Презентация Practical implementation of sh lighting and hdr rendering full-length онлайн

Содержание слайда: Practical Implementation of SH Lighting and HDR Rendering on PlayStation 2 Yoshiharu Gotanda 　 Tatsuya Shoji Research and Development Dept. tri-Ace Inc.

Содержание слайда: This slide includes practical examples about SH Lighting for the current hardware (PlayStation 2) HDR Rendering Plug-ins for 3ds max

Содержание слайда: SH Lighting gives you… Real-time Global Illumination

Содержание слайда: SH Lighting gives you… Soft shadow (but not accurate)

Содержание слайда: SH Lighting gives you… Translucent Materials

Содержание слайда: HDR Rendering gives you… Photo-realistic Light Effect

Содержание слайда: HDR Rendering gives you… Photo-realistic Sunlight Effect

Содержание слайда: HDR Rendering gives you… Photo-realistic Depth of Field Effect adds depth to images

Содержание слайда: SH and HDR give you… Using both techniques shows the synergistic effect

Содержание слайда: Where to use SH and HDR Don’t have to use all of them SH lighting could be used to represent various light phenomena HDR Rendering could be used to represent various optimal phenomena as well There are a lot of elements (backgrounds, characters, effects) in a game It is important to let artists express themselves easily with limited resources for each element

Содержание слайда: Engine we’ve integrated Lighting specification (for each object) 4 vertex directional lights (including pseudo point light, spot light) 3 vertex point lights 2 vertex spot lights 1 ambient light (or hemi-sphere light) Light usage is automatically determined by the engine

Содержание слайда: Engine we’ve integrated Lighting Shaders Color Rate Shader (light with intensity only) Lambert Shader Phong Shader

Содержание слайда: Engine we’ve integrated Custom Shaders (up to 4 shaders you can choose for each polygon) Physique Shaders (Skinning Shader) Decompression Shaders Static Phong Shader Fur Shaders Reflection Shaders (Sphere, Dual-Paraboloid and so on) Bump Map Shader Screen Shader Fresnel Shader UV Shift Shader Projection Shader Static Bump Map Shader

Содержание слайда: Rendering Pipeline Our engine has the following rendering pipeline

Содержание слайда: Rendering Pipeline

Содержание слайда: Where have we integrated? HDR : Adapting data for HDR -> Modifying mesh data Applying HDR effects -> Post effect SH Lighting : Precomputing -> Plug-in for 3ds max Computing SH coefficients of lights -> CPU SH Shading -> Lighting Shaders

Содержание слайда: High Dynamic Range Rendering

Содержание слайда: Representing Intense Light Color (255,255,255) as maximum value can't represent dazzle How about by a real camera?

Содержание слайда: Optical Lens Phenomena By camera - Various phenomena caused by light reflection, diffraction, and scattering in lens and barrel These phenomena are called Glare Effects

Содержание слайда: Glare Effects Visible only when intense light enters May occur at any time but are usually invisible when indirect from light sources because of faintness

Содержание слайда: Depth of Field One of the optical phenomena but not a Glare Effect DOF generally is used for cinematic pictures

Содержание слайда: Representing Intense Light - Bottom Line Accurate reproduction of Glare Effects creates realistic intense light representations Glare Effects reproduction requires highly intense brightness level But the frame buffer ranges only up to 255 Keep higher level on a separate buffer (HDR buffer)

Содержание слайда: What is HDR? Stands for High Dynamic Range Dynamic Range is the ratio between smallest and largest signal values In simple terms, HDR means a greater range of value So HDR Buffers can represent a wide range of intensity

Содержание слайда: Physical Quantity for HDR For example, when you want to handle sunlight and blue sky at the same time accurately, int32 or fp32 are necessary at least

Содержание слайда: Implementation of HDR Buffer on PS2 PS2 has no high precision frame buffer - Have to utilize the 8bit-integer frame buffer Adopt a fixed-point-like method to raise maximum level of intensity instead of lowering resolution (When usual usage is described as “0:0:8", describe it as “0:1:7" or “0:2:6" in this method) Example: If representing regular white by 128, 255 can represent double intensity level of white Therefore, this method is not true HDR

Содержание слайда: Mach-Band Issue Resolution of the visible domain gets worse and Mach-Band is emphasized But with texture mapping, double rate will be feasible

