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4 Viewing Images and Cubes with the Multibeam


Note that this tool will be replaced with the more powerful <kvis> programme.

The <MultibeamView> programme allows you to view two datasets. This allows you to compare different datasets in a very easy fashion. This programme uses the ImageDisplay widget (section 2.15) to provide the usual interface. Pressing the View button will pop up the View2Datasets widget.      This widget provides an advanced control for two datasets (either two-dimensional or three-dimensional). It allows the user to display one dataset or the other, overlay contours of one over the other, show profiles along any axis, and much more. The controls provided are:

  In addition, if you click the left mouse button in the display window without moving it in between the press and release, the image will pan across. If you click the middle mouse button, the image will zoom in 2x (the new centre of the image will be the place where you clicked). Click the right mouse button to zoom out 2x. If the profile mode is ``box'' then you can't use the middle mouse button to zoom.

     Pressing the c key in the display window will compute and display a scatter plot of intensity values in one image versus intensity values in the other image. This is useful for seeing if there is a correlation between the values in the two images. You can use the left mouse button to define a sub-image (similarly to zooming in) from which the scatter plot is computed.

A screen snapshot is available here.

Command-line Options


The following command-line options are supported by <MultibeamView>:

4.2 Special Movies

If you want to play a movie that was made using the Hot Gas Substances or the Hot Gas Continuous shaders of the xray volume rendering tool, you should compress this movie from 24-bit to 8-bit. Movies made with the other algorithms do not require compression and can be played directly. The compression of 24-bit movies is done with the command:

conv_24to8 -com w -max <max num of colours> - <inmovie>

The switch -com w tells the program that it should compress such that it has the same colourmap for all the images. In principle you could leave out this switch, but that is not recommended. Your movie will look awful.

The switch -max <max num of colours> gives the maximum number of colours the final movie can have. The recommended value to use is -max 200. Do not give a higher number than 220.

Please note the space between the name of the movie and the minus-sign.

You do not have control over the name of the output file. The string conv_24to8_ is prepended to the name of the input file:

conv_24to8 -c w -m 200 - ugc12441_movie

produces a file conv_24to8_ugc12441_movie.kf (!) with the compressed movie.

4.3 Multiple Contour Images


The <MultibeamView> programme has special-purpose code to display two datasets, one as images and the other as contours. If you wish to display multiple images or cubes, you should use the <kvis> programme.

Intensity-Intensity Scatter Plots


Earlier in this chapter (4) is a brief description of how you can use the c key to compute and display an intensity-intensity scatter plot of two images. You may also use this facility to display a scatter plot of two channels from the same cube. Simply load the same cube in twice (i.e. using the Set1 and Set2 file browser buttons), and select the two channels, one from each cube. You will need to ensure that the Link Frames toggle is disabled.

If the Link Frames toggle is enabled, then the scatter plot is computed using the two frames which have corresponding co-ordinates for the frame dimensions. This is usually the desired setting when generating scatter plots from frames of two different cubes.

Note that when computing a scatter plot from two images with a different co-ordinate grid, the pixels from the unseen image correspond to pixels with the same world co-ordinates in the visible image. Thus, there is no need to regrid either of the images.

next up previous contents index Karma Home Page
Next: 5 Volume Rendering a Up: Karma User Manual Previous: 3 Viewing and Comparing

Richard Gooch
Tue Dec 26 15:27:11 PST 2006