Valid indices are restricted in parlor loop

Is anyone able to help me understand how to format my arrays so I don't receieve this error. The error arises when I try to fill portions of my "CD8_image" zeros array with values inside the parfor loop.

region_width = width_end - width_start + 1; %fence post
region_height = height_end - height_start + 1; %fence post
interval = 2000;
number_x_tiles = region_width/interval;
number_y_tiles = region_height/interval;
CD8_image = zeros(region_height, region_width);

parfor i=1:(number_x_tiles)
    frame_x_start = width_start + interval*(i-1);
    frame_x_end = width_start + interval*i - 1; %fence post
    for j=1:(number_y_tiles)
        frame_y_start = height_start + interval*(j-1);
        frame_y_end = height_start + interval*j - 1; %fence post
        I1 = imread('CD8.tif','PixelRegion',{[frame_y_start frame_y_end],[frame_x_start frame_x_end]});
        contrast_I1 = histeq(I1); %increase contrast
        R_I1 = contrast_I1(:,:,1);
        B_I1 = contrast_I1(:,:,3);
        mask1 = R_I1 > B_I1 & R_I1 <160 & B_I1 < 40; %mess with these for red
        F = medfilt2(mask1); %filter 1 (noise1)
        F1_I1 = wiener2(F,[3 3]); %filter 2 (noise2)
        F2_I1 = medfilt2(F1_I1); %filter 3 (noise1, try2)
        F3_I1 = bwareafilt(F2_I1,[200 5000000]); %filter 4 (size) 
        height_1 = interval*(j-1)+1;
        height_2 = interval*j;
        width_1 = interval*(i-1);
        width_2 = interval*i;
        CD8_image(height_1:height_2,width_1:width_2) = F3_I1;
    end
    frame_y_start = height_start + interval*(j-1);
    frame_y_end = height_start + interval*j - 1; %fence post
    I1 = imread('CD8.tif','PixelRegion',{[frame_y_start frame_y_end],[frame_x_start frame_x_end]});
    contrast_I1 = histeq(I1); %increase contrast
    R_I1 = contrast_I1(:,:,1);
    B_I1 = contrast_I1(:,:,3);
    mask1 = R_I1 > B_I1 & R_I1 <160 & B_I1 < 40; %mess with these for red
    F = medfilt2(mask1); %filter 1 (noise1)
    F1_I1 = wiener2(F,[3 3]); %filter 2 (noise2)
    F2_I1 = medfilt2(F1_I1); %filter 3 (noise1, try2)
    F3_I1 = bwareafilt(F2_I1,[200 5000000]); %filter 4 (size)
    CD8_image((interval*(j-1))+1:interval*j,(interval*(i-1)+1):interval*i) = F3_I1;
end

Answer 1

[Walter Roberson]

You cannot do that. Output arrays must be indexed in very simple ways, never as a range computed from the loop variable.

You can reorder the output to be tile height by tile width by number of tiles and write into (:, :, tilenumber) and then after the loop permute and reshape as needed. Or you can reorder to tile height by tile width by number of y tiles by number of x tiles, and inside the x tile loop construct a temporary 3d variable with the third dimension ordered by y tile number, and then after the y loop, write the 3d array into (:,:,:, x tilenumber), and then after the parfor permute and reshape as needed.