The Greyramp Tool

Greyramp Tool

Greyramp Tool

The greyramp tool is a little separate window, which is used to control the contrast mapping for the display of the gel images.

The window has two triangular sliders at the top and bottom, which can be dragged left and right to adjust the minimum (bottom) and maximum (top) edge of the so-called greyramp. The red square in the middle can also be dragged to shift both sliders at the same time.

The greyramp is a simple linear mapping of the range of possible values (0 - 255) into a smaller range between the minimum and maximum. It also means that a reverse mapping will invert the image on the screen. This happens when the minimum value is bigger than the maximum.

Pseudo-colour displays

A monitor said to use pseudo-colour graphics, if their display buffers are 8-Bit deep. Such systems use an indirect colour system, and although they can potentially show 16 million colours, only 256 of them can be displayed at the same time. To facilitate this, the graphics system maintains a colourmap, which is used to map the ideal colour of a particular pixel to one of the 256 colours that the system can show at the moment. On an 8-Bit display, the greyramp tool simply adjusts this system colourmap when you drag the sliders. Hence on such displays the greyramp tool is highly interactive.

High-colour displays

More modern displays have display buffers with more and more memory, and displays with 16-Bit and 24-Bit graphics are becoming more and more common. Image is now able to display gel-images on those displays too, but the greyramp tool behaves slightly differently.

On 8-Bit displays it is simple to adjust the contrast of the image, only the system colourmap needs to be changed. High-colour displays do not use such a colourmap, because they can always display all possible colours at the same time. To make contrast adjustments, the actual image needs to be re-rendered to change the colours of all of the pixels. Especially when large images are displayed this may take a while each time, therefore the sliders on the greyramp tool are not as responsive and interactive as on 8-Bit displays.

It is recommended to run the Image program on the same machine where the X-server is running, to make sure the maximum transfer speed is used for the graphics display.

Last modified : November 1999 Image 3.10

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