User manual

Access to the window
The window controlling the resampling can
be opened with the menu “Image =>
Resampling”. You need to select beforehand
the image to resample in the stack. In the
window, you need to specify the reference
image, whether you wish to keep or not the
“full” pixels, or just the “grey levels” code on 8
bits (quicker), choose the estimation method
for the pixel values and at the end, say
whether the original image needs to be
replaced by the newly sampled image, or kept
in the stack.
Attention: Please note that the resampling methods in Aladin do no preserve the flux,
i.e. the sum of the pixel values before the resampling is not the same as the one
afterwards.
Note:
Tip: Using the translucence of images (see 5.1) is a quicker and more flexible alternative
to resampling. It is however less precise since it does not act pixel-by-pixel, but only
based on the four corners and does a global approximation for the other pixels location.
5.12Arithmetic operations on images
Menu: Image => Arithmetic operations …
Image => Convolution
Image => Pixel normalisation
Addition, subtraction, multiplication and
division
Aladin offers a simple interface to compute simple
basic operations on a couple of images: addition,
subtraction, multiplication, and division. The
control window can be opened with the menu
“Image => Arithmetic operations” (accessed only if at
least two images are in the stack). Aladin will
proceed pixel by pixel by doing, if needed, a resampling of the second image so that it
corresponds to the grid of the first image (see 5.11). One can ask to do first a
normalisation of the pixels in the two images so that their values are located around 1 by
dividing by the pixel average. The result from the operation will be seen as a new image
plane in the pile.
Tip: If you wish to use a scalar as the second operand rather that an image –e.g. add a
given value to all pixels – you can use scripts commands: +, -, *, /(see 7.1)
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