# What are the min and max arguments to EdgeDetect?

What are the min and max arguments to EdgeDetect, for all methods and specifically "Sobel"? How do I find the limits or ranges of functions in the future? Or is it 255?

• See Image Processing for the basics on image representation. Generally, channels and threshholds have a range of 0 to 1. – Michael E2 Dec 23 '13 at 1:47
• You can find default values in the documentation: in the "Details and Options" section. It is most assuredly not 255 as Mathematica scales pixel values between 0 and 1. – bill s Dec 23 '13 at 1:48
• @MichaelE2 @ bill I think this could be a good question, as I think the doc of EdgeDetect is not very clear, and there DO be differences between a threshhold of 1 and 1.1. – Silvia Dec 24 '13 at 12:55
• @Silvia Interesting. I interpreted the question as primarily "How do I find the limits or ranges of functions in the future." There seems to be a lack of explanation of thresholds and EdgeDetect in the docs. – Michael E2 Dec 24 '13 at 14:47
• @MichaelE2 I always do some try-and-fail attempts when using some functions like EdgeDetect, I think they really need a more insightful documentation :( – Silvia Dec 24 '13 at 14:55

In EdgeDetect[image, radius, threshold], the radius is expressed in pixels, and the threshold corresponds to normalized pixel values (ie. in the range from 0 to 1).
• So, Real images are not normalized in general? Or just in this particular case? – Oleksandr R. Dec 30 '13 at 20:37
• The normal range for "Real" and "Real32" data type images is from 0 to 1. But these images can also hold values outside the 0-1 range. An example where it expected is LaplacianFilter that yields positive and negative pixel values. – Matthias Odisio Dec 30 '13 at 21:12