How to Create an Outline from a Photo Reference

We are not all gifted with the ability to draw what we see even though we are good watercolour artists, however this should not stop us from being able to get a reasonable sketch from a photo reference onto our watercolour paper ready to begin the painting process.

One of the simplest ways of transferring a photo image to our paper is to use the Frisk Tracedown product. This is like carbon paper but it is coated with graphic powder on the back so that any pressure on the front transfers the graphite powder to the watercolour paper. Sometimes though using a photograph makes it hard to see which are the important lines to transfer to the your painting paper and I have discovered a method that I would like to share with that makes the process even easier to do.


I have discovered a fairly simple sequence of actions to follow using the free GIMP graphics application that runs on MS Windows to create a clear outline from a detailed photo image. Once you have this clear outline from your photograph you can then decide which elements you need to trace so that the important features get transferred in the correct proportions and perspective – two areas that cause most of us the biggest problems when we are sketching out our initial drawing.

This is the reference image I used for this demonstration which is a photo I took of the Bombay Distillery near Basingstoke:

This is the sequence of steps to follow:

  1. Having loaded in your photo reference image Select Menu Filters – Edge Detect – Edge and that will produce this effect:
  2. Now you need to invert this image so select Colours from the menu and then Invert and you will get this effect:
  3. Finally I have found it best to convert this image to a more black and white version for clarity by choosing Colourize from the Colour menu option and then in the popup dialog move the slider across to the left and position it half way down so that you end up with this:
  4. This is now a good clear outline to work with and makes it easy to pick out the important lines to transfer to your watercolour paper.

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Alternative to Gator Board

Gator Board Alternative

I have been investigating the availability of Gator Board, which is readily available in the US but not here in the UK. This board is very handy for stretching watercolour paper using the stapling method. The only outlet I can find that supply Gator Board is Jackson’s Art Supplies!

I decided to see if I could find an alternative board that was readily available, inexpensive to purchase and that would allow wet paper to be stapled to it for stretching without the board warping during the drying process.

Firstly I tried a couple of the so called “Foam Boards” but as they are not coated top and bottom with a wood veneer they weren’t successful at all and they were very expensive options.

Next I turned my attention to a board that is made from used newspaper and cellulose called “Sundeala Pinboard”. This is primarily produced to be used as pin boards on the wall which is what attracted me to it. In the US they call this board “Homasote Baord” however it is a slightly different construction to Sundeala Board. Although this board worked well, is readily available and held the staples during the paper drying time, unfortunately it isn’t rigid enough to stop the paper warping the board! It is also a very expensive option to use, a small piece measuring 60cm x 30cm costs around £20.00.

However I have now experimented with Oriented Strand Board (OSB). It is a type of engineered wood similar to particle board, formed by adding adhesives and then compressing layers of wood strands in specific orientations. This board is quite dense and I was able to find an off-cut at my local hardware store that I purchased for £2.00 to try it out! I think that this board is probably the answer as it ticks all of the boxes as far as requirements go and most importantly it is much cheaper to buy. B&Q sell it in 810mm x 410mm x 9mm for just over £7.00 and this is large enough to make two 1/4 imperial sized stretching boards.

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Paper Stretching My Way

On the left are the 6 stages that I follow to build a simple paper stretcher that doubles up as the painting board too and if you mount a tripod quick release nut on the back of the MDF board it will also fix easily to your tripod for outdoor painting! You don’t have to use MDF board but I found this was light and easy to cut and work with. You can use thin plywood or even gator board for this.
My goal here was to make something on a limited budget that was both simple to build and yet practical to use and that would last me a while once built.

I found that I could get the wood as offcuts from my local hardware store for next to nothing so these boards became easy, quick and very cheap to build. I have built one for each size of paper that I like to use both imperial and metric so 6 in all and I built the whole lot in less that a day.

Step 1:
This image shows all of the required pieces to complete the stretching board.
On the left are the precut strips of sandpaper, I would recommend that 60 grade sandpaper is rough enough for this job. Any rougher than that and the damp paper can become embedded into the sandpaper surface.
At the top of the image are the precut wood strips which are flat underneath and have rounded corners on the top edges. The long pieces go all the way across the longest edge of the board and the shorter pieces fit between them so that the retaining clips are fixed on at the sides rather than top and bottom, as you will see later.

Step 2:

Here you can see that I have glued the sandpaper strips to the board itself. The other option is to glue the sandpaper strips to the underside of the wooden strips instead, this leaves the board as a clean and unspoilt board.
If you prefer you can staple the strips to either the board or the underside of the wooden strips – this is a good option and allows the sandpaper to be easily replaced if needed further down the line.
Step 3:

This view shows  how the wooden strips are arranged on the painting side of the board. You now have the choice of attaching some pieces of webbing to these wooden strips so that they become an integral part of the board or just have them loose ready to clip into place.
If you do want to attach them to the underside of the board then the next step shows how I accomplished this.
Step 4:

This view shows the underside of the board with the webbing strips in place and stapled into position. This is a simple process if you have a stapler that opens out flat so that you can use it like a staple gun driving the staples directly into the MDF board.
I like to attach my wooden strips in this way as each set is cut specifically for the board they are used in conjunction with. When you have a few of these boards lying around I found that it is good to keep everything together in this way.
It is also easier to attach the wet paper to the board when the wooden strips are attached to each edge of the board like this.


Step 5:

This view shows the board as you normally view it with the sandpaper strips in place and the wooden strips laying flat and ready to fold onto the top of the board over the web paper.
You can clearly see the sandpaper around the edges of the board.
So at this stage you would wet your paper either by placing it in the bath or sink and running water over it.
I prefer to lay the paper reverse side up flat on the prepared board and using a mop brush thoroughly wet the surface.
I normally wait a minute or so to let the water soak into the paper then I wipe off the excess and turn over the paper and wet the top surface in a similar manner.

Step 6:

After another minute or so when the paper has absorbed the water check that it is all evenly damp and then you are ready to fold over the wooden strips and fix the clips.
This image shows the clips in place and how the top and bottom wooden strips fit around the side strips allowing the clips to hold both in place at each corner.
After another couple of minutes if the paper cockles slightly release the clips, refit the paper pulling it gently onto the sandpaper strips and replace the wooden strips and clips once again.


Now you can either wait for the paper to dry or use a hair dryer to speed up the process which is what I normally do.

The whole stretching process is simple and straightforward and the thin wooden strips do not impede the painting process at all. Once the painting is finished and dry removal is simple too and the paper will be completely flat and ready for framing.

I hope you like this idea and find it as useful and reliable as I do. If there is any part of this process you don’t understand then I will be happy to try to explain it more clearly for you just leave me a comment below or send me an email my contact details are available on this website.

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