How can I find the square footage of an irregular driveway?

Question

I need to know the square footage of a long, curving private road with two irregularly shaped adjoining driveways. I've printed out a bird's eye view of the property with Google, used the exact known dimensions of a house in the photo to establish the scale, then made measurements as best I can on the photo, which indicates the road total is about 6,000 square feet (the red box is about 235' wide and 300' tall):

Is some kind of online tool available that will give me a more accurate estimate? For example, by outlining a region the tool will tell me the area? Even a "pixel painting" program that lets me do a flood-fill then tells me the number of pixels used would work.

Answer 1

Approximately 9,800 square feet, assuming your drawing is accurate. I hastily colored in the image using MS Paint (not perfect, since JPG compression added a bunch of fuzzy grayscale values).

Then using MATLAB with the image processing toolbox:

width = 235; % establish scale parameters
height = 300;
img = imread('areatest.jpg'); % read image in 
bwImg = im2bw(img,0.5); % convert from JPG to binary BW
% find black pixels, divide by total image area, 
% and scale to square footage depicted in drawing:    
dwArea = sum(sum(~bwImg))/numel(bwImg)*width*height; 

You may be able to work this online, with the compile online website. However, I'm not sure if it can read in files from your hard drive.

Answer 2

Using the histogram function in photoshop your white inside area is about 11% of the picture and if you include your black outline 12-13%. You can do the math from there.