Determine a regions average in MATLAB

Question

I need some help with RGB capture in a image. I am using impixel to manualy get RGB from a picture, but i would like to create a grid of let\'s say 20x20 px boxes where it will

Answer 1

This is my complete code for automatic color grabing from pictures in folder. So the program asks you to chose a folder and after that you get a table full of information about color and roundess. I am using this code to get color from fruits that have white background . It does everything by itself. Hope it helps someone.

clear all;
clc;


uiwait(msgbox('Chose the folder where your pictures are kept. Click OK to continue..'));

% Opening the folder

folder = uigetdir(pwd); 
filePattern = fullfile(folder, '*.jpg');
jpegFiles = dir(filePattern);
    for k = 1:length(jpegFiles)
        baseFileName = jpegFiles(k).name;
        fullFileName = fullfile(folder, baseFileName);
        [pathstr, name, ext] = fileparts(fullFileName);
        naziv_voca=name;

        %Taking RGB color

        slika = imread(fullFileName);
        [redovi stupci RGBboje] = size(slika);
        red_ink = floor(redovi/10);
        stup_ink = floor(stupci/10);
        r = 1;
        c = 1;
        for stupac = 1 : stup_ink  : stupci
            for red = 1 : red_ink : redovi
            red1 = red;
            red2 = red1 + red_ink;
            stupac1 = stupac;
            stupac2 = stupac1 + stup_ink;
            red2 = min(red2, redovi);
            stupac2 = min(stupac2, stupci);
            crveniS = slika(red1:red2, stupac1:stupac2, 1);
            zeleniS = slika(red1:red2, stupac1:stupac2, 2);
            plaviS = slika(red1:red2, stupac1:stupac2, 3);
            crvena(r,c) = mean2(crveniS);
            zelena(r,c) = mean2(zeleniS);
            plava(r,c) = mean2(plaviS);
            r = r + 1;
                if r >redovi
                    r = 1;
                end
            end
            c = c + 1;
                if c >1
                    c = 1;
                end
            end

        RGB=[crvena,zelena,plava];
        bijela=[255 255 255];
        tolerancija = 50;
        rez = RGB((abs(RGB(:,1)-bijela(1)) > tolerancija) | (abs(RGB(:,2)-bijela(2)) > tolerancija),:);
        trez=round(rez); 


        %Taking shape

        pic = rgb2gray(slika);
        threshold = graythresh(pic);
        bw = im2bw(pic,threshold);
        fbw = ones(size(bw))-imfill(ones(size(bw))-bw); 
        invImg = ~fbw;
        f = bwlabel(invImg);
        S = regionprops(f,'Area','Perimeter','centroid');
        Thr=100;
        S=S([S.Area]>Thr);
        score = (min(sqrt([S.Area]),[S.Perimeter]/4)./(max(sqrt([S.Area]), [S.Perimeter]/4))).^2;
        score=max(score);

        %Inserting data into table and creating data

        if exist('tablica.mat','file')
            vel=size(trez,1);
            for z=1:vel
                s=load('tablica');
                olddata=s.data;
                temp=trez(z,:);
                dataCell= [naziv_voca,num2cell(temp),num2cell(score)]; 
                data=[olddata;dataCell];
                save('tablica.mat','-append','data');
            end
        else
            stupac_rgb = num2cell(trez,1);
            zstupac = cellfun(@sum,stupac_rgb); 
            zred = size(trez,1);           
            rez = bsxfun(@rdivide,zstupac,zred); 
            trez=round(rez);
            data= [naziv_voca,num2cell(trez),num2cell(score)];
            save('tablica','data')
        end 

    end  
    uiwait(msgbox('Your information is saved'));

Answer 2

Depending on your exact needs I see two solutions:

Downscale the image using impyramid(img, 'reduce'). This gives you a smaller image consisting of average values of the original image. Then do what you did before to access single pixels. Repeat as often as necessary to get 2x2, 4x4, 8x8 or larger "boxes".

Or you could use define a box (or arbitrary shape) as a matrix of ones and zeros and use the regionprops function in order to get information about the images content depending on the fields containing ones:

roi = zeros(size(img))
roi(1:10,1:10) = 1;
r = regionprops(roi, img, 'MeanIntensity')
average = r.MeanIntensity