How shadows can be created and what effects they have on scanned images
A shadow is a dark area where light cannot reach, but when scanning an image, light can’t get to the scanner either. When you scan with shadows in a photograph, it’s called a “light leak”. There are various ways to scan without shadows, including (1) with the light source at your back, or (2) scanning from the inside of a “scanner box”. Instead of filling in it with black (as is normally done), we’ll use our knowledge of physics and mathematics to get rid of the shadows.
To do so, we can use the following equation:
where formula_2 is the intensity of light in the image (the original image), formula_3 is the intensity of light from our light source, formula_4 is a constant and formula_5 is the grey level at position X and Y. In this case, we can write:
The solutions for formula_7 and formula_8 are:
We can change this to the standard system of equations by using the following equation:
This will give us exactly the same solutions as we would have had if we wrote our equations in the standard system, only concisely. If you look at our original equation (Reguła 1.5) from the standard system, you’ll see that we have formula_11. The equation will also work for these two equations:
Now, if you look at our equations in the standard system again, you’ll see that we had formula_14. This will also work for these two equations:
The best ways to avoid shadows when scanning an image
Any method to avoid shadows will have disadvantages. For example, if we use a scanner box (also called a “scanner tent”), we can scan with even more precision. But the shadows will still be there. The same is true of a scanner tent that uses a light table inside. Here’s the best way to scan without shadows. It’s only necessary if you plan to produce a print from your scan.
Why Shadows Are Bad for Your Image
Why are we so concerned about shadows? First, they are bad for your image because the image will have an odd, patterned shadow on one side (or both) of the subject. The shadow is annoying, but it’s also distracting. If you were looking at that picture as a print on a wall, you’d see that patterning and it would pull your attention away from the subject of the photo.
Examples of how to scan without shadows using different software programs
For this example, we’ll use Photoshop. Here are three ways to scan without shadows in Photoshop, using a light source at your back. We’ll start with the simplest way and then move on to the more advanced way. All of them will remove shadows, but you’ll have to decide which method is best for you. Here’s how it’s done:
The Easy Way (symmetrical light)
When you have even, symmetrical lighting from a window, or from a light source behind you, this is the easiest way to scan. The scanner will be able to see the entire document evenly and all shadows on the document will be removed. You won’t need to crop as tightly as if you have uneven lighting/bright areas on one side of your page. Here’s how to do it: