Wednesday, 9 September 2015

Color Sharpening-- focus on CAN3

Sean Michael Robinson:

Greetings folks.

Last week I received a message from John Funk that his last printing session for CAN3, focusing on the numbered bonus prints, had gone off without a hitch. He also sent along this nice message, with some praise for the new printing facilities, and some feedback on the prepress/print prep--

I just had to tell you how great the black and the colours against the black on BP-23 looks! WOW is all I can say. I showed it to the print company staff and even compared it to a proof I had with me from May (their previous machine). NO comparison. This one has deep, deep, very rich black and the colours just jump off the page against the rich black. It looks stunning. You must have done some more fine tuning on this one (and other as well probably) because I don’t recall the last proof I sent you looking as good as todays production printing did! I just hope Dave has a silver pen to sign them with.
With that in mind, I thought I'd give you all a technically oriented walk-through of prepping that image for print. If you're bored by tech talk, this is a good place to tune out :)

 Here's a view of the raw scan, scanned on Dave's Epson WF7510, which has reasonably good color balance and sharp enough optics at this resolution, especially considering the price. 

As Dave had specifically requested that this image be treated as a "finished" image rather than a "warts and all" color reproduction a la the porfolios, there are several different things for me to do here. First, let's take a look at the image at 50 percent zoom. (When working on sharpening levels etc you should always be viewing the image at 100 or 200 percent, but with the dimensions of images required for the blog, you'd be seeing basically no information. :))

Raw scan, at 50 percent.

So as I said before, it's a reasonable scan. The image looks a bit dull color-wise, and it's soft, in need of some sharpening. The black is also washed-out. Since the black border is such a major feature of the image, and will serve to anchor every other color adjustment we do, let's adjust that first--

In Photoshop CC, Cntrl-L will bring up the Levels command-

The little black arrow on the far left represents the black point, the point where the software will recognize absolute black (in this case, 100 percent of Cyan, Magenta, Yellow, and Black). In a photograph, this type of adjustment ("crushing the blacks") would be verboten for many styles of photography, as you're losing any information to the left of the point. Or more specifically, you're crushing that information into a more uniform black. 

In this case, because a lot of the color modeling was worked pretty dark, I can't move the black point very far without changing the color cast as well. So I end up moving it a bit to the right, then moving the mid point (the grey arrow in the middle) to the left a bit, until all I've done is blackened the blacks and not affected the rest of the color. Here's what that looks like.

Raw scan plus "Levels" adjustment

Okay, now let's address some of the softness in the scan.

Before we do any kind of sharpening at all, you first need to confirm that your scan is already the right size of your destination. In other words, if you'll need to scale your image at all, it's best to do this before you do any sharpening. This is because any scaling inevitably softens the image, which might require more sharpening afterwards.

(The book Real World Image Sharpening by the late great Bruce Fraser actually recommends sharpening on output, at least in the case of photographs that might need to be printed at varying sizes, on varying media, for different purposes. This workflow might also make sense for you. In my case, I'm saving each of these steps as a layer, so it's easy to back out if something else comes up in the future that requires something radically different.)

First off--what's sharpening, and why do we need it?

I'm going to quote myself from the last time I wrote about color sharpening--

For a wide range of reasons, and to varying degrees, all digital imaging techniques invariably soften an image. This is true whether you're working with a digital camera, or a flatbed scanner, or even a high-end drum scanner. Additionally, all methods of full-color reproduction do the same thing. Picture, if you will, the millions of tiny colored dots that make up the average full-color print. Through a miraculous flaw in your vision, the result appears as a continuous tonal image. But the result of all those dots is a diffusion of detail, a "softness" that's difficult to avoid. 
So, you improve your output device, you improve your substrate, i.e. your paper. Coated paper holds ink with less expansion, therefore, your dots can be smaller, carrying more detail from source to print. Additionally, you compensate for what expansion there is with correction curves that try to predict dot gain and adjust accordingly. But still, the image gets softer.
That's where sharpening comes in. 
Sharpening is essentially contrast-boosting edges, controlled by threshold (i.e. what is considered an edge), amount (strength), and radius. The radius is what gives you real control. How large of an area should this effect cover? Smaller radii bring out high-frequency detail, and larger radii are for softer-focus targets.

Okay, we're going to do two passes of sharpening here. The first one will be high-frequency--addressing itself to the small details, namely the grittiness of some of the paint and the small lines. I bring up the Unsharp Mask tool--

The Threshold is essentially "what gets seen as an edge?" The lower the Threshold, the more of the image is affected. I've set a very low Threshold here to affect more of the image-- I want to bring out some of the very small texture of the paint and paper first. I've also set a low radius-- the radius is the size of the effect that's generated. Larger radiuses can look like halos-- smaller ones are much more subtle. Lastly, I've kept the amount down fairly low, so that the overall effect is fairly mild.

Here's the result.

Everything looks just a bit more textured, and the very small white on black sections are now really popping.

Okay, now I'm going to address the colors again. They look a bit dull compared to the other scan of this image I've seen. So I'm going to use the Saturation control and up the saturation of the colors just a bit.

Then I go ahead and apply one more pass of sharpening, this time with a higher Threshold (affecting less of the image) and a higher radius (wider sharpening effect overall).

Here's the result--

Lastly, I use the "Select from Color Range" tool to select only the black, and make that pure black. Next I extend the black border a little further to make this a full-bleed print.

 After printing out the image, I notice the Cerebus logo could probably use some color flattening as well. So I use the same trick-- "Select From Color Range" grabs the logo, which I then fill with a single color, eye-droppered from the logo itself.

And here's a screenshot of the final product. (Click to enlarge)

Of course, the real destination is always the print itself--

1 comment:

Scott Yoshinaga said...

I hope you will one day put all of your scanning and other techniques into an ebook. Very valuable information for those of us who do print work with scanned art!

Thanks for all of the updates!