Содержание слайда: Mach-Band Issue

Содержание слайда: Mach-Band Issue – with Texture

Содержание слайда: Tone Mapping One of the processes in HDR Rendering It involves remapping the HDR buffer to the visible domain

Содержание слайда: Tone Mapping Typical Tone Mapping curves are nonlinear functions

Содержание слайда: Tone Mapping on PS2 But PS2 doesn't have a pixel shader, so simple scaling and hardware color clamping is used

Содержание слайда: Tone Mapping on PS2 PS2's alpha blending can scale up about six times on 1 pass dst = Cs*As + Cs Cs = FrameBuffer*2.0 As = 2.0 In practice, you will have a precision problem, so use the appropriate alpha operation:0-1x, 1-2x, 2-4x, 4-6x for highest precision

Содержание слайда: Tone Mapping - Multiple Bands Multiple bands process to represent nonlinear curves

Содержание слайда: Tone Mapping - Multiple Bands But in cases of more than two bands, it is necessary to save the frame buffer and accumulate outcomes of scaling; rendering costs will be much higher We don’t use Multiple Bands

Содержание слайда: Glare Filters on PS2 Rendering costs (Typical) Bloom 5-16Hsync Star (4-way) 7-13Hsync Persistence 1Hsync (frame buffer size : 640x448)

Содержание слайда: Basic Topics for Glare Filters use Reduced Frame Buffer Filtering Threshold Shared Reduced Accumulation Buffer

Содержание слайда: Reduced Frame Buffer Using 128x128 Reduced Frame Buffer All processes substitute this for the original frame buffer The most important tip is to reduce to half repeatedly with bilinear filtering to make the pixels contain average values of the original pixels It will improve aliasing when a camera or objects are in motion

Содержание слайда: Filtering Threshold In practice, the filtering portion of buffer that are over threshold values The threshold method causes color bias that actual glare effects don't have

Содержание слайда: Filtering Threshold This method could be an approximation of a logarithmic curve for Tone Mapping ??

Содержание слайда: Shared Reduced ACC Buffer Main frame buffers take a large area so fill costs are expensive Use the Shared Reduced Accumulation Buffer to streamline the main frame buffer once

Содержание слайда: Work Buffer List Buffer sizes depend on PSMCT32 Page unit Buffer sizes will be 128x96 or 128x72, an aspect ratio of 4:3 or 16:9, considering maximum allocation

Содержание слайда: Bloom Using Gaussian Blur (Detail later) The work buffer size is 128x128 - 64x64

Содержание слайда: Bloom - Multiple Gaussian Filters Use Multiple Gaussian Filters MGF can reduce a blur radius compared with single Gaussian. Specifically, it helps reduce rendering costs and modifies filter characteristics

Содержание слайда: Bloom - Multiple Gaussian Filters Use 3 Gaussian filters in our case Radii are: 1st:40%, 2nd:20%, 3rd:10% of single Gaussian

Содержание слайда: Star Create each stroke on the work buffer and then accumulate it on the ACC Buffer Use a non-square work buffer that is reduced in the stroke's direction to save taps of stroke creation Vary buffer height in order to fix the tap count

Содержание слайда: Star Issue Can't draw sharp edges on Reduced ACC buffer Copying directly from a work buffer to the main frame buffer can improve quality But fill costs will increase

Содержание слайда: Persistence Send outcomes of filtering to Persistence Buffer as well as ACC Buffer Persistence Buffer size is 64x32 A little persistence sometimes improves aliasing in motion

Содержание слайда: More Details for Glare Filters Multiple Gaussian Filters How to create star strokes and so on.. See references below Masaki Kawase. "Frame Buffer Postprocessing Effects in DOUBLE-S.T.E.A.L (Wreckless)“ GDC 2003. Masaki Kawase. "Practical Implementation of High Dynamic Range Rendering“ GDC 2004.

Содержание слайда: Gaussian Blur for PS2 Gaussian Blur is possible on PS2 It creates beautiful blurs Good match with Bilinear filtering and Reduced Frame Buffer

Содержание слайда: Gaussian Blur Use Normal Alpha Blending Requires many taps, so processing on Reduced Work Buffer is recommended Costs are proportional to blur radii Various uses: Bloom, Depth of Field, Soft Shadow, and so on

Содержание слайда: Gaussian Filter on PS2 Compute Normal blending coefficients to distribute the pixel color to nearby pixels according to Gaussian Distribution Don’t use Additive Alpha Blending

