Levels

Remaps input and output brightness ranges with gamma correction, per-channel or on the master. Includes a live histogram display.

Category: Color Menu path: Color > Levels

Ports

Port	Type	Direction	Description
in	imageRgba16f	input	Input image
out	imageRgba16f	output	Adjusted result

Parameters

The Levels node has a channel selector and 5 controls per channel (Master + Red + Green + Blue = 20 scalar params total).

Param	Type	Default	Description
channel	enum	Master	Which channel set to display in Properties. Options: Master, Red, Green, Blue.

Master Channel

Param	Type	Default	Description
inBlack	scalar	0.0	Input black point. Values at or below this become output black.
inWhite	scalar	1.0	Input white point. Values at or above this become output white.
gamma	scalar	1.0	Midtone gamma. Values < 1 darken midtones, > 1 brighten them.
outBlack	scalar	0.0	Output black point. Remapped minimum brightness.
outWhite	scalar	1.0	Output white point. Remapped maximum brightness.

Per-Channel (Red, Green, Blue)

Each channel has the same 5 controls, prefixed by the channel name:

Param	Type	Default	Description
redInBlack / greenInBlack / blueInBlack	scalar	0.0	Per-channel input black point
redInWhite / greenInWhite / blueInWhite	scalar	1.0	Per-channel input white point
redGamma / greenGamma / blueGamma	scalar	1.0	Per-channel midtone gamma
redOutBlack / greenOutBlack / blueOutBlack	scalar	0.0	Per-channel output black point
redOutWhite / greenOutWhite / blueOutWhite	scalar	1.0	Per-channel output white point

All parameters are keyframeable.

How It Works

The GPU shader processes each pixel through two stages. First, the master levels remap the overall brightness: input values are clamped to [inBlack, inWhite], normalized to [0, 1], gamma-corrected, then scaled to [outBlack, outWhite]. Then per-channel levels apply the same process independently to R, G, and B.

The processing order is: unpremultiply alpha, apply master levels, apply per-channel levels, repremultiply alpha.

Histogram

The Properties panel shows a live histogram of the input image. The histogram is computed from a blitted-down version of the input texture and displays R, G, B, and Luminance distributions on a log scale. The histogram is cached and only recomputed when the input changes (not during playback, for performance).

Usage Examples

Basic: Increase contrast

1. Add a Levels node after your image source
2. Set inBlack to 0.1 and inWhite to 0.9
3. This crushes the shadows and highlights, increasing overall contrast

Creative: Color tinting via per-channel levels

1. Switch to the Red channel and raise outBlack to 0.1
2. This adds a red tint to the shadows
3. Switch to Blue and lower outWhite to 0.8 for warm shadows with cool highlights

Advanced: Animated exposure correction

Keyframe gamma from 0.5 to 1.5 to animate a brightness shift over time. Unlike exposure (which is a linear multiply), gamma reshapes the midtones while preserving blacks and whites.

Tips

• Use the histogram to identify clipped highlights or crushed shadows before adjusting
• The gamma slider is the most useful single control -- it adjusts brightness without affecting the extremes
• inBlack > inWhite inverts the tonal range (negative effect)
• Per-channel adjustments are applied after master, so they refine the overall adjustment
• All 20 params are keyframeable, enabling animated color grading

Related Nodes

• Curves -- more flexible per-channel tone control with arbitrary curves
• ColorCorrect -- CDL-style grading (exposure, saturation, temperature)
• Invert -- full channel inversion