# Histogram

The Histogram scope shows value distribution across the selected signal domain. Use it for exposure distribution, channel clipping checks, and mask-range selection.

## Modes

| Mode           | Description                                                                                                                                                                                                                                   |
| -------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| **RGB**        | Combined R'G'B' code-value histogram — counts across all three channels overlaid                                                                                                                                                              |
| **Split RGB**  | Separate R/G/B histograms (available only in **RGB + Horizontal** layout)                                                                                                                                                                     |
| **Luma**       | Luma (Y') distribution — weighted sum of the non-linear R'G'B' channels using the active colour space's luma coefficients (Rec. 709: 0.2126 / 0.7152 / 0.0722; Rec. 2020: 0.2627 / 0.6780 / 0.0593). Not to be confused with scene luminance. |
| **Hue**        | Hue distribution across 0–360°                                                                                                                                                                                                                |
| **Saturation** | Saturation distribution (0–100%)                                                                                                                                                                                                              |

## Layout & Zoom

| Setting                              | Description                           |
| ------------------------------------ | ------------------------------------- |
| **Horizontal / Vertical**            | Histogram orientation                 |
| **Left to right**                    | Direction control for vertical layout |
| **Mouse wheel**                      | Vertical zoom/scaling (25%–2000%)     |
| **Middle-click** or **Double-click** | Reset zoom to 100%                    |

## Scale & HDR Guides

Histogram scale follows the active project/input scale (IRE, %, 8-bit, 10-bit, PQ, HLG). Non-linear scales like PQ and HLG are **absolute** — their bins correspond to decoded nit values via the inverse EOTF, so a peak in the 1 000 nit bin means *1 000 nits*, regardless of the display the scope is running on.

When HDR scale mode is set to **HDR Reference**, PQ/HLG guides include key labels such as:

* **26 nits** — SDR-equivalent midtone reference
* **203 nits** — SMPTE ST 2084-A reference diffuse white
* **1 000 nits** — most common HDR mastering-display peak

Legal-range guides (narrow-range / video-range code values from Rec. 709 and Rec. 2020) are shown where applicable:

* **8-bit video legal**: 16 / 235
* **10-bit video legal**: 64 / 940

![RGB Histogram](/files/-MG0ZoD7UW6vtlttuPhW)

![Split RGB Histogram](/files/-MG0_59b5F8wXUDFAFmf)

![Luma Histogram](/files/-MG0ZsXUuc-1UzbcmG83)

![Hue Histogram](/files/-MG0ZxM5MHCKDpMw1JEr)

![Saturation Histogram](/files/-MG0_1-yocQCerXv_MFV)

## Masking

Histogram can be used directly to define mask ranges.

![](/files/-MG0_t3KEwlySu3tnkBt)

| Input            | Action                                              |
| ---------------- | --------------------------------------------------- |
| **Alt + hover**  | Show precise value/frequency readout under cursor   |
| **Click + drag** | Select range and write it to the active mask domain |

Mask target by mode:

* **RGB / Luma**: luma range mask
* **Hue**: hue mask
* **Saturation**: saturation mask

Combine this with shape masks from [Source Signal](/nobe-omniscope/scopes/source-signal.md) for full qualifier workflows.

![Combined masking](/files/-MG3OjVxD7R2dfVEjxoS)

## Appearance

| Setting                   | Description                            |
| ------------------------- | -------------------------------------- |
| **Fill Opacity**          | Fill intensity from none to 100%       |
| **Render histogram edge** | Outline the histogram curve            |
| **Show gradient**         | Draw color gradient in the background  |
| **Adaptive scaling**      | Auto-fit visible range for readability |
| **Smooth Graph**          | Smooth curve rendering                 |

## Custom Reference Lines

Up to four custom reference lines are supported.

Per line:

* Enable/disable line
* Set value in current scale
* Set line color

These are useful for recurring deliverable limits or internal targets.

## Example Views

![Vertical histogram orientation](/files/-MG0arfTPQh4fgjwtXCQ)


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