Photoshop one-on-one – How to remove the background of scanned artworks in preparation for a digital takeover
Positioning a traditionally inked line drawing over a digital background in Photoshop
Digital documentation is in a somewhat transitional state. Several well-proven and established methods are available to create digital line drawings, add sun-shadow transitions, or deal with surface elements that are not part of the decorative scheme but are equally essential information bearers. By this point, most of us have accepted that there isn’t a single epigraphic technique to overrule others. The documentation procedure of an ancient Egyptian monument, be it a tomb or temple, can take multiple years involving hundreds of drawings, many of which are at certain completion levels. Integrating the many "legacy" drawings (created by using traditional media) into one's digital workflow remains one of the ongoing challenges of the digital age.
The Epigraphic Survey is a perfect example for this practice as their drawings are often started and finished by different artists over the long course of the epigraphic procedure. Additionally, many of their earlier line drawings, inked on photographic enlargement using Rapidographs and India ink (a.k.a. the Chicago House method), have to be refined and finalized digitally. An excellent example of the amount of work that needs to be done with digital integration is described by senior Survey artist Susan Osgood in this case study. Of course, in order to digitally interact with a traditional drawing, it needs to be "digitized": either scanned or photographed in high resolution. With drawings larger than a flat-bed scanner's input area, one must segmentize the artwork, digitally merging each separate chunk at a later stage.
Rapidograph line drawing created on photo paper scanned as a greyscale image (left) and as a bitmap document (right)
One of the big questions regarding scanning artworks comes down to the format: should a drawing be scanned in greyscale or preferably in bitmap. In general, a high resolution (1200 dpi) greyscale rendition of the source material preserves the most data. Nonetheless, greyscale images are more extensive than bitmap documents as all pixels (including the "white" background) are accounted for. On the other hand, scanning in bitmap provides a much smaller file with cleaner results. However, inked outlines that are rendered with fuzzy edges in bitmap are harder to integrate into a greyscale environment. Overall, the best, most flexible result would be a combination of a greyscale image with either (1) white, (2) transparent, or (3) no background. In the following tutorial, we'd like to show you the main differences between these options explaining how to "detach" a scanned line drawing from its background.
Traditionally inked line drawing from the Small Amun Temple at Medinet Habu, scanned as a greyscale image and "cleaned up" by using the Levels Adjustment Layer
First, let's see the more straightforward, simpler method. Once the artwork is scanned and opened in Photoshop, one should make a copy of the original layer (CMD+J) to make sure to have a reference point. Once duplicated, the simplest way to alter both line drawing and background is by creating a Levels Adjustment Layer right above it. Levels can do miracles over the scanned image, quickly providing us with the desired result. To make the brush strokes appear darker (ideally black), all one has to do is move the left slider towards the right in the Properties window. Similarly, to make the background appear lighter (ideally white), the right slider needs to be pulled towards the left. The mid-tone slider (in the center) is our best friend to balance these effects and create a black line drawing over white background with the least amount of deterioration. As you can see above, one can get relatively far with such simple modifications.
Naturally, although the background now appears to be gone, it is not transparent by any means, which can be quickly confirmed when trying to work on a layer set underneath the scanned image. To see what is below the line drawing, we must change the layer's behavior by selecting Multiply from the layer's panel on the right. What happens is that Photoshop takes the colors from the layer that's set to the Multiply blend mode and multiplies them by the colors on the layer(s) below it, then divides them by 255 to give us the result. It may sound overly scientific, nevertheless, what one should remember is that this process doesn't delete the background. As soon as the scanned drawing is positioned over a photographic image, this process's shortcomings become apparent by the halo created around the scene.
A seemingly transparent greyscale line drawing creates a halo over the image when added above a photo background that is somewhat opaque
Deleting certain pixels using Color Range
There is a far superior method to create genuinely transparent backgrounds by involving a bit of Photoshop magic. To remove a scanned line drawing's background, one needs to use Photoshop's Color Range tool. This tool selects a specified color or color range within an existing selection or an entire image. Just like before, the process starts with creating a copy of the scanned image layer by going to the Layer Panel and duplicating the background layer by pressing CMD + J. With the new layer selected, we have to create a Levels Adjustment Layer right above it and play with levels until the background is as white as possible and the line drawing is as close to black as desired.
