Grey Scale Stenciling Step by Step

Start by selecting a source image

This one was found on google images by searching for banana

Open the image in GIMP/Photoshop etc

Crop to 4:3

Resize to 160x120 or 120x160

Change the colour from RGB to greyscale

It should look like this now

Change the colour from greyscale to indexed colour, choose, 8 colours and dithering turned on

It should look like this

This is where it gets a little tricky

for each colour of grey we want to make a square of increasing size to show how dark it is

I have written a little program that does this,if you really want I can do this step for you

see the previous post

here is the output as a PNG and PDF

PNG

PDF of Banana all filled in

The trick is now to enlarge this image to be as big as your canvas

There is a neat tool called "Poster" which is part of Linux UI package KDE, if you arent familar with command line tools the stuff below will seem like it is in a foreign language

Usage: poster  infile

options are:
   -v:         be verbose
   -f:         ask manual feed on plotting/printing device
   -i:    specify input image size
   -c: horizontal and vertical cutmargin
   -w: horizontal and vertical additional white margin
   -m:    media paper size
   -p:    output poster size
   -s: linear scale factor for poster
   -o:   output redirection to named file

   At least one of -s -p -m is mandatory, and don't give both -s and -p
    is like 'A4', '3x3letter', '10x25cm', '200x200+10,10p'
    is either a simple  or %

   Defaults are: '-mA4', '-c5%', '-i' read from input file.
                 and output written to stdout.

So with a bit of luck you can get this to produce say a 4x4 grid of a4 sheets that you can print on a standard laser or inkjet

I have attached the sample PDF for the bananas

Feel free to print out 18 pages : PDF of the tiles of the poster

Using the grid references in the corner you can arrange the tiles

the little cross hairs will help you line it all up

If you wanted to cheat you could use this for paste ups

But if you want stencils then is the labourious bit

Printing onto transperancies, cutting out all the squares

If you made a tool of each square size as a punch you could save some time

Then spraying aerosol enamel paint through the squares onto canvas or whatever

You get too cut out 19200 squares, woo hoo!