see where one can do better,
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Have a look at the following aspects to see where proper stitching software can do better.
with usually a choice of either fully automatic,
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Such software usually gives a choice of either performing these steps fully automatically,
or software assistance for optimisations without try-and-error workflow.
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or provide assistance for optimisations without requiring a try-and-error workflow.
  
 
===Remapping===
 
===Remapping===
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To project the images onto the same virtual screen, they need
 
To project the images onto the same virtual screen, they need
to be remapped, as shown above. Including a keystone correction as in this example
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to be remapped, as shown above. Correcting falling lines as in this example
 
is by choosing an appropriate orientation for the virtual screen.
 
is by choosing an appropriate orientation for the virtual screen.
  
 
[[Image:Img0823xstitch3.jpg|500px]]
 
[[Image:Img0823xstitch3.jpg|500px]]
  
Handheld photos are fine.
 
 
The relative camera orientation, and the lense parameters
 
The relative camera orientation, and the lense parameters
 
are determined from the images overlap area.
 
are determined from the images overlap area.
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Handheld photos are fine.
 
If the photos have been taken from the same point,
 
If the photos have been taken from the same point,
 
expect alignment accuracy of better than a pixel.
 
expect alignment accuracy of better than a pixel.
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State of the art is a seam mechanism that behaves
 
State of the art is a seam mechanism that behaves
like a line for small details but averages for large scale differences.
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like a line for small details but averages for large scale features.
  
 
[[Image:Img0823xstitch6.jpg|500px]]
 
[[Image:Img0823xstitch6.jpg|500px]]
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This is the overall result, cropped to rectangular shape,
 
This is the overall result, cropped to rectangular shape,
for a state-of-the-art stitching of images in the year 2008.
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for a state-of-the-art stitching of two photos.
  
[[Category:Info]]
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[[Category:How it works]]

Revision as of 11:42, 4 May 2008

Introduction

Stitching is about making one large image from several smaller photos. The ambition is to have the fact of individual ingredient photos no longer show through in the resulting image. This page shows what stitching software actually does.

If you want to know how to achieve this, or what software to use, please read a tutorial instead. What can be done and what quality can be achieved, this shall be demonstrated step by step starting with the two photos below.

Img08232.jpg Img08231.jpg

At the time of photography, some guidelines have been followed that make the photos good stitching material.


For comparison to stitching proper, the two photos have simply been overlayed in a standard image editing and retouching software.

Img0823xoverlay1.jpg Img0823xoverlay2.jpg

Please notice in particular the misalignment of geometrical features in the left image, and the roof misorientation in the right one.


Have a look at the following aspects to see where proper stitching software can do better. Such software usually gives a choice of either performing these steps fully automatically, or provide assistance for optimisations without requiring a try-and-error workflow.

Remapping

Img08232remap.jpg Img08231remap.jpg

To project the images onto the same virtual screen, they need to be remapped, as shown above. Correcting falling lines as in this example is by choosing an appropriate orientation for the virtual screen.

Img0823xstitch3.jpg

The relative camera orientation, and the lense parameters are determined from the images overlap area. Handheld photos are fine. If the photos have been taken from the same point, expect alignment accuracy of better than a pixel.

Exposure

Img0823xstitch4.jpg

Input images need not have the same exposure, or white balance. Together with vignetting (images are darker in the corners than in the middle) the required corrections can be derived from images with a suitably large overlap area.

Blending

Obviously, there needs to be some kind of seam between the images, but one can do better than a hard seam line (used above) or a feathered transition that affects the image character.

Img0823xstitch5.jpg

State of the art is a seam mechanism that behaves like a line for small details but averages for large scale features.

Img0823xstitch6.jpg

In addition, the seam line should be placed intelligently to avoid cutting through objects (like cloud, car or bicycle) that have moved in the time between taking the images.

Overall Result

Img0823xstitch6crop.jpg

This is the overall result, cropped to rectangular shape, for a state-of-the-art stitching of two photos.