Now go to Select / Color Range. Make sure, Sampled Colors are active, so the Eyedropper is enabled to pick sample colors from your image. If your image background still appears somewhat uneven after applying the levels tool or you don't want to lose too much detail on the line drawing, select Localized Color Clusters to build a more accurate selection. Next, make sure Color Range previews the Selection. By default, white areas are the selected pixels, and black areas are unselected, while grey areas are only partially selected. To sample colors, position the Eyedropper over the background area as shown on the photo below, and click to sample the hues you want to be included (this inclusion is temporary, in fact, we are selecting the color range that we'd like to delete from our drawing). Finally, we have the option to adjust the range of colors selected using the Fuzziness slider or by entering a value. The Fuzziness setting controls how wide a range of colors is in the Selection and increases or decreases the amount of partially selected pixels (grey areas in the selection preview). Set a lower Fuzziness value to apply restrictions to the color range or a higher value to increase variety. With the levels adjustment layer applied, setting Fuzziness to about 40 usually provides an ideal range for scanned line drawings; however, one might want to experiment to get the desired result.
With Fuzziness set low, sampling from the background selects all the pigment values that are close to white
There are a few options to preview our selections before hitting OK. The drop-down menu at the very bottom of the Color Range panel allows to see the actual selections of pixels in Greyscale, Black Matte (the best option for regular sun-shadow outline drawings), White Matte (only suitable for dark images, therefore not ideal for line drawings) and Quick Mask (showing unselected areas with the usual mask overlay). All in all, selecting background pixels through the Color Range window is a pretty straightforward affair with lots of control over the result. We can also save our settings before accepting the changes to apply the same settings for future projects.
Upon hitting enter, the familiar "marching ants" selection ribbons appear around each area with a value other than white. This is the best time to revise the decisions we made earlier and see if there are any details left out of the line drawing. It is advised to take a closer look around less prominent areas, such as damage or plaster textures.
Background area selected on a grayscale line drawing (left) with an extreme close-up showing the way Color Range deals with scanned Rapidograph ink marks (right)
Like with other, more common selections, there are options to add to and deduct from the background area. If any portion of the drawing falls within the selected area that you'd like to preserve, you can initiate small refinements. Once all look good, the whole selection must be inverted to reflect to the inked drawing. It can either be achieved by a shortcut (SHIFT + CMD + I), by going to Photoshop's Select Menu and picking Inverse from the list, or by clicking on the right mouse button while the Select Tool is active and hitting Select Inverse.
In the next step, we have to separate the inked outlines from the background. With the Select Tool active, click the right mouse button (CTRL + click) while the Select Tool is active and hit Layer via Copy. As a result, a new layer appears at the top of your layer stack containing only the outline drawing on a transparent background.
Playing around with Photoshop background options on the Preference pane
To make sure everything is as it is supposed to be, go to Preferences / Transparency & Gamut and change the grid size to any versions of Photoshop's signature checkerboard design. With the grid activated and all the other layers hidden, the line drawing should appear above this checkerboard pattern.
In the end, the scanned greyscale line drawing appears separated from its original background, as indicated by the grid shown underneath
We are done for now; the line drawing is separated from the background. There are multiple useful follow-up procedures to this process, the most obvious among them being the reuse of the line drawing as part of more complex artworks. Regarding our sample drawing (MHB 125L from the Small Amun Temple at Medinet Habu, drawn by Susan Osgood), the detached line drawing was dropped onto an elaborate composite photographic background based on a large wall segment of the north wall in Annex R. This backdrop (created by joining multiple traditionally or digitally inked drawings above the photogrammetric image) is going to be the master background for a color-enhanced digital drawing representing the Ptolemaic decorative phase of the temple's exterior.
The detached MHB 125L line drawing as part of the north wall in Annex R (detail, photographic background created by Owen Murray)
Of course, with the original background pixels gone, one doesn't necessarily have to stop at the line drawings' mere importing. We can take the liberty and experiment with new background options, tailoring the drawing's appearance to our publishing needs. For example, by adding a grey background (create a Solid Color Adjustment Layer and move it below your drawing) and altering the line drawing's coloration (using different blend modes), the drawing suddenly becomes more suitable for presentations set up in dark rooms. The results provided by the above method should suit both artist and publisher looking for better integration of traditional artworks into the digital environment.
Adding a Solid Color Adjustment Layer to the drawing to set up a grey background