User manual

The 256 pixel values can be displayed

either with grey levels, in positive or

negative, or with a colour table that

will make a correspondence between

each pixel value and a specific colour.

It is however possible that

“interesting” pixels are not those of

your interest, or that the autocut

algorithm is not well suited for the

characteristics of the images you wish

to display. To adjust manually the

pixels dynamics, you can use the

“Image => pixel contrast ’ menu, or the

“pixel” more directly accessible in the

tools bar.

The pixel dynamic window shows the

following:

 A strip showing how the 256 pixel

levels look;

 An histogram showing the pixels

distribution between the smallest

and the largest values kept by

Aladin;

 Three tuning cursors;

 And information and control band.

In a single click!

If you wish to only increase or decrease the image contrast without modifying the range

of kept pixels, you can modify the transfer function that was chosen:

 Log: a lot of contrast

 Sqrt: some contrast

 Linear: normal

 Pow2: little contrast

If you wish to refine the pixels dynamics, you need to read and understand what follows.

Information on pixels

At the bottom of the window, you will find information giving the minimum and

maximum values existing in the image, as well as the lower and upper thresholds

estimated by Aladin in an automatic way (“autocut limits”).

The curve over plotted on the histogram shows the transfer function that is used to

relate the retained pixels values and the 256 possible levels. By default, this is a simple

oblique line because 1) by default the conversion is a simple linear translation, and 2)

the colour table is “gray” - grey levels, i.e. all 3 components Red-Green-Blue effectively

displayed will always have the same values. A colour table using something other than

grey levels will display 3 distinct curves, one for the red, one for the green and one for