Someone posed the question to me, if they could use their scanner for grading multiple choice tests. This is for someone in a volunteer teaching position in one of the less advanced, poor countries, but they do have an image scanner available. So I'm not a real expert in graphics manipulation and analysis, most of what I do in the way of graphics is generating print images for books, so I mostly use ImageMagick to help with some of the manipulations, but they are simple... crops, resizings, adding margins, and the like.
In thinking about the problem I see several steps, and several possibly applicable uses of ImageMagick. Scan the answer sheet, which would be a bunch of pencil filled dots. The locations of the dots would be known. Perhaps a preprinted dark stripe or two would be good for alignment? Or even a surrounding box? Is there a way to detect, and then rotate and translate known objects to a fixed position, to compensate for misalignment of the papers in the scanner? This seems to be the hardest thing, maybe because it is the part I know least about. The scan could be done in color or greyscale, and then thresholded to eliminate erasures... the use of soft, very black pencils is the norm in those testing environments. Then, knowing where the answer dots would be, one would check for the overall darkness of the enclosing region, and if it exceeds some threshold it is considered marked. Once the set of marked boxes is known, the actual scoring, or grading, is straightforward logic. The test creator would simply supply a list of "correct answer" boxes, possibly a weighting for certain "partially correct answer" boxes, and others would be assumed "incorrect answer" boxes. Some rules about whether or not multiple boxes are allowed or required to be a "correct answer". Multiple choice doesn't only mean one choice, always. So the grading rules might be complex, but that is orthogonal to the "marked box detection", which is the part I'm concerned with here. Does anyone have advice, or sample code, on how to approach the first part, the alignment? I think I understand enough to do the remaining parts, as well as understanding how to generate the form that would be printed to be the answer sheet. Or maybe this is a solved problem, that I have missed in my searches. I found lots of paid solutions to this sort of thing, but didn't find a freeware, or low-cost shareware, but maybe there was one hidden in the noise. I'm not averse to using something besides ImageMagick if it exists as a canned solution, but if I need to create my own, then ImageMagick seems like a good starting point overall, and if I can figure out how to do the scan alignment. Glenn _______________________________________________ Magick-users mailing list [email protected] http://studio.imagemagick.org/mailman/listinfo/magick-users
