A step by step guide to removing the paper tone background from black and white illustrations using a global approach in Adobe Photoshop.
Our example for this article is an A2-sized original work on paper by our talented client Michael Polychronopoulos. We scanned it here on our dedicated A2+ sized art reproduction scanner imported from Germany.
This article outlines a near-universal approach to removing the paper tone from black and white scans, though as ever the quality of your initial raw scan is incredibly important to achieving a great result. No amount of editing in Photoshop can remedy problems such as insufficient resolution, out of focus scans or clipped highlights and/or shadows. Great art reproduction starts with a great scan.
Consider also whether you have the time and aptitude to put towards digitising and/or then editing the resulting raw scan files. High quality digital art reproductions rely on significant expertise being deployed over a number of steps. It's all do-able for the technically minded enthusiast, after significant practise and investment of time in developing your techniques - but it might not be for you. If not, consider our comprehensive Art Reproduction Service here at Image Science where our friendly team can advise, scan, retouch and print all your files to the very highest of standards.
For document scanning at home we recommend the Epson V600 (or V850 if you need a scanner that can also handle the scanning of camera film). Though for a considerably higher quality starting point, we recommend you use our raw scanning service - specifically offered for clients with the skills to retouch their own files, but not the hardware to digitise them in the first place.
If you are using your own scanner it is best to ensure that it is well profiled so that the digitisation of your artwork is as accurate as possible to the original's colour, brightness and contrast. To do that you'll want to review our notes on getting the right targets for calibration and note that we recommend using Vuescan scanning software.
Also note that to minimise the amount of spot removal needed (often the most laborious part of art reproduction) we recommend cleaning the glass on your scanner regularly (use a glass friendly micro-fibre cloth and some rubbing alcohol if needed) and pre-dusting your artworks before scanning them (we use canned air).
Once you have your scan file open in Photoshop, right click on the background workspace outside of your image area, click 'select custom color...' and set it to pure white (that's 255,255,255 in RGB numbers). This helps the eye pick up any problems where the paper tone background isn't stripped away perfectly to the edge later on. (Of course you can set this back to something more comfortable later!).
Now select the crop tool, followed by the straighten tool. Click and
drag with this tool to produce your preferred alignment for the image
(typically using the edge of the sheet the illustration is on works
well), then adjust the crop frame to just at or inside the paper edges.
If it's the case that you're not happy with the alignment of the original's illustrated area in relation to the media edge, or the original's media does not actually have squared corners and straight edges, you can still use the straighten tool or just rotate the image until you're happy with the alignment.
Once you've cropped your image, it is then helpful to adjust your canvas size (via 'canvas size...' in the image menu) to the original media size your illustration is on. In this case we'll set it to precisely A2.
Now we need to duplicate our scan into a new layer for non-destructive editing, label the new layer 'sharpen and spot removal' (labeling layers is good practise so you can easily tell later on what each layer in a working document is doing should you ever need to come back to it).
If you haven't already, now would also be a good time to do a 'Save As' and save your file as a working document in a format that supports layers, such as .psd or .tif or (or even .psb if the document is 16-bit and high enough resolution to get over 4gb in file size).
We also always recommend keeping your original raw scan as an unedited file should you ever need to go back to it.
Now go to the 'filter' menu and navigate to 'smart sharpen' (one of the sub-categories in the 'sharpen' sub-menu).
Set you smart sharpening settings to something modest, at most, and use the preview toggle to observe how much effect your adjustments are making. The precise settings required will depend on your scanner output and personal taste, but in general we see far more over-sharpening out there in the world than under-sharpening, so if in doubt dial it back a bit! We typically start at Amount: 100%, Radius: 1 pixel, Reduce Noise: 10%.
Note any changes you make should only be observable when zoomed in to 100% here and if you decide you've over or under done it later on you can always delete this layer and re-duplicate the background layer to start again (though this will also mean re-doing any spot removal).
What we're trying to achieve in this step is the restoration of the very small amount of sharpness lost due to the scanning process - any light that passes through glass (be it the scanner flatbed, a lens etc) - loses sharpness. Here, we're restoring that sharpness, whilst being very careful not to introduce digital sharpening artefacts. With more modest equipment (like the Epson scanners mentioned above), you will probably generally need just a tad more sharpening than you would with raw scans from our scanner here, which is a much higher quality machine optically.
Now with your 'sharpen and spot removal' layer selected, select the 'spot healing brush tool' from the toolbar and make sure it's set to 'normal' mode and 'content aware'. Then zoom into 100% on your artwork, select an appropriate brush size (you can adjust this on the fly using the
']' keys) and scan methodically over the entire illustrated area, clicking to remove any dust spots, blemishes, stray fibres or mistakes you'd rather not have appear in your reproduction.
