I am an artist with an interest in signal processing. I realize that maybe this question very basic, but the web banner on the frontpage says "anyone can ask", so I assume that means beginners too.
I have been trying to wrap my head around the terminology related to unsharp masks, high pass filters, the Sobel filter, etc.
According to my understanding unsharp masks use a high pass filter. The high pass filter helps define areas of transition in pixel value. This also has the effect finding edges. The pixels which are next to pixels brighter than them get darker, and the pixels which are next to pixels which are darker than them get brighter.
A friend of mine mentioned the Sobel operator was used for edge detection. I understand the basic idea of the Sobel operator as being the image treated as a grid. A matrix is the math term I see used often. According to him, the Sobel operator finds edges by applying a darkening or lightening effect based on the pixels around it. This sounds very similar to the unsharp mask's use of a high pass filter.
When I look online I don't see Sobel techniques referred to as high pass. I see pages like this that explictly list out Sobel separate from high pass filters.
But then I find published research papers which describe sobel edge detection filters as being a kind of high pass filter.
To me, my friend's description of the Sobel method sounds a lot like the descriptions I find of the high pass filter. My friend says they are different and I'm not sure I understand how?
I think I need to clarify my question, since it's sort of a multipart question:
My questions are:
1) Is the unsharp mask using a high pass filter? Not IS it a high pass filter, but if it uses one.
2) Is the Sobel filter a high pass filter?
3) If it is, then what's the technical difference between the definition of the Sobel as a high pass filter and the high pass filter used in a digital unsharp mask?
I understand that digital unsharp masks are not high pass filters, but they do use them according to the signal processing pages I found.