bim = bigimage('tumor_091R.tif');

h = bigimageshow(bim);
hROI = drawcircle(gca,'Radius',470,'Position',[1477 2284]);

maskLevel = 3;

ref = bim.SpatialReferencing(maskLevel);
pixelExtent = [ref.PixelExtentInWorldX,ref.PixelExtentInWorldY];

bmask = bigimage(ref,1,'logical');

for cStart = 1:bmask.BlockSize(2):ref.ImageSize(2)
    for rStart = 1:bmask.BlockSize(1):ref.ImageSize(1)

        % Get the center of top left pixel of this block in world units.
        xyStart = [cStart,rStart].*pixelExtent;

        % Get the block size. The |'BlockSize'| property represents the
        % size as a 2-element vector of the form [row,column]. Switch the
        % order of the elements so that the block size is represented as
        % [x,y].
        bsize = bmask.BlockSize;
        numRows = bsize(1);
        numCols = bsize(2);

        % Determine which pixels have coordinates inside the ROI.
        roiPositions = hROI.Vertices;

        % Transform |roiPositions| from world coordinates to the intrinsic
        % image indices at the given resolution level.
        roiPositions = (roiPositions - xyStart) ./ pixelExtent + 1;

        blockMask = poly2mask(roiPositions(:,1),roiPositions(:,2), ...
                              numRows, numCols);

        % Set the pixel values of the block.
        setBlock(bmask,1,xyStart,blockMask);
    end
end

figure
bigimageshow(bmask)