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How does the pixel size change after the aspect ratio is chaged ?

I am using NI PCI-1411 frame brabber card and the signal is RS-170 signal. According to the discussion on the website:https://www.cs.rochester.edu/~nelson/courses/vision/resources/video_signals.html.

It said"The aspect (width to height) ratio for typical RS-170 signal rectangle is 4:3. The vertical resolution of video is limited to 485 pixels, as determined by the number of scan lines. The RS-170 standard specifies the aspect ratio (ratio of vertical/horizontal dimensions) of the video display as 3:4"

The CCD I use is Hitachi KP-M1AN.Its number of pixels are 768(H)*494(V) and the pixels size is 11.64(um) * 13.5(um),sensing area is 8.91*6.67mm,Horizontal/Vertical TV resolution is 570/485

Here are my questions:

1.Now I gave a square object to CCD (The CCD is Hitachi KP-M1AN.CCD pixels size is 11.64(um)*13.5(um) and the ).According to the pixel size on CCD, the horizontal pixel numbers should be different with vertical pixel numbers.however, I notice the pixel numbers at both directions are same. So I wonder what is the "real" pixels size now after the ratio change ?

For example, here is a square object is 143um*143um and CCD pixel size is 11um*13um.And according to pixel size it must be 13 pixels * 11 pixels. But what I see now is 12 pixels * 12 pixels.

2.According to question 1, if the pixels size change owning to the ratio change.How does the NI software change the pixel size (I mean extend it or compress it.)

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