Note that we're only doing this for the illustrated area - just ignore any spots on the blank page areas for now, as we'll treat those separately in a later step.
Tip: use the navigator window to keep an eye on which parts of the image you're covering.
Now create a new layer above the 'Sharpen and Spot Removal' layer, label it 'White Mask' and fill it with white using 'Fill...' from the edit menu. Then mask out the entire layer by selecting the White Mask Layer, holding down the alt key (on PC) or the option key (on Apple) and clicking the 'add layer mask' button.
Now select the lasso tool and set it to feather 3 or 4 pixels. Adjust the zoom to fit to your window by hitting ctrl+0 (or cmd+0 on Apple) and do as tight a selection of the illustrated area as you can without actually touching it.
Now invert your selection so that all the area on the page bar the illustrated area is actually selected, then fill with white, again using 'Fill...' from the edit menu.
We now have a pure white mask that runs right to the edge of the page around the illustration and obscures any paper tone or unwanted blemishes in the blank space on the page. Doing it this way avoids having to laboriously spot remove on the blank page later and means that you'll never accidentally leave any tone right on the edge of the page, which is easy to miss in Photoshop.
You may also note that in this case I deliberately removed the signature and date left on the artwork by the artist. You can choose either to do this or not depending on your preference. For more on this topic see our article Should I Sign My Digital Prints.
Create a new curves adjustment layer above the 'White Mask' layer and label it Black Point. Then using the black point slider in the properties window, adjust the input to a point that best suits your artwork. To avoid clipping any detail, hold down the alt key while adjusting the slider to see a black and white overlay on your image. Your image (if scanned correctly) should start out completely white and gradually acquire black pixels as you slide to the right. Setting the black point just to the left of the point where you start seeing black pixels ensures that the darkest part of your images are set to actual black (i.e. RGB 0,0,0 or close to) - without clipping any detail in the lighter shadows.
However, depending on the density of your original artwork this might not be an accurate approach. If your artwork is quite light for instance (for instance, it has no actual blacks in it) - arbitrarily setting the darkest point in it to black would then create overly dense results. So you do need to use your judgement here. Your scanner behaviour should be consistent though, so with a bit of practice you should find the right spot to place the black point in most cases.
On the other hand some types of pen work, paints etc. that are dark can have a reflective surface that reflects the scanner light back into the scanner's sensor, resulting in blacks that are too light. In these cases you'll need to adjust your black point further to the right on the histogram.
To get the black point just right (that is so that a print is almost indistinguishable from the original in tone) can take multiple rounds of print tests and is profoundly aided by using colour accurate, calibrated monitors such as those that we retail. Indeed, if there is one area in all of imaging where you really, truly benefit from a high quality monitor, it's art reproduction.
You can of course come back to adjust this layer after continuing onto the following steps.
Now create another curves adjustment layer above the 'Black Point' layer and label it 'White Point'. Once you have that create a black and white adjustment layer above that.
Select the 'White Point' layer again and then select the white point dropper tool in the properties toolbar.
Now with the White Point layer selected and the white point dropper tool active, zoom in to about 300% and click on one of the darker pixels in the blank page area (be sure not to click on a spot that actually has pencil or pen on it or you will start clipping illustrated area).
The idea here is to clip as much of the paper tone as possible without clipping actual illustrated area. Feel free to zoom in and out a few times (undo and re-do as well etc.) to double check you set the white point at the right point (i.e. when the tonality overall looks good, you can't see any paper tone when zoomed out to fit the window AND there isn't illustration highlight detail missing).
It's unlikely you'll get rid of every pixel of paper tone when inspecting zoomed in AND retain nice tone overall in the illustrated area. But because of the White Mask layer, remaining dark pixels of paper should be limited to just around the edges of the illustrated area. We'll move in and clean up these pesky spots in the final step.
It may be worth re-adjusting the black point in your 'Black Point' layer at this stage too now that you are seeing the overall tonality of the retouched image properly.
Your image should be looking just about finished when zoomed out to fit the window. But the final piece of the puzzle is to zoom back in to 100% and work your way around the edge of the artwork (or any paper tone filled gaps between illustrated areas) and manually apply white over the top of blemishes and inconsistencies. This step is particularly critical if you're planning to enlarge your artwork at all for print.
You can do this by going back to your 'White Mask' Layer and painting white using the brush tool into the layer mask where needed. To see clearly where a mask is applied and where not, tap the '\' key to toggle a light red mask preview on and off.
You're now ready to save your artwork for print. We'd recommend keeping this retouching file safe as a working document to come back to in the course of test printing in case you need to make further adjustments before signing off on a final print file (try as we might, it's often the case that things show up in print that we miss on screen).
When you are ready to save your final print file best to flatten your image to one layer and 'Save As' a separate TIFF document.
After following this guide, you will thus end up with 3 files: