Visualize HDR Sample

Category: Visuals

Min PC GPU: GeForce Kepler-class

Min Tegra Device: Tegra K1

@ GitHub: Visualize HDR Sample Source Code

Description

The Visualize HDR sample acts as a viewer for HDR images.

APIs Used

OpenGL ES 3 AEP

Shared User Interface

The Graphics 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
	A	Show TweakBar, Toggle Focused Item
	B	Close Focused UI, Hide TweakBar
	DPAD Up/Down	Move Focus to Prev/Next Item
	DPAD Left/Right	Decrease/Increase Focused Item

Technical Details

This sample is an implementation of the Weighted Blended OIT (Order Independent Transparency) algorithm from this research paper:
McGuire and Bavoil, Weighted Blended Order-Independent Transparency, Journal of Computer Graphics Techniques (JCGT), vol. 2, no. 2, 122--141, 2013.

Introduction

The Radiance format (.HDR/.RGBE) is a popular format used for storing HDR images. This application is specially designed to work with HDR displays as displays images saved in the Radiance format. When connected to a compatible display, options show up in the application UI that allow tweaking of various settings of the ACES tonemapper and visualize their effect on the image.

All images used in this sample are courtesy of Epic Games Inc.

Rendering Procedure

A typical HDR image has values that go from 0.0 to well beyond 1.0. Typically images of this form are tonemapped to fit between the 0 to 1 range so that they work well with backbuffers that are RGB888. In our case, we use the ACES tonemapper to tonemap our image to an alternate range which has far more precision and range than the previous 0-1 range. The ACES tonemapper also takes into account the color space that the original image is stored in (scene-referred) and also the final output color gamut capabilities of the display. If the display is capable of higher peak brightness levels, the tonemapper curve can tone the final output based on that as well. The ACES tonemapper could be run completely as a final pass in the fragment shader, but in this case, it is implemented as a LUT. The 32x32x32 FP16 LUT stores the entire range of input to output color mappings for quick access from the fragment shader. This significantly reduces performance overhead.

UI

Image Chooser
Output Curve (based on max display brightness)
Output Color Space
Output Mode (final image passed to the driver)
Enable ACES D60 to D65 White Adjustment
Enable ACES desaturation
Enable ACES Dim Surround
Adjustment of Middle Gray
Tone Curve Saturation
Surround Gamma
Max CLL
Splitscreen mode