how to detect answers which student chose it in answer sheet

hi , i want steps to create program to detect answers from answer sheet ex : (detect that student chose 'A' in question '1' in attached image ) thanks in advance

Answer 1

[Image Analyst]

The steps are

1. Extract the red channel from the RGB image.
2. Align image so that upper left circle is at some known location, and lower right circle is at some known location.
3. Define a template that is a little square or circle.
4. Get a sub image from every one of the 5 columns in a row of circles.
5. Find out which one has the lowest mean - use mean2().
6. From the mean, assign an answer of A-E based on which column had the lowest mean.

[selection, theAnswer] = min(theMeansForThisRow);

Not too hard (actually, easy ) except step 2 might be a little hard if the images are not aligned already.

[Abdalla Mansour]

Thank you for your reply, can you give me more information or tutorial about step 2 and 3 please, and i will use this answer sheet if you have extra steps for this answer sheet , could you tell me ??

[Image Analyst]

Look up imregister(). Then get a list of all the 25 different columns, and 20 different rows. Then loop

% Top half:
halfWidth = 3; % Whatever fits.
for r = 1 : length(rows)
    for c = 1 : length(columns)
        subImage = grayImage(r-halfWidth:r+halfWidth, c-halfWidth:c+halfWidth)
        means(r, c) = mean2(subImage);
    end
end

and so on. Now you have the darkness of every circle. Now look at the means in groups of 5, which represent one question, and determine which circle for each question was darkened. Just think through it logically and the program will almost write itself.

Repeat for the second bottom half.

[AminaOsmanova]

Please could you help me too.I can`t compare detected answers with the actual answer key stored in an excel sheet. Please help me

[Image Analyst]

OK, how can I do that?

Read this link and then post your question along with your image and your code that you adapted from this question.