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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.

Line drawings


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
Source: Musee-de-Prehistoire-Grottes-de-la-Marche-et-des-Fadets




Line drawings


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.




Line drawings


Crop the image to the size you need.




Line drawings


Open levels, command L on the mac. Otherwise use the drop down menus:

Image...Adjustments...Levels.

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.




Line drawings


Move the two outer arrows until you get close to the desired effect. Press OK.




Line drawings


You can repeat this process a number of times, getting closer to what you want.




Line drawings


Change to greyscale, using the series of dropdown menus:

Image...Mode...Grayscale




Line drawings


Once again you can move the arrows on the levels screen to get a better image.




Line drawings


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.




Line drawings


Move the arrows on the Levels graph again until the lines are blacker, and the whites whiter.

At this point the edges are still a bit fuzzy, but the lines themselves have improved a lot.




Line drawings


Go to Filter...Stylize...Diffuse...Anisotropic.

Press OK.




Line drawings


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.

Press OK.

The edges are much improved after this step.




Line drawings


Smart sharpen is often a good way to improve the image at this stage.

From the dropdown menu choose Filter...Sharpen...Smart Sharpen.




Line drawings



Et voilà!

You are done.







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