> For the complete documentation index, see [llms.txt](https://docs.timeinpixels.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.timeinpixels.com/nobe-omniscope/scopes/histogram.md). # 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 color 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** | Adjust histogram gain (25%–2000%) | | **Middle-click** or **Double-click** | Reset gain to 100% | ## Frequency Scale The frequency scale changes how pixel-count differences are displayed without changing the signal-level axis: | Mode | Description | | --------------- | ---------------------------------------------------------------------------------------------- | | **Fit** | Fits the complete histogram curve in the plot | | **Auto detail** | Reveals smaller populations while marking off-scale spikes with triangles at the plot boundary | | **Log** | Compresses large differences in pixel counts so low-frequency detail remains visible | Enable **Hold scale** to keep the current frequency reference while comparing shots. Changing the source or histogram mode resets the held reference. Use **Gain** to magnify the resulting curve manually. ## 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](https://565437294-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-MFqn5MuayPgQPMZ9pwf%2F-MG0ZF6QsbE5exszd6wP%2F-MG0ZoD7UW6vtlttuPhW%2FScreenshot%202020-08-31%20at%2000.51.37.jpg?alt=media\&token=d22c3908-8529-423c-bf05-4af92daa94ac) ![Split RGB Histogram](https://565437294-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-MFqn5MuayPgQPMZ9pwf%2F-MG0ZF6QsbE5exszd6wP%2F-MG0_59b5F8wXUDFAFmf%2FScreenshot%202020-08-31%20at%2000.52.28.jpg?alt=media\&token=3be64ade-d25c-41ab-86c2-729006093b61) ![Luma Histogram](https://565437294-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-MFqn5MuayPgQPMZ9pwf%2F-MG0ZF6QsbE5exszd6wP%2F-MG0ZsXUuc-1UzbcmG83%2FScreenshot%202020-08-31%20at%2000.51.41.jpg?alt=media\&token=5dd57709-b626-48c6-b9b9-12cede8bd48f) ![Hue Histogram](https://565437294-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-MFqn5MuayPgQPMZ9pwf%2F-MG0ZF6QsbE5exszd6wP%2F-MG0ZxM5MHCKDpMw1JEr%2FScreenshot%202020-08-31%20at%2000.52.00.jpg?alt=media\&token=6846db2f-e2ce-4dd6-bcdd-6b9e9e219ddb) ![Saturation Histogram](https://565437294-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-MFqn5MuayPgQPMZ9pwf%2F-MG0ZF6QsbE5exszd6wP%2F-MG0_1-yocQCerXv_MFV%2FScreenshot%202020-08-31%20at%2000.52.05.jpg?alt=media\&token=4601303d-836f-4381-92cb-8bfed6ca6e5f) ## Masking Histogram can be used directly to define mask ranges. ![](https://565437294-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-MFqn5MuayPgQPMZ9pwf%2F-MG0ZF6QsbE5exszd6wP%2F-MG0_t3KEwlySu3tnkBt%2FScreenshot%202020-08-31%20at%2000.53.01.jpg?alt=media\&token=9a0cda40-6299-4c9c-8575-36f7d35270bf) | Input | Action | | ---------------- | -------------------------------------------------------------------------------------------------- | | **Alt + hover** | Show precise value/frequency readout under cursor | | **Click + drag** | Select a range and write it to the active mask domain; dragging can continue beyond the plot edges | 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](https://565437294-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-MFqn5MuayPgQPMZ9pwf%2F-MG3ORpZ8_0p-5etnTpu%2F-MG3OjVxD7R2dfVEjxoS%2F03_combined_masking.gif?alt=media\&token=73886991-2b0c-48eb-9540-c0d90cf02a54) ## 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 | | **Frequency scale** | Choose Fit, Auto detail, or Log scaling | | **Hold scale** | Keep the current frequency reference for shot comparison | | **Gain** | Magnify the displayed curve from 25% to 2000% | | **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](https://565437294-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-MFqn5MuayPgQPMZ9pwf%2F-MG0aTz9gR5aTyEQDb6Q%2F-MG0arfTPQh4fgjwtXCQ%2FScreenshot%202020-08-31%20at%2001.01.51.jpg?alt=media\&token=38d7b028-30d8-4924-88fc-0b71658d24db)