Wednesday, 29 October 2014

Scannerpalooza


Sean Michael Robinson:

Greetings!

Many thanks to everyone who contributed to the amazing Kickstarter campaign. It's because of your generosity and interest that we're able to move this project forward.

And so, forward it goes! 

Ever since I've come on board, Dave and I have been discussing on and off how to accomplish the bulk of the scanning to be done. It's a big problem -- a 4,000 pages of original artwork kind of problem, putting aside the photo negatives for a minute. Which, Dave suggested, makes it really a matter of speed. What is the fastest acceptable way to generate the raw material?

I spent a lot of time on this research. Digital cameras or medium-format cameras with digital backs? Not enough resolution, or too expensive. Upscaling? Feasible, with the right scans. Auto Document Feeds? Not with precious artwork, on illustration board, with tone.

But even when I resigned myself to the old standby, the flatbed scanner, the speed concern helped us narrow the field, basically to two possibilities. Seeing as one of those possibilities cost about three times as much as the other, it made sense to get some sample scans from the cheaper of the two.

The Plustek OpticBook 300 is an A3 sized CCD scanner. With a 10 second scan time at 600 ppi, it's ideal in speed, if nothing else. Now to get an image sample...

I called up a Plustek sales rep, who was very helpful in sending me a sample scan. And what, you might ask, can approximate fine line art material on aging art board? 

How about a dollar bill?


Here's the sample scan. 



So, the Washington scan is a very good stress-test for a line art scanner, because not only is there a ton of very fine line information, it's "hiding" within the color information, making potential problems like color aberration or misalignment of color channels more apparent than if you were straight scanning black line art on pure white board.

So, let's see how it handles under manipulation.

First off, we're going to upscale our information, doubling the size of the image (and doubling the potential size of our bitmap output). You can see from the close-up below that this 600 ppi scan hasn't really grabbed all of the line art information that was present-- not surprising when you think of the lengths the U.S. Treasury goes to keep their bills from being counterfeit. So by upscaling, we're hoping to wring a little bit more information from the scan.

I go to Image -> Image Size, and double the resolution. Select "Preserve Details" as your method. This is a new addition to Photoshop CC, and it's a huge improvement over the previous enlargement algorithym, "Bicubic Smoother," which tended to soften edges as you upscaled. 

Here's a close-up of a segment, before and after.




Now we're going to flip through the color channels to find the cleanest channel. The red channel has some noise in it (visible above), what looks to be paper damage, and the blue channel has a lot more paper noise overall. So green channel it is.


So I toss the other channels and convert the mode to grayscale, and then duplicate the layer, so that I can flip back and forth between the adjusted version and un-adjusted version, as need be.

Next I make a levels adjustment to "knock out" the remaining gray of the paper as much as possible, while also raising the black point to the position where the blacks actually appear on the histogram.


The result is still very, very soft. If this was a series of images, I'd take some time now to develop the best possible sharpening routine for the material, and write this whole thing into an executable script, that I can run any time I want to. But since this is just for you and me, I'll do this the "brute force" way. I use Unsharp Mask, at 500 percent, with the radius set to a very fine 1.2 pixels, since the information I'm trying to retain is very fine detail information.

That's still not enough, so I level-adjust one more time, getting rid of the white "sharpening halos" by bringing the white point down a bit, and then run Unsharp Mask one more time, with the same settings, at about 200 percent. And here's the result!

Conclusion? For our purposes, this scanner will work great.

It's worth mentioning that I used the dollar bill as a target both because it's ubiquitous (the gentleman I spoke to would be likely to have one in his pocket), but also because of its difficulty. This is several degrees harder task than scanning hand-drawn black lines on white art board. That being said, if I was looking for a scanner specifically for the purpose of scanning extremely fine information, like the bill, or, say, Victorian-era copperplate engraving or mezzotint printing on coated stock, I'd be tempted to go with a scanner with more optical sharpness to start with. But, once again, for our purposes, the Plustek should be perfect.

7 comments:

Jeff Seiler said...

Sean?

You're a genius!

David Birdsong said...

A counterfeit genius. N'yuk. N'yuk.

Michael said...

I don't understand why upscaling is even being talked about. You can't upscale without introducing artifacts. Period. Please take the extra time to scan at a higher resolution.

Michael

Sean R said...

Hey Michael,

If you can wait till next week, I'll give a thorough upscaling demonstration then. Trust me when I say I've tested a dozen variations, and I'm a very picky. I'd agree with you if we were talking about anything other than line art-- but scanning in color, upscaling, and then outputting at bitmap, it makes no difference, as long as certain conditions are met.

Bicubic smoother, which I was using before, does indeed have some issues, specifically, it doesn't work if the scanning stage had sharpening applied, or if you enlarge too much, and additional softness is introduced into the scan. But Preserve Details is really something, at least, for this particular application.

(For those who don't know, every doubling of resolution quadruples your scan time, hence talking about these issues. There's the additional hurdle of many scanner's "higher res" settings being so optically soft that you might as well have upscaled in the first place.)

Sean R said...

Also, as I mentioned in the post, if I were scanning source material with this fine of information, I wouldn't be scanning at 600 ppi. This is only for oversized original art scans, not for at sized materials. (Photo negs, print scans etc are being scanned at 1200 ppi)

Travis Pelkie said...

I believe the Comics Code was put into place precisely to stop demonstrations of crimes like this. Apparently we're now part of a counterfeiting ring due to reading Cerebus.

;)

I don't know enough of the technical stuff to be able to comment in depth, but it's cool to have these posts available for people. Maybe some more B&W '80s indies can learn from this.

Sean R said...

Hey Travis--

"Your dollars at work!"

"Stretching your donations... past the breaking point."