Содержание слайда: Gaussian Filter on PS2 Example: To distribute 25% to both sides 　1st pass, blend 25% / (100%-25%)=33% to one side 　2nd pass, blend 25% to the other side

Содержание слайда: Gaussian Filter on PS2 Gaussian Distribution can separate to X and Y axis This way, you can blur an area of 3x3 (the radius of 1 pixel) with only 4 taps of up, down, left and right Otherwise, blurring the area takes 9 taps

Содержание слайда: Gaussian Filter on PS2 In addition, using bilinear filtering you can blur 2 pixels once That is … 5x5 area with 4 taps 7x7 area with 8 taps 15x15 area with 28 taps …

Содержание слайда: Lack of Buffer Precision 8-bit integer does not have enough precision to blur a wide radius. it can blur only about 30 pixels Precision in the process of calculations is preserved when using Normal Blending, but it's not preserved when using Additive Blending

Содержание слайда: Gaussian Filter Optimization Of course using VU1 saves CPU Avoiding Destination Page Break Penalty of a frame buffer is effective for those filters In addition, avoiding Source Page Break Penalty reduces rendering costs by 40%

Содержание слайда: Depth of Field Achievements of our system: Reasonable rendering costs: 8-24Hsync(typically), 35Hsync (frame buffer size : 640x448) Extreme blurs Accurate blur radii and handling by real camera parameters Focal length and F-stop

Содержание слайда: Depth of Field

Содержание слайда: Depth of Field overview Basically, blend a frame image and a blurred image based on alpha coefficients computed from Z values Use Gaussian Filter for blurring Use reduced work buffers : 128x128 – 64x64

Содержание слайда: Multiple Blurred Layers There are at most 3 layers as the background and 2 layers as the foreground in our case We use Blend and Blur Masks to improve some artifacts

Содержание слайда: Hopping Issue with Layers But hopping tends to occur when using more than two layers We usually use 1 BG and 1 FG layers or 1BG and 2FG layers

Содержание слайда: Formula for Blur Radius The optical formula for DOF below is acquired from The Thin Lens Formula and the formulas for camera structure relativity x: diameter of blur in projector (circle of confusion) o: object distance p: plane in focus f: focal length F: F-stop

Содержание слайда: Conversions of Frame Buffers DOF uses the conversions of frame buffers below (details later) Swizzling Each Color Element from G to A or A to G Converting Z to RGB with CLUT Shifting Z bits toward upper side

Содержание слайда: Pixel-Bleeding Artifacts With wider blurs, Pixel-Bleeding Artifacts were fatally emphasized

Содержание слайда: Pixel-Bleeding Artifacts Solve it by blurring with a mask Use normal alpha blending so put masks in alpha components of a source buffer Gaussian Distribution is incorrect near the borders of the mask but looks OK

Содержание слайда: Edge on Blurred Foreground Generally, blurred objects in the foreground have sharp edges Need to expand Blending Alpha Mask for the foreground layers

Содержание слайда: Edge on Blurred Foreground But using the reduced Z buffer leaves the masks a little blurred To expand or not is up to you

Содержание слайда: Expand Mask Our way also blurs and scales Blending Alpha Mask but intermediate values are broken Maybe there are better ways of expanding Blending Alpha Mask

Содержание слайда: Unexpected Soft Focus Appears among layers or between a layer and the midground, or appears a little blurred Emphasized when a blur is wide

Содержание слайда: Unexpected Soft Focus One solution is to increase the number of layers Another way is to put intermediate values on the blurring mask But it causes incorrect Gaussian blurring areas

Содержание слайда: Intermediate Mask of Gaussian

Содержание слайда: Intermediate Mask of Gaussian

Содержание слайда: Intermediate Mask of Gaussian

Содержание слайда: Unnatural Blur Gaussian Function is different from a real camera blur The real blur function is more flat Maybe the difference will be conspicuous using HDR values

Содержание слайда: Z Testing when Blending Layers Advantage Clearer edge with a reduced Z buffer

Содержание слайда: Z Testing when Blending Layers Disadvantage Hopping results when objects cross the borders of layers

Содержание слайда: Converting Flow Overview DOF flow

Содержание слайда: Converting Flow Overview Glare Effects flow

Содержание слайда: Swizzling Each Color Element from G to A or A to G Look up a PSMCT32 page as a PSMCT16 page

Содержание слайда: Swizzling Each Color Element from G to A or A to G Copy with FBMSK

