If you are going to work from a photograph in conjunction with the grid-method you will need to transform your photograph into a useful reference image.
The procedure I will describe works quite well and I have personally been using it for quite a while. As you get more experience you can easily adapt the process to your own needs and working style.
Note that the grid-method is a crutch and although it is a powerful help, you should keep on practicing your drawing skills without the grid, that is, drawing directly from life. Here then is the procedure:
* Step one consists of scanning the picture into your computer. Make sure you work with sufficiently high resolution.
* Step two consists of importing the scanned image into a graphics program and adjusting the contrast and/or brightness so you end up with the best possible presentation of your scene. If you are working with a color picture you should also, at this time, create a gray-scale version.
* Now you can adjust the size of your image so it matches the size you want your drawing to be.
For example, if you drawing sheet is 10 x 14 inches, your reference image should be about 9 x 13 inches. This leaves about 1 inch of space all around.
In other words, you should put some careful thought in how large your image should be taking into account surrounding white space and the manner of framing.
This is quite important if you wish to avoid having to redo your drawing half way through the process because you realize the picture is, e.g., too big for the size of your paper or it will not look good for the size of your frame.
* This is also the time to pay attention to your composition, i.e., the layout of the final scene, the relationship between the subject and its surroundings, and how much of the subject matter you want to draw.
* Next, if you want to use the grid-method, you can draw a grid onto the image. I often use a grid consisting of 1 by 1 inch squares. So for a 10 by 14 inch drawing you will have 140 squares to work with. Most graphics programs have the option to automatically draw such grid lines over an existing image.
Using a grid is an age old tradition and does not constitute "cheating". Michelangelo and Edgar Degas, for example, made frequently use of grids.
But you should also keep practicing without grids and draw directly from the real world. Here the sizes and proportions will usually differ from the ones on your drawing paper.
Later, when you get better, you can increase the size of the squares and eventually do without them altogether. Or, you may want to use a grid only in a limited number of places where things are really complicated. Sometimes all you need is a few help lines or a few points to give yourself more confidence. But, for now, you may want to rely on a complete grid. A grid is, after all, just the ideal tool to use when drawing from photographs.
* Finally, you can print the finished image. If the image is too large you may have to print it out in several separate parts. Once this is done you are ready for the next step, i.e., the line drawing.
Note that after you scanned the picture you are done with it. Be sure you don't loose it or damage it so you can return it to your customer in tact.
We just explained how to prepare a picture for use as a reference for your drawing. The process consists of value adjustments, enlarging the picture, adding a grid, and printing the adjusted image.