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Cleaning Tutorial 02 – Levels

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In the last tutorial we prepared a page for cleaning. In this tutorial you’ll learn how to properly level  a page.

This tutorial isn’t meant to be a comprehensive explanation on how to level every type of image quality you’ll see. That would take a long time to write and it would never be complete. This is meant to explain what the tools needed can do and show a basic example. I will write separate tutorials for more difficult page types later.

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Levels

Let’s start with the simpler of the two. Levels. I’ll explain the Levels window and show how to clean a really simple page. This is the Levels Window:

levels_window

From top to bottom/left to right here are the features:

  1. Presets can be made if you notice you are using the same value changes for many pages.
  2. Channels are used to select the color channel you wish to edit (Value, Red, Green, Blue, or Alpha). Unless working with a color image it should always be set to Value.
  3. Linear and Logarithmic Histogram. It changes how the Input Levels histogram is rendered. I’ve found little use for it.
  4. Histogram. It displayes how the particular channel’s values are spread across the spectrum. Left is darker and right is lighter
  5. Input Sliders. You can click and drag these to shift the balance of the values. Pulling the black slider right makes the darks darker and pulling the white slider right makes the lights lighter. the ‘Gamma’ slider in the center alters the mid-tones. Left for lighter and right for darker.
  6. Droppers and boxes are another method of changing the input value. Selecting the black dropper and then clicking a spot on the image that should be black, the balance will shift so that all pixels of that shade and darker will be black. Vice-versa for the white dropper. The black and white boxes accept inputs between 0 and 255. The middle Gamma box accepts decimal inputs between 0.10 and 10 with 1 being the middle.
  7. The output levels slider is basically a brightness/contrast slider. It has minimal use if a leveled image look too bright or whatever. The boxes accept input between 0 and 255
  8. The Auto button levels the page automatically. It can be good for estimates and sometimes does great, but never trust it to do all of the work. It’s not perfect. The droppers are identical to the ones beneath the histogram with the inclusion on a gray dropper which is virtually useless since manga achieves it’s midtones primarily through patterns and line density.
  9. Edit these settings as curves takes all of the settings you’ve set and opens them in the curves window. This can be used to create a base template for a cuves preset or something but I’ve yet to actually do so.
  10. The preview tick decides whether yhe things you do in the levels window are rendered in real time on the image as a preview. This should always be ticked.

Now for an example. Here’s the page we’ll be using:

Levels_SampleIf you look at the image iat it’s full size it’s easy to see that there’s what looks like a film overlaying the blacks (it’s most prominent in the bottom left corner). We should get rid of that because it’s absolutely bugging me.

Note: If you can’t see the film of dirt on the blacks then you’re monitor is full of fail and you’ll either need to replace it or do some srs setting changes before I’d ever hire you as a cleaner.

Open up the Levels window (No default shortcut). Try fiddling with a few options on your own and seeing what you can come up with, and then read below.

If you tried the Auto button like I know you did, you’ll see that it severely underleveled the page. It hardly changed at all. With a page like this an easy way to get a good figure is to select the black dropper and then click around a few spots. You should get some figures between 30 and 50. In this case we don’t have to worry about overleveling much so let’s go with 50 to be sure.

01_01

Looks like the page is done, yeah? Well you’d probably be able to get away with it in most groups but we’re going the extra mile because we can.

Hit cancel in the levels window and then open up the Threshold window by going Color>Threshold. Let me get this straight. Never use this for anything except what I’m about to tell you. It’s a horrendous tool that uglifies anything it’s used on.

Open it up and move the black slider to around 245-248 by pulling it or entering a number in the box. See those speckles around some of the lines? You might not have been able to see them before but they’re there and depending on some computers’ graphic settings the user will see them too.

01_02

Alternatively you can use a sharpening filter with a strength of around 85-89. It works better but is more cumbersome. Just go Filters>Enhance>Sharpen and set the slider before hitting ok. Make sure to undo the filter before continuing. There are other ways to check for the dirt but they depend on your computer’s display options. If you have a setting called something like “image sharpening” then you should be set.

01_03

So close the threshold window, reopen the Levels window and set the black value back to 50. Next input somewhere around 248-250 for the whites. Whites don’t need to change as much as the blacks did. Most of the dirt should be gone now if you recheck.

You might have noticed the grays got darker when you input the value for the blacks. It shouldn’t be a significant difference and leaving it be might make the page look better but let’s fuck with it so I can show you how the gamma slider works.

The gamma slider’s counter works backwards from the other ones. As it moves left the value in the box goes up instead of down. So to make the grays lighter you need to increase the value. you can try clicking and dragging a bit until you get it right. See if you can get the grays the same shade they were at before we started leveling the page. You can compare by ticking and unticking the preview box. To get the grays close to the original shade the gray slider needs to be at around 1.25. You should also raise the black value to around 60 or so since some dirt will form when you alter the gray level.

01_05

So now we’ve got the levels window set properly and it’s time to accept the changes. Hit ok and the changes will be set to the layer you are working on.

Closing Notes:

The page might still have some dirt on it, mostly in the bottom right corner, but leveling any harder might compromise the rest of the image so that needs to be done by hand.

If you were clicking buttons and pulling sliders but nothing was happening then make sure that you have the middle layer selected. The top layer is transparent and so nothing you do will change it and the bottom layer is covered by the middle layer and any changes won’t be seen unless you reorder them or toggle the middle layer’s visibility.

I know this tutorial is long and probably explains a lot of stuff that a monkey can figure out but hang with it. After a while you’ll be leveling pages like this in seconds. It’s also one of the most important steps in cleaning so getting all of the information down is essential.

Bad leveling irks me more than bad redraws just because it’s not hard nor particularly time consuming but people still neglect to do it right.

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Download Files

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Written by PIR

January 16, 2009 at 14:03

Posted in Tutorials

Tagged with , , ,

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