To see the difference between RGB and s-video, you need to compare colours. That is, put for example blocks of red, green and blue (or any colours) next to each other in DPaint and look at how sharp the transitions of the colours are.
In s-video the luma channel (black and white) is certainly very sharp, but it is the chroma (colour) where things have lower resolution. In RGB it makes no difference what colour a pixel is, since all the data is transferred over separate lines.
I have made a comparison like this earlier. Open
these pictures in separate tabs in the browser, or download them so you can easily flick between the different images.
These are all captured from my Amiga, running Turrican II, nothing is from an emulator or otherwise altered. I used a USB device to capture composite and s-video and a PCI capture card for RGB.
You can quite well see how the composite image is blurry overall, while s-video is very sharp as far as the greyscale data goes, but the various colours on the uniforms blend to each other. In RGB mode the image is essentially flawless.
