64-bits of Glorious LightAn Introduction to HDRR

CSE3AGR - Paul Taylor 2009

HDRR vs LDRR

• http://upload.wikimedia.org/wikipedia/commons/1/1d/Farcryhdr.jpg

We are going to look at Colour a little differently...

• Red Green Blue• Luminosity• Chromaticity r and b

Luminosity

• http://www.cambridgeincolour.com/tutorials/color-space-conversion.htm

CIELUV and CIEXYZ

• L u v– L is the Luminance– u and v are the Chromaticity

• X Y Z ( also known as tristimulus values)• These are the amounts of each of the primaries needed for an

observer to see the desired colour• Y is the Luminance• Normalised it becomes CIExyzx = X / (X + Y + Z)

y = Y / (X + Y + Z)z = Z / (X + Y + Z) = 1 - (x + y)

An XYZ graph

Why are we going to do this?

• http://en.wikipedia.org/wiki/YCbCr

RGB and sRGB

• RGB is Gamma independant Range [0,1]• sRGB utilises a Gamma of 2.2 and a D65

Whitepoint

Colour Format Factors

Lab Gamut Efficiency- % of visible colours represented

Coding Efficiency- % of data space that represents real colours (waste)

The Lab Gamut

RGB Colour Spaces• http://www.brucelindbloom.com/index.html?

WorkingSpaceInfo.html#Specifications

 

Adobe RGB

sRGB

NTSC RGB

PAL / SECAM RGB

sRGB to XYZ

http://www.brucelindbloom.com/index.html?Eqn_RGB_XYZ_Matrix.html#WSMatrices

sRGB->XYZ XYZ->sRGB

XYZ to Luv D65 = Xr=95.04, Yr=100.00, Zr=108.88

http://www.brucelindbloom.com/index.html?Eqn_RGB_XYZ_Matrix.html#WSMatrices

Luminance

• http://colorusage.arc.nasa.gov/lum_and_chrom.php

Light of an equal power, but different wavelength does not appear equally bright to the viewing eye.

Chromaticity

• Chromaticity r and g from a CIE RGB source:

http://en.wikipedia.org/wiki/CIE_1931_color_space#Definition_of_the_CIE_XYZ_color_space

U’ and v’

• http://www.nikon.com/about/feelnikon/light/chap03/sec01.htm

Why are we doing this?

• http://en.wikipedia.org/wiki/YCbCr

HDRR vs LDRR

• http://upload.wikimedia.org/wikipedia/commons/1/1d/Farcryhdr.jpg

HDRR vs LDRR

• http://upload.wikimedia.org/wikipedia/commons/1/1d/Farcryhdr.jpg

Y Cb Cr (YCC)

• What is it?– A Colour Format yes– Y is the luma– Chroma Blue– Chroma Red

• Y’CbCr has a non-linear luma (Gamma encoded)

• http://en.wikipedia.org/wiki/YCbCr

CIE Chromacity Diagram

• http://en.wikipedia.org/wiki/File:CIExy1931.svg

Using all this to create HDRR

Emulating Light

• Our Contrast adaption is an adjustment of the iris, a relatively slow chemical change

• Dynamic Contrast of the eye is 1,000,000 : 1• Static Contrast of the sys is 10,000 : 1

Light Blooming

• When Light scatters in the Lens of your Eye• The brain interprets this as a bright spot.

– This has the effect of really bright stuff bleeding over the edges of other objects.

• Emulating this bleeding makes the player think the white spot is insanely bright!

Lens Flare

• This is the diffraction of light in the lens of your eye

• It results in rays of light emanating from small light sources, and possible chromatic effects.

• We have been emulating this effect for a long time, but with HDRR can also include the bleeding / distortion in relating to world objects

Screen Effects (Not all HDRR)

• Depth blur (Near and Far)• Motion Blur• Full Screen Bloom• Material Bloom• Cross fading (Cinematic)• Screen Distortions (Various)

– Heat Haze– Colour Filters (Night Vision)

• HDRR effects!!

Tone Mapping

• This is us trying to jam 1,000,000 : 1 contrast ratio onto a screen which may have only 5,000 : 1 ratio.

• Luv / XYZ benefits• Light Mixing• Two lights A and B• All possible outputs lie

directly between the two points

LogLuv Encoding

• LogLuv is a great format for punching down the size of LUV encoded data into variables such as Int8’s or similar smaller data sizes

HDR Teapot

References

• http://www.xnainfo.com/content.php?content=28

• http://www.absoluteastronomy.com/topics/Full_screen_effect

• http://www.absoluteastronomy.com/topics/High_dynamic_range_rendering