Color Correction
This chapter is from the book
This chapter is from the book
This chapter is from the book
Lesson Files
Lessons > Lesson03 folder
Media
beach_cu.iff
beach_ws.iff
flowers.iff
hiker.iff
mountains.iff
sunset.iff
Time
approximately 45 minutes
Goals
Manipulate images with Shake's color correction tools
Concatenate color nodes
Use the Color Picker
Color match shots that have differing colors
Color correction is a generic term for any process that alters the perceived color of an image. The mere mention of the term sends shivers up my spine, because no two people can ever agree on what looks right, including your clients. The perception of color will no doubt be different for every person who looks at your monitor. So, charge by the hour and color correction will be your friend. Fortunately, Shake provides you with a vast array of color manipulation tools with which to drive up your profits.
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Basic Color Correction Tools
Shake's color is typically described in an RGB range between 0 and 1. The Color nodes are generally either mathematical corrections to color (for example, add .5 to the red channel), or the rearranging of specific color channels.
Many of the color-correction nodes can have identical results. For example, Mult and Brightness are the same command, except Brightness affects all three RGB channels at the same time, whereas Mult allows you to adjust each individual channel. Additionally, other functions such as Lookup and ColorX can also duplicate most of the other color nodes. Although ColorX is the most powerful and complicated node in the Color tab, it is also the slowest because it acts on each individual pixel.
Shake's basic color correctors are split up into atomic nodes that can be rearranged in any fashion you wish. The basic nodes are as follows:
Add
The Add function adds to the R, G, B, or A channels. It will also add color to black areas, including those beyond the image frame, in case you move the image later on.
Brightness
This function is simply a multiplier on the RGB channels and is useful for brightening or darkening an image.
ContrastLum
ContrastLum applies a contrast change on the image, with a smooth falloff on both the low and high ends.
Gamma
A gamma correction affects only the midtones while retaining the black and white values of an image. Pixels with a value of 0 or 1 are unaffected. Only nonblack or nonwhite pixels are adjusted.
Mult
This function multiplies the R, G, B, or A channels. Unlike Add, the Mult operator does not add color to black areas.
Lookup
This performs an arbitrary lookup on your image. It is extremely flexible, allowing you to mimic most other color correction nodes. It's also handy for adjusting color values using a curve.
Reorder
The Reorder operator lets you shuffle channels. The argument to this command specifies the new order. A channel can be copied to several different channels.
Using the Color Nodes
It's time to try out a few of the Color nodes.
- Start Shake.
- Select File > Open Script.
- Go to the Lesson03/scripts folder and load the color1.shk script.
This script has a scenic mountain image connected to some basic color correction nodes.
- Double-click on the Add1 node.
You'll see a + next to the Color parameter. This means that extra parameters can be unfolded.
- Click on the + next to the Color parameter.
This reveals a series of radio buttons with another + to the left of them.
- Click on the + next to the R radio button.
When tuning parameters within the color nodes, you can choose several methods:
- Numerically enter values in the RGB text fields.
- Drag the slider next to each text field.
- Click the Color Picker and select a color from the screen or from the color wheel.
- Use the Virtual Color Picker. If you hold the keyboard character R(ed), G(reen), B(lue), H(ue), S(aturation), V(alue), L(uminance), M(agenta), or T(emperature) and drag left and right in the Parameters workspace, you will modify that parameter.
- To gang up the red, green, and blue sliders, hold down V (for Value) and drag left and right.
- Hold down the R key and drag to the right.
This will add to the red channel.
- Once you have added red, hold down the H key and drag left and right.
This shifts the hue of the color. Modifying using this manner modifies only the color that is added, multiplied, and so on. For example, by dragging a color while pressing S (for saturation) it will not decrease the saturation on the image, only the saturation of the color that you are adding to the image.
- Now let's view and edit each of the other Color nodes attached to the mountains node by double-clicking on it. Go ahead and
experiment by adjusting each node's parameters to see how it affects the image.
When you are done working with the color nodes attached to the mountains image, move onto the tree with the sunset image.
- Now double-click on the Reorder1 node attached to the sunset node.
The Reorder function allows you to easily move the channels around.
- To copy the red channel to all three channels, leaving the alpha alone, type rrra in the channels parameter.
All three color channels come from the red channel.
- View each color channel ending with the alpha channel in the Viewer by clicking on the View RGBA Channels button.
- To remove the alpha channel, type rgbn in the Channels parameter.
The alpha channel turns black.
- To copy the luminance into the Matte channel, type rgbl.
The letter l refers to luminance, which is the average luminance of the color channels.
- Press the C key in the Viewer to show the RGB channels.
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These are just the basic color correction tools in Shake; many more are located in the Color tab.