> For the complete documentation index, see [llms.txt](https://morningheartgames.gitbook.io/docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://morningheartgames.gitbook.io/docs/asyncautoexposure/tools-and-shipping/performance-guide.md).

# Performance Guide

## Main-Thread Cost

Typical main-thread cost is under `0.1 ms` because brightness analysis uses `AsyncGPUReadback`.

The plugin avoids synchronous GPU readback during normal runtime processing.

The work is split into:

* GPU blit to downsample and convert to luminance
* Async GPU readback of a small grayscale texture
* CPU averaging when the readback is complete
* GPU blit to apply the current exposure multiplier

## Downsample Factor

`downsampleFactor` controls how much the source image is reduced before analysis.

| Factor | 1080p Analysis Size | Pixels Analyzed | Recommended For           |
| -----: | ------------------- | --------------: | ------------------------- |
|    `4` | 480 x 270           |         129,600 | Desktop and high accuracy |
|    `8` | 240 x 135           |          32,400 | Mobile balance            |
|   `16` | 120 x 68            |           8,160 | Low-end devices           |

Brightness is a low-frequency image property, so high analysis resolution is usually unnecessary.

## Readback Frame Skip

`readbackFrameSkip` controls how often brightness is measured.

| Value | Behavior                  |
| ----: | ------------------------- |
|   `0` | Analyze every frame       |
|   `2` | Analyze every third frame |
|   `4` | Analyze every fifth frame |

For most live camera or video content, `2` is a good default.

The exposure value still interpolates every frame, so increasing this value reduces measurement frequency without making the final blit update less often.

## Mobile Starting Point

For mobile builds:

* `downsampleFactor`: `8`
* `readbackFrameSkip`: `4`
* `targetBrightness`: `0.4`
* `maxExposure`: `3.0`

Use Vulkan on Android when possible. OpenGL ES readback behavior is more driver-dependent.

## Static UI Textures

For `AutoExposureRawImage` and `AutoExposureImage` on static content:

* Leave `Continuous Update` disabled.
* Use `ForceUpdate()` after changing settings.
* Avoid processing the same static texture every frame.

For webcam, video, or changing render textures, enable `Continuous Update` or call the core component manually each frame.

## Mask Cost

Masked processing reads back both the downsampled brightness texture and a downsampled mask. Use masks when they improve the exposure target, especially for subject-focused scenes, but avoid them when whole-frame metering already works.

## Preset Guidance

| Scenario                | Suggested Settings                                           |
| ----------------------- | ------------------------------------------------------------ |
| Desktop webcam          | `downsampleFactor = 4`, `readbackFrameSkip = 2`              |
| Mobile webcam           | `downsampleFactor = 8`, `readbackFrameSkip = 4`              |
| Low-end mobile          | `downsampleFactor = 16`, `readbackFrameSkip = 5`             |
| Fast lighting changes   | Lower `readbackFrameSkip`, raise `adjustmentSpeed` carefully |
| Flicker or noisy source | Lower `adjustmentSpeed`, raise `readbackFrameSkip`           |

## WebGL

WebGL uses the synchronous brightness fallback. Increase `downsampleFactor` and `readbackFrameSkip` to reduce the cost on analysis frames.


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