Содержание слайда: Converting Z to RGB with CLUT Convert PSMZ24 to PSMCT32

Содержание слайда: Converting Z to RGB with CLUT Look up as PSMT8

Содержание слайда: Converting Z to RGB with CLUT Requires many tiny sprites such as 8x2 or 4x2, so it's inefficient if creating on VU When converting a larger area, using Tile Base Processing for sharing a packet is recommended

Содержание слайда: Issue of Converting Z to RGB Use CLUT to convert Z to RGB, so it can take only upper 8-bit from Z bits Upper Z bits tend not to contain enough depth because of bias of a Z-buffer Solve by shifting bits of the Z-buffer to upper BETTER WAY is setting more suitable Near Plane or Far Plane

Содержание слайда: Shifting Z bits toward Upper Side Step1 Save G of the Z-buffer in alpha plane Step2 Add B the same number of times as shift bits to itself for biasing B Step3 Put saved G into lower B with alpha blending (protect upper B by FBMASK of FRAME register)

Содержание слайда: Outdoor Light Scattering

Содержание слайда: Outdoor Light Scattering Implementation of: Naty Hoffman, Arcot J Preetham. "Rendering Outdoor Light Scattering in Real Time“ GDC 2002. Glare Effects and DOF work good enough on Reduced Frame Buffer, but OLS requires higher resolution, so OLS tends to need more pixel-fill costs Takes 13-39Hsync (typically), 57Hsync

Содержание слайда: Outdoor Light Scattering Adopting Tile Base Processing High OLS fillrate causes a bottleneck, so computing colors and making primitives are processed by VU1 during previous tile rendering

Содержание слайда: Additional Parameters 2nd Mie Coefficients Can represent more complex coloring No change to fill costs

Содержание слайда: Additional Parameters Gamma It’s fake. It isn’t correct physically But it would be most useful

Содержание слайда: Additional Parameters Horizontal Slope & Gain Use the function from “Perez all weather luminance model” with a modification

Содержание слайда: Additional Parameters Z bit Shift Is more important than using it with DOF

Содержание слайда: OLS - Episode Shifting Z bits causes a side effect where objects in the foreground tend to be colored by clamping values Artists found and started shifting Z bits as color correction, so we provided inexpensive emulation of coloring

Содержание слайда: Spherical Harmonics Lighting

Содержание слайда: How to use SH Lighting easily? Use DirectX9c! Of course, we know you want to implement it yourselves But SH Lighting implementation on DirectX9c is useful to understand it You should look over its documentation and samples

Содержание слайда: Reason to use SH Lighting on PS2 Photo-realistic lighting

Содержание слайда: Reason to use SH Lighting on PS2 Dynamic light

Содержание слайда: Reason to use SH Lighting on PS2 Subsurface scattering

Содержание слайда: PRT Precomputed Radiance Transfer was published by Peter Pike Sloan et al. in SIGRAPH 2002 Compute incident light from all directions off line and compress it Use compressed data for illuminating surfaces in real-time

Содержание слайда: What to do with PRT Limited real-time global illumination Basically objects mustn't deform Basically objects mustn't move Limited B(SS)RDF simulation Lambertian Diffuse Glossy Specular Arbitrary (low frequency) BRDF

Содержание слайда: Limited Animation SH Light position can move or rotate But SH lights are regarded as infinite distance lights (directional light) SH Light color and intensity can be animated IBL can be used Objects can move or rotate But if objects affect each other, those objects can’t move Because light effects are pre-computed!

Содержание слайда: SH Spherical Harmonics : are thought to be like a 2-dimensional Fourier Transform in spherical coordinates are orthogonal linear bases This time, we used them for compression of PRT data and representation of incident light

Содержание слайда: How is data compressed? PRT data is considered as a response to rays from all directions in 3D-space Think of it as 2D-space, so as to understand easily

Содержание слайда: How is data compressed?

