> ## Documentation Index
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# ImageSDRToHDR - ComfyUI Built-in Node Documentation

> The Convert SDR to HDR node expands standard dynamic range sRGB images into Rec.2020 HLG HDR.

The **Convert SDR to HDR** node expands standard dynamic range sRGB images into Rec.2020 HLG HDR. It keeps the existing look of the image and maps its brightness into a wider range, so the result must be saved with an HDR color space selected. Alpha is preserved unchanged.

## Inputs

| Parameter | Description | Data Type | Required | Range |
| - | - | - | - | - |
| `image` | The SDR image(s) in sRGB to expand into HDR. | IMAGE | Yes | - |
| `algorithm` | HDR expansion algorithm. Selecting an algorithm reveals its parameters (`target_luminance`). | DYNAMIC\_COMBO | Yes | `"lottes"` |

### lottes Inputs

These parameters appear when `algorithm` is set to `"lottes"`.

| Parameter | Description | Data Type | Required | Range |
| - | - | - | - | - |
| `target_luminance` | Peak-white target in nits. 0 keeps the calibrated rendering. Dark images are not normalized to this peak. (default: 650.0) | FLOAT | Yes | 0.0 to 10000.0 (step 1.0) |

Each image of the batch is converted separately: the sRGB encoding is inverted to linear light, the brightness is expanded with a Lottes-style rational curve blended with a calibrated monotonic log-gain curve, and the result is re-encoded as Rec.2020 HLG. Because the output is HDR, the save node must use the `HDR` color space; saving it as sRGB renders the brightness incorrectly.

HLG assumes a 1000-nit reference display, so `target_luminance` values below 1000 keep that reference and a value of `0` leaves the calibrated rendering untouched. Single-channel images are expanded to three channels before conversion, and the alpha channel is copied through unchanged.

## Outputs

| Output Name | Description | Data Type |
| - | - | - |
| `IMAGE` | The Rec.2020 HLG HDR image(s). | IMAGE |

> This documentation was AI-generated. If you find any errors or have suggestions for improvement, please feel free to contribute! [Edit on GitHub](https://github.com/Comfy-Org/embedded-docs/blob/main/comfyui_embedded_docs/docs/ImageSDRToHDR/en.md)

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