I was reading into the specs of my camera, and in the manual it says that the sensor I am using (SONY EMX287) uses 6.9 μm pixel size, making it a sensor with high spatial resolution. So I was wondering what does this mean? I thought that the size of the pixel depended on the working distance and the FOV, that is if I take a picture of something 3 m away vs 10 cm away, in the first case my pixel size will be much bigger. So what is this pixel size of the sensor computed with respect to?
The pixel size which is mentioned in the size is the size an actual physical pixel has on the sensor itself. So it gives the size the pixel takes in silicon on the sensor.
What you are talking is the area the pixel would cover in an image but the physical size of the pixel on the sensor will always stay the same no matter the FOV or working distance or any other things.
The word digit translates to a number, like 1 or 2 or 255 etc. Our fingers are also called digits, we learn to count on our fingers. Digital technology fractures the picture you are about to take into millions of tiny specks. Each speck, now called a picture element is assigned a numerical value based on its intensity as to its redness, greenness, and blueness (the three light primary colors). We abbreviate picture element by substituting the word “pixel”. This paint-by-number scheme records and saves pictures by converting them into series of numbers. When you view or print this picture, the software of the camera or the printer or the digital display (computer or TV) notes each pixel value and converts these values into glowing points of colored light or dots of ink/pigment on paper.
The specification you are asking about tells us the size of the pixels that covers the imaging sensor chip of your camera. Bigger is better! The more pixels that can be arranged on the surface of this chip, the higher the picture quality.