Содержание слайда: How is data compressed? If there is a function like 2D Fourier Transform in spherical coordinates; PRT data can be compressed with it

Содержание слайда: How is data compressed? You could think of Spherical Harmonics as a 2D Fourier Transform in spherical coordinates, so as to understand easily

Содержание слайда: How data is compressed? Use lower order coefficients of SH to compress data (It is like JPEG) Use this method for compression of PRT data and light

Содержание слайда: Why use linear transformations? It is easy to handle with vector processors A linear transformation is a set of dot products (f = a*x0 + b*x1 + c*x2….) Use only MULA, MADDA and MADD (PS2) to decompress data (and light calculation) For the Vertex (Pixel) Shader, dp4 is useful for linear transformations

Содержание слайда: Compare linear transformations

Содержание слайда: Details of SH we use It is tough to use SH Lighting on PlayStation 2 Therefore we used only a few coefficients Coefficient format : 16bit fixed point (1:2:13) PlayStation 2 doesn’t have a pixel shader Only per-vertex lighting

Содержание слайда: Details of SH we use

Содержание слайда: Details of SH we use This is the SH Basis we use (Cartesian coordinate) SH[0] = 1.1026588 * x SH[1] = 1.1026588 * y SH[2] = 1.1026588 * z SH[3] = 0.6366202 SH[4] = 2.4656168 * xy SH[5] = 2.4656168 * yz SH[6] = 0.7117635 * (3z^2 - 1) SH[7] = 2.4656168 * zx SH[8] = 1.2328084 * (x^2 – y^2) SH[9] = 1.3315867 * y(3x^2-y) SH[10] = 6.5234082 * yxz SH[11] = 1.0314423 * y(5z^2 – 1) SH[12] = 0.8421680 * z(5z^2 – 3) SH[13] = 1.0314423 * x(5z^2 – 1) SH[14] = 3.2617153 * z(x^2 – y^2) SH[15] = 1.3315867 * x(x^2 – 3y^2)

Содержание слайда: Details of SH we use Our SH Shader(2bands, 1ch) code for VU1 (Main loop is 6ops) NOP LQ VF20, SHCOEF+0(VI00) NOP LQ VF21, SHCOEF+1(VI00) NOP LQ VF22, SHCOEF+2(VI00) ITOF12 VF14, VF13 LQI VF13, (VI02++) NOP LQ VF23, SHCOEF+3(VI00) NOP IADDIU VI07, VI07, 1 tls1_loop: MADDw.xyz VF30, VF23, VF15w LQI.xyz VF29, (VI03++) MULAx.xyz ACC, VF20, VF14x MOVE.zw VF15, VF14 MADDAy.xyz ACC, VF21, VF14y ISUBIU VI07, VI07, 1 ITOF12 VF14, VF13 LQI VF13, (VI02++) MADDAw.xyz ACC, VF29, VF00w IBNE VI07, VI00, tls1_loop MADDAz.xyz ACC, VF22, VF15z SQ.xyz VF30, -2(VI03)

Содержание слайда: Details of SH we use Our SH Shader(3bands, 1ch) code for VU1 (Main loop is 13ops) NOP LQI VF14, (VI02++) NOP LQI VF15, (VI02++) NOP LQ VF29, 0(VI03) ITOF12 VF25, VF13 LQ VF16, SHCOEF+0(VI00) ITOF12 VF26, VF14 LQ VF17, SHCOEF+1(VI00) ITOF12 VF27, VF15 LQ VF18, SHCOEF+2(VI00) MULAw.xyz ACC, VF29, VF00w LQ VF19, SHCOEF+3(VI00) tls2_loop: MADDAx.xyz ACC, VF16, VF25x LQ VF20, SHCOEF+4(VI00) MADDAy.xyz ACC, VF17, VF25y LQ VF21, SHCOEF+5(VI00) MADDAz.xyz ACC, VF18, VF25z LQ VF22, SHCOEF+6(VI00) MADDAx.xyz ACC, VF19, VF26x LQ VF23, SHCOEF+7(VI00) MADDAy.xyz ACC, VF20, VF26y LQ VF24, SHCOEF+8(VI00) MADDAz.xyz ACC, VF21, VF26z LQI VF13, (VI02++) MADDAx.xyz ACC, VF22, VF27x LQI VF14, (VI02++) MADDAy.xyz ACC, VF23, VF27y LQI VF15, (VI02++) MADDz.xyz VF30, VF24, VF27z LQ VF29, 1(VI03) ITOF12 VF25, VF13 ISUBIU VI07, VI07, 1 ITOF12 VF26, VF14 NOP ITOF12 VF27, VF15 IBNE VI07, VI00, tls2_loop MULAw.xyz ACC, VF29, VF00w SQI.xyz VF30, (VI03++)

Содержание слайда: Details of SH we use Engineers think that SH can be used with at least the 5th order (25 coefficients for each channel) Practically, artists think SH is useful with even the 2nd order (4 coefficients) Artists will think about how to use it efficiently

