Line drawings - using Photoshop to clean up photographs of line drawings
I often need to clean up line drawings of artefacts and sketches - the originals are typically from pdf files, and of poor quality. This method using Photoshop allows me to make much better images than the originals, especially when combined with first making the drawings a lot larger.
We start with the original photo, taken in a museum. The line drawings here happen to be in inverse, white on black, and are behind glass, as is normal, with reflections, as is also normal.
Photo: Ralph Frenken 2015
The first step is to straighten the image. Click on the crop tool in the tool box, and a 'straighten' icon appears on the menu above the photo. Click on this 'straighten' icon, and drag the cross hairs across the photo on a line you wish to have horizontal or vertical.
You can enlarge the cropped area by dragging the handles now if you wish.
Double click to confirm, and for the image to be cropped.
Open levels, command L on the mac. Otherwise use the drop down menus:
This graph appears.
You will be moving the outer two arrows below the graph to alter the image, darkening the dark areas to black, and lightening the light areas to white, as much as possible.
Invert the image if necessary, using either Command I, or Image...Adjustments...Invert.
We are getting closer to the desired result, but in this case the lines are a bit fuzzy, and need to be more solid and darker.
Remove any unwanted spots on the image with the eraser, and see if another go on the Anisotropic command helps the image. The lines tend to get thicker as you use this command.
The edges are much improved after this step.