Stacking

Before proceding with the stacking process be sure all images have been aligned (see Images alignment) and then click the 'stack' button in the 'Tools' section.

A dialog window will be shown in which you can select the stcking method:

Currently the following stacking method are available:

WARNING: The 'native' stacking methods use algorithms that can store data directly to the RAM, the others instead MUST store data to temporary files (see impostazioni) in a folder that is '/tmp/lxnstack' by default. Due to the use of 32bit or 64bit float point numbers, the temprary files can be very big. For this reason you must assure you have enough space on the disk where the temporary folder is located (or enough free RAM if native methods are used).

Here an example of the average of some images.

Once the stacking is completed, you can adjust the output level of the result image by clicking the 'Image levels' image in the 'Tools' section. The following dialog window will appear:

On the right side of the window the histograhm of the result image is displayed and on the left side there are the curves controls to adjust the levels of the image[4]. If the 'data clicking' section is enabled you can choose if to 'clip' pixel valuex outside the specified data range ( [0,255] or [0,65535] ) or to 'scale' the image levels in order that the maximum and minimum values are contained in the specified data range.

To explain how the curves work, we use the notation previously introduced in the section 'Zoom and Display'. So let I be the matrix of size WxHxC where W and H are the width and the height of the image and C the number of components. Now if I(x,y,c) is the element of I at position x,y,c and F(X) the curve to apply to I, then the result image I' is I'(x,y,c)=F(I(x,y,c)) for each x,y,c.

Now if we introduce the parameters A,B,O,M,N, the following curves can be defined:

The image shown below is the above one to which a Power curve is applyed.

WARNING: Lxnstack is NOT an image editor. The level adjustment functionality provided only to obtain a better image to pass to other image-editing programs and reduce so nasty unwanted artifacts.

lxnstack © 2013 Maurizio D'Addona