Here are some examples. I took a screenshot of this browser composition window after making that last post but before submitting it (yes, the browser has a built-in spell-checker).
I saved the image in the three formats under discussion. I left the JPEG "quality" at the software default of "75" and upped the PNG compression from the default level of "6" to "8" instead.
Then I displayed each in the displaying software and opened a magnifying window to the same magnification and at the same point in each image, placed the mag window over the original, and snapped another shot of them both, for each one. Then I grabbed a window showing the three original file sizes, cropped it to the same dimensions as the others, and tiled them into this one, attached.
The JPEG file is the largest, and note the loss of fine detail and the extra artifacts. The GIF and PNG files are almost the same size, but the GIF file is only 256 colors (the limit of the 8-bit format) while the PNG would have every color available in the 24-bit format.
Line drawings will be treated in like manner as this smoothed text was.
I don't know if a standard "homeowner" model scanner would treat the microfiche cards with their due respect, but doubt it. I'd guess some pro equipment would be necessary for the task, but don't let me discourage anyone from trying.
I should add that when I convert the 8-bit GIF file to PNG (using the default compression level), the result in indistinguishable from the GIF in appearance, but is only 10824 bytes.
Glen