Содержание слайда: Differences in appearance The 2nd order is inaccurate However, it’s useful (soft shading) The 3rd and 4th are similar The 3rd is useful considering costs

Содержание слайда: Differences in appearance The number of channels mainly influences color bleeding (Interreflection) The number of coefficients mainly influences shadow accuracy

Содержание слайда: Differences in appearance For sub-surface scattering, color channels tend to be more important than the number of coefficients

Содержание слайда: Harmonize SH traditionally We harmonize SH Lighting with traditional lights: There is a function by which hemisphere light coefficients come from linear coefficients of Spherical Harmonics For Phong (Specular) lighting, we process diffuse and ambient with SH Shader, and process specular with traditional lighting

Содержание слайда: Side effects of SH Lighting Useful SH Lighting (Shading) is smoother than traditional lighting Especially, it is useful for low-poly-count models It works as a low pass filter

Содержание слайда: Side effects of SH Lighting Disadvantage SH is an approximation of BRDF But using only a few coefficients causes incorrect approximation

Содержание слайда: Our precomputation engine supports : Lambert diffuse shading Soft-edged shadow Sub-surface scattering Diffuse interreflection Light transport (detail later)

Содержание слайда: Materials Basic settings SH coefficient setting Computation precision (Number of rays) Low Pass Filter settings Texture setting Diffuse settings Diffuse intensity Occlusion settings Occlusion emitter Occlusion receiver Occlusion opacity

Содержание слайда: Materials Interreflection settings Interreflection intensity Number of passes Interreflection low pass filter Color settings Translucent settings Enabling single scattering Enabling multi scattering Diffusion directivity Surface thickness Permeability Diffusion amount Light Transport settings

Содержание слайда: Algorithms for PRT Based on (Stratified) Monte Carlo ray-tracing

Содержание слайда: PRT Engine [1st stage] Calculate diffuse and occlusion coefficients by Monte Carlo ray-tracing: Cast rays for all hemispherical directions Then integrate diffuse BRDF with the SH basis and calculate occlusion SH coefficients (occluded = 1.0, passed = 0.0)

Содержание слайда: PRT Engine [2nd stage] Calculate sub-surface scattering coefficients with diffuse coefficients by ray-tracing We used modified Jensen’s model (using 2 omni-directional lights) for simulating sub-surface scattering

Содержание слайда: PRT Engine [3rd stage] Calculate interreflection coefficients from diffuse and sub-surface scattering coefficients: Same as computing diffuse BRDF coefficients Cast rays for other surfaces and integrate their SH coefficients with diffuse BRDF

Содержание слайда: PRT Engine [4th stage] Repeat from the 2nd stage for number of passes After that, Final Gathering (gather all coefficients and apply a low pass filter)

Содержание слайда: Optimize precomputation To optimize finding of rays and polygon intersection, we used those typical approaches (nothing special) Multi-threading Using SSE2 instructions Cache-caring data

Содержание слайда: Optimize precomputation Multi-threading for every calculation was very efficient Example result (with dual Pentium Xeon 3.0GHz)

Содержание слайда: Optimize precomputation SSE2 (inline assembler) for finding intersections was quite efficient Example result (with dual Pentium Xeon 3.0GHz)

Содержание слайда: Optimize precomputation File Caching System SH coefficients and object geometry are cached in files for each object Use cache files unless parameters are changed

Содержание слайда: What is the problem It is still slow to maximize quality with many rays Decreasing the number of rays causes noisy images How to improve quality without many rays?

Содержание слайда: Solving the problem We used 2-stage low pass filters to solve it Diffuse interreflection low pass filter Final low pass filter

Содержание слайда: Solving the problem We used Gaussian Filter for a low pass filter Final LPF was efficient to reduce noise But it caused inaccurate result Therefore we used a pre-filter for diffuse interreflection Diffuse interreflection LPF works as irradiance caching Diffuse interreflection usually causes noisy images Reducing diffuse interreflection noise is efficient

Содержание слайда: Solving the problem Using too strong LPF causes inaccurate images Be careful using LPF

Содержание слайда: Light Transport It is our little technique for expanding SH Lighting Shader It is feasible to represent all frequency lighting (not specular) and area lights BUT! Light position can't be animated Only light color and intensity can be animated Some lights don’t move For example, torch in a dungeon, lights in a house Particularly, most light sources in the background don’t need to move

