False Color Shader

False Color shader for Godot 4 that visualizes scene luminance as color-coded exposure levels.

This shader samples the final screen image, calculates accurate luminance using perceptual weights, and remaps brightness values to distinct colors. It helps identify overexposed areas, clipping, crushed shadows, and midtone balance instantly.

Useful for:

• Lighting and exposure debugging

• Preventing blown highlights and lost shadow detail

• Achieving consistent visuals across different displays

Designed as a fullscreen CanvasItem shader, easy to toggle during runtime.

No guesswork — see actual brightness values instead of relying on your monitor.

How to use

Add this script to ColorRect Node:

extends ColorRect

func _ready():
    visible = false

func _input(event):
    if event is InputEventKey and event.pressed and event.keycode == KEY_X:
        visible = !visible

Steps:

1. Create overlay

• Add ColorRect node

• Set anchors to full screen (Layout → Full Rect)

2. Assign shader

• Create ShaderMaterial

• Paste shader code

• Assign material to ColorRect

3. Run scene

• You will see false color overlay

4. Toggle on/off (optional)

• Attach script to ColorRect

• Use your key (e.g. X) to show/hide

How to read it:

#FFFFFF (white) — fully blown out
#FFCCCC (light red)
#FF0000 (red) — clipping
#FF8000 (orange)
#FFCC00 (yellow-orange)
#FFFF00 (yellow) — bright
#CCFF00 (yellow-green)
#80FF00 (lime)
#33FF33 (light green)
#00FF00 (green) — lower midtones
#4D4D4D (gray) — mid range
#33CCCC (light cyan)
#00CCFF (cyan)
#0080FF (light blue)
#0033FF (blue)
#0000FF (deep blue) — shadows
#4D00CC (violet)
#800099 (purple)
#33004D (dark purple)
#0D001A (near black) — crushed shadows

How to use it:

• Turn it ON

• Look for:

  • too much red/white → reduce light

  • too much blue/purple → increase light

• Aim for balanced distribution (some gray, controlled highlights)

• Turn it OFF and check final look

Shader code

shader_type canvas_item;

uniform sampler2D screen_texture : hint_screen_texture;

void fragment() {
    vec3 rgb = texture(screen_texture, SCREEN_UV).rgb;
    float lum = dot(rgb, vec3(0.2126, 0.7152, 0.0722));

    vec3 c;

    if (lum > 0.95)      c = vec3(1.0);                // white
    else if (lum > 0.90) c = vec3(1.0, 0.8, 0.8);      // light red
    else if (lum > 0.85) c = vec3(1.0, 0.0, 0.0);      // red
    else if (lum > 0.80) c = vec3(1.0, 0.5, 0.0);      // orange
    else if (lum > 0.75) c = vec3(1.0, 0.8, 0.0);      // yellow-orange
    else if (lum > 0.70) c = vec3(1.0, 1.0, 0.0);      // yellow
    else if (lum > 0.65) c = vec3(0.8, 1.0, 0.0);      // yellow-green
    else if (lum > 0.60) c = vec3(0.5, 1.0, 0.0);      // lime
    else if (lum > 0.55) c = vec3(0.2, 1.0, 0.2);      // green light
    else if (lum > 0.50) c = vec3(0.0, 1.0, 0.0);      // green
    else if (lum > 0.45) c = vec3(0.3);                // mid gray
    else if (lum > 0.40) c = vec3(0.2, 0.8, 0.8);      // cyan light
    else if (lum > 0.35) c = vec3(0.0, 0.8, 1.0);      // cyan
    else if (lum > 0.30) c = vec3(0.0, 0.5, 1.0);      // blue light
    else if (lum > 0.25) c = vec3(0.0, 0.2, 1.0);      // blue
    else if (lum > 0.20) c = vec3(0.0, 0.0, 1.0);      // deep blue
    else if (lum > 0.15) c = vec3(0.3, 0.0, 0.8);      // violet
    else if (lum > 0.10) c = vec3(0.5, 0.0, 0.6);      // purple
    else if (lum > 0.05) c = vec3(0.2, 0.0, 0.3);      // dark purple
    else                 c = vec3(0.05, 0.0, 0.1);     // near black

    COLOR = vec4(c, 1.0);
}

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