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# 11 Superimposing Images

The <kvis> programme allows you to display different images on top of each other, while each image has a different colour coding. This can be used to display amplitude and phase together in one image, or compare different channels from a data cube by superimposing them.

These visualisation techniques require a 24-bit display.

# 11.1 Image and Contours

Note that there is another way to superimpose images which involves drawing one image as a greyscale or false-colour image and the other is drawn over the top as contours. This can be done with <kvis>, and does not require a 24-bit display.

You may also use the <send-contours> programme to draw contours over any image. This programme is a command-line tool, however, and is not normally used since the the GUI tools are much easier to use.

# 11.2 Hue and Intensity

With the program <kvis> you can superimpose two images, where one image is taken to control the intensity and the other the colour. This can be used to display amplitude and phase together in one image, or line integral and a velocity field.

To display the images run

`kvis`

First load File1 and File2. You should now see the combined images. The sliders Start Hue and Stop Hue manipulate the colour of the image, the sliders Minimum Intensity and Saturation the intensity.

By default, File1 will control the intensity, and File2 the hue. You can swap this by choosing ``Phase, Amplitude'' from the RAW DATA FORM menu. If you select ``Real, Imaginary'' then a rectangular to polar transformation of the data is performed, where File1 is real image and File2 is the imaginary image. You can swap the sense of this by choosing ``Imaginary, Real''. After the rectangular to polar transformation, the amplitude value will control the intensity and the phase value will control the hue.

A screen snapshot is available here

# 11.3 Intensity and Intensity

Another possibility is to overlay images so that all images are coded as intensity but in a different colour. This you can use to overlay two or three different channels of a data cube and inspect subtle differences. The <kvis> programme can be used to do this.

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