Hello, I'm new with IDL. I 'm trying to reproduce the following code to test a canny filter on a png 8 bit unsigned integer : http://www.exelisvis.fr/docs/CANNY.html This is how I modified the code in my case : img = READ_PNG(FILE_SEARCH('SoCor_062_2.png', /FULLY_QUALIFY_PATH)) filtered = CANNY(img) TVSCL, img, 0 TVSCL, filtered, 1 First, when I display the raw image with "TVSCL, img, 0", it shows a black picture frame instead of showing my image. Then, when I display the filtered image, I have an error : "Expression must be an array in this context: FILTERED". However, the example code from EXELVIS do not show the making of an array. I followed quite closely the example... Any help to arrange and make this code working ? Bye