Tuesday, September 29, 2015

Optimizing a Scan, Part 1: Levels

In this post I’m going to cover my process for tweaking a color scan of an illustration. I’ll be making my editing decisions based on the file’s Histogram and by my monitor. In order to “trust” the image on my monitor, I make sure to keep it calibrated. I use the Spyder Pro for my monitor calibration, but there are other good systems out there.

My scanner is the Epson Expression 10000XL, which I highly recommend. It’s easy to use, captures lots of detail, and can scan up to 12 by 17 inches.

I start off by selecting “Professional Mode” with “No Color Corrections” (please see Figure A). I want to make all my adjustments in Photoshop—I don’t want the scanning software to make any of the decisions for me.

Figure A: The Epson interface.

I open up the scan in Photoshop and compare it to the original, which I prop up on an easel right next to my monitor as I tweak the file. I know from experience that my scanner tends to scan a little too light and the colors a little too flat. The first thing I do is open up a Levels Adjustment Layer (see screenshot B below), which is the non-destructive and more flexible alternative to using a Levels adjustment (cmd-L) directly on the pixel Layer.

B: Levels Adjustment Layer at the bottom of the Layers Panel.

As a side note, I tend to use Levels for scanned artwork and Curves for photographs. Curves will give you more control over the tonal adjustment because you can add points, but I’ve found that Levels is generally fine for scans.

When you open up a Levels Adjustment Layer, you’ll see the Histogram under the Properties Panel. The Histogram plots on a graph all the pixels in the image based on their tonal value (see screenshot C below). The illustration in this example shows a dark figure against a fairly large, light background. I used black ink for the line, so I want to make sure that the lines are dark black.

C: You can see the gap in the shadow area of the
original scan and the adjustment made by sliding the Black Point
over to close the gap. You can also see that most of the pixels
on the graph fall toward the lighter side, which is what
you'd expect with this image. 

When I look at the Histogram, I see that there’s a gap between the actual pixels in the scan and the Black Point (or darkest black), which is normal for my scanner. That ensures that I don’t lose detail in the darkest areas of my scan. I also see that my highlight areas extend all the way to the lightest tone, so I won’t need to adjust my highlights for this scan. I also notice that most of the pixels fall toward the highlights, which I’d expect with an image that has so much light background in it.

To correct for the shadows, I slide the Black Point (or Shadow) to the place where the pixels in the Histogram start (see C above). Whenever I make an adjustment, I always click on and off the Eyeball (to show and hide) for the Layer Adjustment to evaluate the change.

By moving the Black Point over to make up for the gap in the Histogram, I am making sure that my image will contain the full tonal range and not look washed-out (see D below). This will also make the colors a little more saturated.

D: Before Levels adjustment on the left, and after on the right.
Notice that the red is richer after the adjustment. Click to enlarge.

Next up: Optimizing a Scan, Part 2: Adjusting Color Balance and Hue/Saturation (to come).

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