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I hope this is the correct place to ask this. If not, please refer me to a better place, thanks. Now to my question,

I am learning about digital image processing, and the book I am reading is discussing spatial resolution. They discuss spatial resolution in terms of line pairs. They talk about constructing a chart with pairs of dark and light lines, and how the width of a line pair is the width of a light and dark line. This is all of the information the book gives about line pairs, and I don't really understand what role these play in digital image formation and resolution.

What does a line pair actually correspond to or respresent in the context of image formation, specifically in a camera? There is a question in my book about how many line pairs/mm a camera will be able to resolve when taking an image of a subject. It gives the size of the CCD in the camera, as well as how many elements there are vertically and horizontally in the CCD. What does line pairs/mm of the CCD mean? Is this something like the number of pixels that will be resolved per CCD element? It just isn't clear to me how line pairs are realized in the camera.

I hope this question makes sense. I am a CS student so don't do much of anything with signal processing, but I would like to have a better understanding of how images are formed with respect to their spatial resolution capabilities.

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  • $\begingroup$ yes this is a right place to ask that... $\endgroup$ – Fat32 Sep 24 at 22:26
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The spatial resolving capability of an optical system refers to its ability to distingusih between closest (and possibly tiniest) details. The distance between a pair of lines, yields a measure of how small the distance between them can be while they are still sperated from each other. Resolution depends on several factors such as brightness level, color, and environment.

Those resolution (line) charts are designed to test optical equipment and systems, including your eyes too. Consider two black lines (with some thickness) viewd at some length and let them come closer under your control. It's known that at some small distance, you can no longer tell that there are two lines, but they will seems like a single one. That distance is the limit of your optical resolution. To get rid of the viewing distance dependence, the resolution can often be stated in a spatial angle unit.

That's also true for a camera system. It's spatial resolution is limited by two factors; first the resolution limit of the lens (its sharpness), and then the resolution limit of the CMOS / CCD sensor grid (its sampling density).

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  • $\begingroup$ Ok, you've cleared up the concept of line pairs for me. However I am still a bit unclear about how this works in a CCD. Right now it seems to me that essentially a higher ratio of line pairs/mm, all else constant, results in more line pairs being seen by each element of the sensor? I don't think I am right. $\endgroup$ – Blake F. Sep 25 at 14:53

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