Tips & Tricks
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Page last updated on
February 14th, 2009
This article was originally written for The ASFA Quarterly,
the newsletter of The Association of Science Fiction Artists.
I have adapted it slightly for this site.
Let's suppose, for the sake of argument that you have:
a) access to a computer that has a copy of Adobe Photoshop,
one of the most widely used image-processing tools available
b) a flatbed scanner hooked up to that computer
c) a desire to get some images onto the computer.
If none of these apply to you then this article probably won't either. Feel free to skip forward to some other section. If the above describes you adequately then you're in the right place. I'm going to try to explain in basic terms a bit about scanning images.
Some may be wondering why you would want any of your art on the computer. There are a number of good reasons. Perhaps you want to show it off on your web page or e-mail someone a sample of your work. You can use the computer to archive your photo-reference files. I've found it very handy to use my computer to fax editors rough sketches for illustrations using my computer. I also combine my sketches in Photoshop to get a final layout for an illustration, and then use that to produce color roughs which I can put up on the web for an Art Director to peruse. So as you see, there are many possible reasons for wanting to scan things in. So now let's look at how we do that.
There's a lot more to good scanning than just placing an image on the flatbed scanner, pressing "scan" and then saving the file. The first thing that we should look at is how the scanner works. If you've ever watched a scanner do its thing, you might have noticed that it looks a lot like a copying machine in action. The part of the scanner that is moving across the picture and projecting all of the light actually holds thousands of little image-samplers. You've got many of these things crammed into an inch: If you're using a scanner capable of scanning 600-dpi (dots per inch) then you've got 600 mini-scanners lined up in each inch, each one sampling 1/600th of your image when they're all in operation. The number of dots per inch is called the resolution.
When you're scanning, it's always a good idea to scan at a resolution that divides into your scanner's resolution easily. Huh? What did I just say? Let's use the example of that 600-dpi scanner and I'll go over it better. If you scan at 600-dpi then all of the little scanning heads are activated and each does his job. But we can scan in at a lower resolution than the scanner's maximum capability. What happens if I decide to scan at 300-dpi? 300 goes evenly into 600 twice, so when scanning, every other sampling head will be active. If I scan at 200-dpi, every third one will be sampling when I scan. Scanning at 75-dpi activates every 8th scanning head. What happens when I choose to scan at some arbitrary number like 72-dpi? That number doesn't go into 600 evenly, so I sometimes get every 8th scan head, sometimes every 9th. It varies and it's not an even spread. As a result, my scan is not going to be as even as if I had scanned the same image at, say, 150-dpi and then resized the image to be 72-dpi.
So that brings up the question "What-dpi should I scan at?" That all depends on what you're scanning in an image for. If you're using an image as a computer desktop background, it only needs to be the size of your screen. That number will vary from monitor to monitor, but as an example, an iMac's monitor (and many other computers' too) is 800 pixels across by 600 pixels down at 72-dpi. (See, that 72 I pulled out of a hat above wasn't completely arbitrary! That's a standard resolution for computer monitors.) If you're putting something on the web, you have to decide how large you want it: remember, larger also means "takes longer to download." You might want smaller images of your work so that something else can fit on the screen, such as some text or more images. So now you're talking about a few hundred pixels on a side.
What if you're scanning something for eventual use in printing, such as for a book cover? Your resolution needs to be twice the line screen that your printer is using. Most book covers that I've worked on have been printed on a 150 line screen press, so the final files that they've needed from me have been at 300-dpi. Anything more than that is unnecessary. However, I will often work larger than that to allow me to put more detail into the a picture. It's the same way you wouldn't think of supplying a 4 by 7 inch final painting for a paperback book cover: You're usually going to be working larger than that.
So let's look at some specific techniques for scanning different kinds of images. We'll start with a simple greyscale image such as a pencil sketch. Place the image on the scanner and use whatever scanning software your scanner came with. (Sorry I can't be more specific, but every scanner will use something different.) This is usually found in the File/Import menu in Photoshop. Use the "Preview" command to get a quick thumbnail image of how your picture looks on the scanner. Use the selection tool to choose just the area that you want to scan. After all, why scan more than you need to? Make sure that you scan your pencil sketch in "Greyscale" mode. Scanning in color (or "RGB" as your scanner controls may say) is just going to take three times longer to give you information that you don't need. You can also set what dpi you're scanning at. You generally want to scan in these images pretty high-resolution. I'm going to scan in mine at 300-dpi.
