The benefit of cropping Illustrated


It has been stated in another page of the tutorial that placing in different order the list of images source in PTGui or PTMac may give different results after blending. If the images were simply cropped to the limit of the Circle produced by the Fisheye and if the Nadir and Zenith images were placed last in the list, muddy result would occur.

However it was shown that cropping the source image to a smaller square alleviate the problem: only the "sweet spot" of the image is taken into account. The resulting panorama is of the best sharpness that can be. Many parameters and different software options have a role in the problem. A synthesis was established to show as much as possible the problem. Click on the "SYNTHESIS" button at the top of this page for more details if you wish.

Illustration of Three typical cases

Three different Panoramas were made, each from six photographs with an Canon EOS 20D camera and 8 mm fisheye lens. Four shots around plus Nadir and Zenith.

Processed through PTGui 5 and blended with Smartblend. This is only one amongst many other cases that could of course have been shown.

These rectangular images below are QuickTime VR object movies. Use the arrow keys of the keyboard or drag the mouse sideways (left or right) on the image itself.

The first frame shows the rendered and blended Panorama. The other frame images are the individual layers that were fed to smartblend. Note the different colored grid that makes easy to spot where part of the Panorama image came from corresponding part of the source image.

You also should see a square Cubic QTVR below each flat panorama. Thus you may compare the three visual experiences.


The following QTVR Files are quite large.

Depending on your available bandwidth you may expect some time for loading.

First example: Not cropped and bad ranking in the list

The source Images had been cropped to the 180 degree circle. The Zenith and Nadir were placed last in the list of Source Images.

The Zenith image (red) was not correctly rendered as two images (blue and cyan) from the sides have covered half of the Zenith area up to the Zenith pole itself.

In a similar manner, the Nadir area is not covered by the Nadir shot (orange) as one would have expected. In fact most of the surface is covered by three tongues of the side images (cyan, green, magenta). The resulting quality is considerably reduced in these two regions (top and bottom) and some of the worst parts of the side images were not cropped out and are apparent.

One can even see that a leg from my tripod is now visible on the Nadir of the final panorama while there was none on the specific Nadir shot!

Second example: Not cropped but better ranking in the list

Once again, only basic cropping was performed (as above) to 180 deg circle. But the Zenith and the Nadir images were this time placed at the top of the list of Source Images.

The Zenith and the Nadir are here much less spoiled by the side images. The Nadir (orange) is correctly given its normal space. But the Zenith (red) is still spoiled a bit by the (magenta) and (blue) images from the side. This panorama would be thought as good because the defect is rather subtile and hard to pinpoint. Anyhow the panorama is of a reduced quality overall.

Third example: Cropped images is the best to be done (wathever the rank in the list)

Note that here the Nadir and the Zenith Image were placed here at the worst rank in the Source Image list (the end).

Smart-Cropping was performed. All the images were cropped to a square leaving only the best part of the fisheye image to be seen. The resulting panorama is composed of equal "square" surfaces and equal images. The total panorama is in fact composed of the regular six faces of a cube. Quality is best possible. The panorama image shall be crisp and sharp.