User manual

specifying explicitly in the control band. If you click on the “use Aladin autocut algorithm”,

Aladin will proceed again with its autocut algorithm without looking for meaningful

pixels in between the limits you indicated. If the check is not activated, lower and upper

threshold will be taken as specified. The button “Reset” is a short-cut to get all the image

dynamics back.

Modifying the initial threshold treatment is a long process (a few seconds,

proportionally to the image size) while a simple contrast change by modifying the

contrast function is almost instantaneous.

Specific images, specific cases

If dealing with real colour images or with a data cube, the window is adapted to the data

type.

Colour Image

Aladin can deal with “real colour” images (coloured compositions -- see 5.9, JPEG, GIF,

PNG or colour FITS images). In such a case, there is not automatic threshold and the

dynamic control window shows 3 histograms one on top of the other, with control slides

corresponding to the distribution of pixel values in the 3 red, green, blue components.

Each component has its 3 control cursors, as for a usual image. Holding the SHIFT key

while moving the cursor will synchronize the 2 other colour components in order to do a

simultaneous adjustment on the 3 components.

Image data cubes

Aladin can let you manipulate image data cubes (see 5.10 – image associations or FITS

cubes). In this case, the histogram of the pixels distribution is related only to the

currently displayed image. If the display is currently going through the cube, the