In this image, you can see my scan. The paper came out a bit dark and the contrast is low. We'll use "Levels" tool to fix that problem. (Command-L on a Mac, Control-L on a PC.) You will end up using this tool on just about everything you scan so here's how it works...
In figure 2 you'll see a histogram of my image. That's a diagram that shows the range of all the grays in your image from pure black on the left to white on the right. As you can see, we have no blacks or whites in our image: The areas on the far left (black) and far right(white) are empty. Most of the values are in the middle-right area which signifies a light gray. By moving the triangles at the bottom towards the center, we can spread out our range of grays more.
See where the histogram peaks on the right? That's the shade-of-gray that we have the most of in the image. In this case, it's the color of the paper, which is reading as a light gray. The white triangle on the right shows where our absolute white value is. It started on the far right. When I move it to the left I'm taking those plentiful light-grays and turning them into the white-most value. By moving the black triangle to the left, I'm taking the darkest values in the image and pushing them more towards black. You can see the results of these adjustments in figure 3:
The background is now a pure white and the dark parts are blacker. Those areas are still not 100% black, but if I'd wanted them to be, I'd have moved the black triangle further to the right.
If we wanted to scan in a color photograph that we had taken, we'd set the scanner to "color" or "RGB." (RGB stands for Red Green Blue. That's the way a computer monitor or a television keep track of color.) We can scan this in at any resolution. If you want it as detailed photo-reference, you may want it high resolution, such as 300dpi. You may only want it to put up on a web page, in which case you could use 150dpi or lower. Scanning the photo will take a bit longer than a black and white image because the scanner has to do three passes, one for Red, one for Green, and one for Blue. The file size will also be larger because three times the amount of information most be stored. Once the image is scanned, you can use the Levels tool to adjust the dark and light areas in the same way that you did with the earlier images.
If you're scanning in an image from a magazine, there are some additional steps that you'll need to take. That's because a magazine has been printed with a screen, and your scan will pick up all of the individual dots that were screened. Often you will get a moiré pattern which will make the dot patterns look worse. This scan at 200dpi shows an example of this problem.
The solution is to scan in much more information than we need and then blur it together a bit to get rid of the obvious screen patterns. Scan the image in at a much higher resolution that you actually need. I'll try mine at 600dpi, but it would be fine to go even higher. Zoom in and out of the picture until you get a view which shows the dot pattern clearly. (To Zoom, use Command-plus and -minus on a Mac, Control-plus and -minus on a PC.) Now we use the Gaussian Blur to blur our ugly moiré dots together. Make sure that the "preview" checkbox in the Blur tool is checked so that you can see how the values affect your image. Start with a setting of 1 pixel and then go up or down from there. I usually end up with a value somewhere between .8 and 1.4.
When you blur the image, you'll be losing some of its crispness to get rid of the moiré. Once the pattern is gone, we can bring back a bit of the sharpness by using the Unsharp Mask tool (In the Filter / Sharpen menu.) Don't let the name fool you, this tool will sharpen your image, not unsharpen! Set Threshold to 0 and Radius to 1.0, and then fool around with the Amount to see what looks good. Start at 100% and tweak it from there. Be careful not to sharpen it too much because your picture will get little halos where the black areas hit the light ones. Once you're done, you can shrink the image down to a more convenient size in order to save file space. When I shrink it down to 200dpi after having done the above corrections, it looks a lot better than my first try. This last image shows the new, improved version.
I have one last tip about scanners. Don't limit yourself to only scanning in flat images. Cloth and found objects are great things to bring into the computer to use for imaging. I have more than once scanned in a pair of blue jeans to incorporate the denim texture into a picture. I have placed pencils, flower petals, and watch gears on my scanner (covering them with a white cloth instead of the scanner lid) to import unique images. Feel free to experiment, and above all, have fun!