HDR Sample

Category: Visuals

Min PC GPU: Fermi -based (GTX 4xx)

Min Tegra Device: Tegra 4

Description

This sample demonstrates High Dynamic Rendering with Auto-Exposure and Tonemapping

APIs Used

GL_COMPUTE_SHADER
glDispatchCompute
glMemoryBarrier
glGenFramebuffers
glBindFramebuffer

Shared User Interface

The OpenGL samples all share a common app framework and certain user interface elements, centered around the "Tweakbar" panel on the left side of the screen, which lets you interactively control certain variables in each sample.

To show and hide the Tweakbar, simply click or touch the triangular button positioned in the top-left of the view.

Other controls are listed below:

Device	Input	Result
touch	1-Finger Drag	Orbit-rotate the camera
	2-Finger Drag	Move up/down/left/right
	2-Finger Pinch	Scale the view
mouse	Left-Button Drag	Orbit-rotate the camera
	Right-Button Drag	Move up/down/left/right
	Middle-Click Drag	Scale the view (up:out, down:in)
keyboard	Escape	Quit the application
	Tab	Toggle Tweakbar visibility
gamepad	Start	Toggle Tweakbar visibility
	Right Thumbstick	Orbit-rotate the camera
	Left Thumbstick	Move forward/backward. Slide left/right
	Left/Right Triggers	Move up/down

Technical Details

Introduction

High Dynamic Range (HDR) imaging has become an essential feature for both photography and game graphics.

Dynamic range is simply defined as the ratio in brightness between the brightest and darkest parts of an image. HDR images allow the full range of brightness in a scene to be captured accurately.

For a full description see: http://en.wikipedia.org/wiki/High-dynamic-range_imaging

Rendering Procedure

Render Scene to an RGBA16F FBO at full dynamic range.
Downsize (filter) scene buffer by 4x in both dimensions for post processing.
Downsize (filter) the result by a further 16x in each dimension. Run a compute shader on the result to generate a single luminance value for auto-exposure calculations.
Extract the highlighted areas for further processing by thresholding luminance values above and below an adjustable cutoff. Scale the result as desired.
Generate a pyramid of processed images, computing another Gaussian blur on each.
Generate highlight streaks in four directions.
Generate ghosted highlight images in 2 passes.
Composite the passes into a final image.
Compress the result to low dynamic range via tonemapping and gamma correction to the onscreen RGB888 framebuffer.

UI

Enable/Disable draw background
Enable/Disable auto exposure
Exposure key adjustment
Select scene
Select material
Select model
Select glare type

References

ftp://download.nvidia.com/developer/presentations/2004/6800_Leagues/6800_Leagues_HDR.pdf

http://en.wikipedia.org/wiki/High-dynamic-range_imaging

http://www.daionet.gr.jp/~masa/

http://http.developer.nvidia.com/GPUGems2/gpugems2_chapter20.html