Содержание слайда: Details of Light Transport It is not used on the Spherical Harmonic basis Spherical Harmonics are orthogonal It means that the coefficients are independent of each other You can use some of (SH) coefficients for other coefficients on a different basis

Содержание слайда: Details of Light Transport To obtain Light Transport coefficients, the precomputation engine calculates all their incoming coefficients from other surfaces It means that Light Transport coefficients have the same Light Transport energy that the surfaces collect from other surfaces And surfaces which emit light give energy to other surfaces Without modification to existing SH Lighting Shader, it multiplies Light Transport coefficients by light color and intensity They are just like vertex color multiplied by specific intensity and color

Содержание слайда: Details of Light Transport They are automatically computed by existing global illumination engine When you set energy parameters into some coefficients, a precomputation engine for diffuse interreflection will transmit them to other surfaces

Содержание слайда: Result of Light Transport

Содержание слайда: Image Based Lighting Our SH Lighting engine supports Image Based Lighting It is too expensive to compute light coefficients in every frame for PlayStation 2 Therefore light coefficients are precomputed off line IBL lights can be animated with color, intensity, rotation, and linear interpolation between different IBL lights

Содержание слайда: Image Based Lighting IBL light coefficients are precomputed in world coordinates It means they have to be transformed to local coordinates for each object Therefore, IBL on our engine requires Spherical Harmonic rotation matrices

Содержание слайда: SH rotation To obtain Spherical Harmonic rotation matrices is one of the problems of handling Spherical Harmonics We used "Evaluation of the rotation matrices in the basis of real spherical harmonics" It was easy to implement

Содержание слайда: SH animation Our SH Lighting engine supports limited animation Skinning Morphing

Содержание слайда: SH skinning Skinning is only for the 1st and 2nd order coefficients They are just linear Therefore, you can use regular rotation matrices for skinning If you want to rotate above the 2nd order coefficients (they are non-linear), you have to use SH rotation matrices But it is just rotation Shadow, interreflection and sub-surface scattering are incorrect

Содержание слайда: SH morphing Morphing is linear interpolation between different Spherical Harmonic coefficients It is just linear interpolation, so transitional values are incorrect But it supports all types of SH coefficients (including Light Transport)

Содержание слайда: Future work Using high precision buffer and pixel shader!! More precise Glare Effects in optics Natural Blur function not Gaussian Diaphragm-shaped Blur Seamless and Hopping-free DOF along depth direction OLS using HDR values Higher quality slight blur effect

Содержание слайда: Future Work Distributed precomputation engine SH Lighting for next-gen hardware Try: Thomas Annen et al. EGSR 2004 “Spherical Harmonic Gradients for Mid-Range Illumination” More generality for using SH lighting IBL map Try other methods for real-time global illumination

Содержание слайда: References Masaki Kawase. "Frame Buffer Postprocessing Effects in DOUBLE-S.T.E.A.L (Wreckless)“ GDC 2003. Masaki Kawase. "Practical Implementation of High Dynamic Range Rendering“ GDC 2004. Naty Hoffman et al. "Rendering Outdoor Light Scattering in Real Time“ GDC 2002. Akio Ooba. “GS Programming Men-keisan: Cho SIMD Keisanho” CEDEC 2002. Arcot J. Preetham. "Modeling Skylight and Aerial Perspective" in "Light and Color in the Outdoors" SIGGRAPH 2003 Course.

Содержание слайда: References Peter-Pike Sloan et al. “Precomputed Radiance Transfer for Real-Time Rendering in Dynamic, Low-Frequency Lighting Environments.” SIGGRAPH 2002. Robin Green. “Spherical Harmonic Lighting: The Gritty Details. “ GDC 2003. Miguel A. Blanco et al. “Evaluation of the rotation matrices in the basis of real spherical harmonics.” ECCC-3 1997. Henrik Wann Jensen “Realistic Image Synthesis Using Photon Mapping.” A K PETERS LTD, 2001. Paul Debevec “Light Probe Image Gallery” http://www.debevec.org/

Содержание слайда: Acknowledgements We would like to thank Satoshi Ishii, Daisuke Sugiura for suggestion to this session All other staff in our company for screen shots in this presentation Mike Hood for checking this presentation Shinya Nishina for helping translation The Stanford 3D Scanning Repository http://graphics.stanford.edu/data/3Dscanrep/

Содержание слайда: Thank you for your attention. This slide presentation is available on http://research.tri-ace.com/