Color Correction in NUKE Foundry Colour
Learn Color Correction in NUKE to work with Color Correction nodes like Color GRADE, Color GAMMA, Color ADD, Color MULTIPLY, Color EXPOSURE and Color-Look-Up node for NUKE Color Correction.
This ‘Nuke Color Correction’ tutorial explains how to use Nuke’s Color Correction nodes to adjust the appearance of the images in your composites.
Actually, the Color Correction required in nearly every plate of your composites. The question is why? Because, (1) if we shoot a scene either in indoor or outdoor doesn’t matter, should require some color correction for final presentation. And (2) if we render a 3D scene either in 3ds Max or Maya, should require some color Correction also for final presentation. We all know that every two shoot is different with different light and color values when we shoot with real life camera.
At the time of real life shooting, the main concentration of the camera-man goes to the angle to frame a subject and how it looks through the lens. Here, the camera man has very little time to think about the color information of other plates already stored.
In case of rendered output form 3D scenes the matter is the same. Here CG artists have to concentrate on many technical things at the time of rendering. He/she has very little time to think about the color information.
And we all know that one good color corrected scene can attract lots of audience. If the same scene is edited with wrong color information then audience will reject its viewing. For this reason, good color correction is always in high demand. And you will agree with me that Foundry Nuke is the software developed basically for that purpose.
In this ‘Nuke Color Correction’ tutorial we will learn how to use different nodes and their properties to color correct an image. Here, I have to give you some information about color values. We all know that we can’t see anything without light and every image is the result of reflected lights form objects. That is why at first you have to learn to find the darkest pixels and brightest pixels of an image. The black point and white point is the two key poles/points for color correcting a scene. The color range from black point to white point which is called the Gamma value is also a very important subject in this matter.
In this ‘Nuke Color Correction’ tutorial you’ll learn about the use of few color-correction nodes and their properties.
- Multiply node for ‘Nuke Color Correction’
With the use of ‘Multiply’ node basically you can modify the white points of the image pixels. The incoming bright pixels will be effect most while the dark pixels very much stay locked. So using the multiplication isn’t going to contaminate the black pixels too much. If you increase the multiply value then the bright pixels get more bright and the overall result is brighter image. But if you decrease the multiply value then the bright pixels get darker and the overall result is darker image like the following.
You can find the Multiply node from Color > Math > Multiply from the tool node list. Also you can pick color using the color picker (arrow marked) then Ctrl+click on any point of the image to multiply the value with the picked color from the clicked point. In addition you can use color slider (arrow marked) to choose color for multiplication.
- Exposure node for ‘Nuke Color Correction’
This node has the same effect as the Multiply node. In addition it has four Adjust-in options like Stops, Light, Densities and Cineon (by default the Densities option is selected). When the gang option is checked then if you move the slider to increase the value of all three channels (red, green, blue) the bright points will be brighter and the image get bright. The opposite will be happen when you decrease the value of all three channels at the same time. Dark points will not get effect much with this modification.
This is the output example of increasing and decreasing values.
In this node you can work on all color-channels as well as red, green and blue channel individually. You can work on single color channel or two as your requirement by using two different techniques.
The first one -
Just deselect the non-required color channel/channels check box and move the color channel slider with gang option checked on. Here only red value is decreased because green and blue channel field is not selected.
The second one -
Uncheck the gang check box and move the color channel sliders as your requirement. Here red channel is decreased and blur channel is increased separately.
- Add node for ‘Nuke Color Correction’
Add or plus also often called offset. It simply adds a constant value to the entire image, no matter the pixels are dark or bright. If you increase the value then every pixels gets brighter gradually without considering the black point or white point. Actually, it lifts the image to bright with constant pressure on every corner of the image.
If you want to work with an image containing an alpha channel then Add node can create problem. Here ‘Add’ node convert total image without respecting the alpha information. But, here you have one handy solution comes with the ‘Add’ node itself and that is the ‘(un)premult by’ or the un-pre-multiply value. To limit the effect comes from the ‘Add’ node, just select rgba.alpha from the drop-down list of the ‘(un)premult’ value. The following is the example.
- Gamma node for ‘Nuke Color Correction’
Gamma nodes modify the color values of the mid-tones of the image while maintaining the black point and white point. The Gamma node acts on the mid-tones connect like a rubber band. It keeps 0 and 1 in place. While brightening or darkening the mid-tones values. The resulting effect is like the following.
You can also use color slider window to modify the Gamma values with your desired color. Here also you can notice that the bright point and dark point still the same after modification.
- ColorLookUp node for ‘Nuke Color Correction’
ColorLookUp node helps you to modify color using color curves. You can use ColorLookUp node to adjust contrast, gamma, gain and offset values with many other operation. Color curves refer to line graphs of a given color channel’s brightness value. The horizontal axis of the color curves represents the channel’s original, or input, values, and the vertical axis represents the channel’s new, or output values.
Here, you can work only on master curve or can choice any color-channel like red, green, blue, alpha. The point at 0 is the black point and 1 is the white point of the image. To insert any point on the curve click on the curve while holding down the Ctrl and Alt (keyboard shortcuts) key from the keyboard. Then move the point with the left mouse button and you can see the resulting effect in the viewer panel. To delete a point from the curve just select the point and press delete button from the keyboard.
The following image shows the resulting effect on the image after modifying the master curve.
It is important to understand here is that everything beyond 0 and 1 is destructive. And if the curve gets instant height gain after the white point then it is nothing but a destructive editing. It can be happen when you add a point on a curve and push it downward then the resulting curve gets the erect shape at or after the white point. Always you should have to maintain the shape of the curve at or after the white point. How? Simple, add a point just after the white point with soft-hand for every channel then start editing.
The following is the effect after modifying every color-channel.
- Grade node for ‘Nuke Color Correction’
In Grade node we have more control to color correct the image. Let’s start from the top properties.
blackpoint - If we modify the black-point value then actually we are remapping the black-point value of the respective dark pixels with the incoming value. That means now the incoming value will be considered as 0. For example, if the new incoming value is 0.02 for the black-point then calculation will start from 0.02 for other properties. Note that black point means the darkest pixels of the image considered as the black point.
Whitepoint - With white point value modification, we are actually remapping the value of the white point of the respective bright pixels with the incoming value. Now the incoming value will be considered as 1. For example if the new incoming value is 1.5 for the white-point then calculation will start form 1.5 for other properties of this grade node. Note that white point means the brightest pixels of the image considered as the white point. If you increase its value then bright pixels will get fade.
Lift - Lift is related with the black-point value. It can just lift the dark pixels to white. If you increase the lift value then dark pixels will get brighter in respect of the black-point value. It simply creates the reverse effect with the black-point increment. For example, if the black-point value is set to 0.1 and the new lift value is also 0.1 then you can get back the original image.
Gain - Gain is related with the white-point value. It can just input gain to color pixels basically the bright pixels. If you increase the gain value then bright pixels will get more brightness in respect of the white-point value. It simply creates the reverse effect with the white-point increment. For example, if the white point value is set to 1.5 and the new gain value is also 1.5 then you can get back the original image.
Multiply - It has the ability to multiply the color values of the image pixels.
Offset - Offset property works from black to white. By default its value is 0. You can go through the range of -1 (complete black) to +1 (complete white).
Gamma - As you know the Gamma value works between white point and black point values. If you increase its value then intermediate pixels values between black point and white point will turn to white gradually. The opposite will be happen when you decrease its value.
I think the Grade node is the most intuitive one to learn the color information of an image. All these nodes are used for correcting the color in Nuke. I think this Nuke Color Correction tutorial will help you.