RE: [Algorithms] Dynamic Gamma / Tone Mapping
Brought to you by:
vexxed72
From: Wolfgang E. <wengel@RockstarSanDiego.com> - 2005-12-02 18:45:54
|
<<< What VALVE did on their last "not-quite-HDR show" could be a simple gamma add operation. <<< I believe they used HDR textures that are good for 16 different exposure values and as far as I can see they use the same Erik Reinhard tone-mapping operator like most people do. They might work in gamma 1.0, but other than this I would not think that there is something that is surprising from a technical point of view.=20 =20 Overall they managed to get the whole art workflow running and release a complete level that looks great.=20 =20 I saw your website before. I think one guy from your company featured your compressed HDR. =20 - Wolf ________________________________ From: gda...@li... [mailto:gda...@li...] On Behalf Of Emanuele Salvucci Sent: Thursday, December 01, 2005 9:41 AM To: gda...@li... Subject: Re: [Algorithms] Dynamic Gamma / Tone Mapping =20 I agree with the tools. In fact we have custom ones...and use Lightwave as it's native HDR. (sky generation, volumetric particle baking, to name a couple) I also agree on the limited dynamic range needed. The original St.Peter's basilica probe has got a maximum luminance value of ~1100. Not sure what you mean with "color contrast" ...but if you can generate the whole data in HDR and keep it in realtime, you shouldn't experience such a loss. =20 What VALVE did on their last "not-quite-HDR show" could be a simple gamma add operation. Once you have the overall frame's luminance, as said by someone else previously, you could proceed like this: =20 - RTT the framebuffer - Pass it to a gamma operator (pixel shader) just once - Add the result on a fullscreen quad N times =20 The gamma operator is obviously the key to the desired effect. You might want to have a function that enhances bright values and darkens midtones when you get a high overall frame luminance, or maybe the other way around, to never get over-exposed nor pitch-black lighting....but the latter is against the current common "desired look", it seems. :) =20 Unless they've dropped lightmapping, I doubt they've used real HDR data in that demo. =20 As you can see from our website, we instead manage HDR lightmaps, together with dynamic lighting. =20 =20 =20 =20 Emanuele Salvucci Maya|Lightwave Game Technical Artist Lscript developer =20 www.forwardgames.com <http://www.forwardgames.com>=20 ema...@fo... =20 "#3. He causes things to look different so it would appear time has passed." ________________________________ =20 =20 =20 ----- Original Message -----=20 From: "Wolfgang Engel" <wengel@RockstarSanDiego.com <mailto:wengel@RockstarSanDiego.com> > To: <gda...@li... <mailto:gda...@li...> > Sent: Thursday, December 01, 2005 5:23 PM Subject: RE: [Algorithms] Dynamic Gamma / Tone Mapping The idea is to choose 256 luminance values out of the 64k that are possible by using 16-bit textures. Choosing the 256 values can happen over this whole range and under different criteria. You have a middle-grey value that helps you to emphasize a specific range of luminance values and with the light adaption result, you move the 256 values you choose up and down through the 64k luminance value range. So the main idea is to choose the best suitable luminance range that fits to the scene. The practical problems are - you do not really have 64k luminance values anywhere. The reason for this is that we do not have the tools and teams do not have necessary the experience on how to do this. So you end up with a much lower range of values. - as already mentioned: color contrast gets lost - what I can see in some 360 games now: the light adaption process is not very precise it stutters sometimes =20 I think the most difficult part about HDR/tone-mapping is to establish an art pipeline that can produce predictable results. The problem starts just by using Photoshop. Try to open up a HDR texture with CS2 and save it ... it took some time until this really worked. At the same time we tried the latest beta of Photogenics but while trying to adjust the gamma value we bumped into a bug ............. =20 One of the things I would love to hear is, how VALVE did that for Lost Coast, but I can understand that they do not want to share this :-) ________________________________ From: gda...@li... <mailto:gda...@li...> on behalf of Emanuele Salvucci Sent: Wed 11/30/2005 7:01 PM To: gda...@li... <mailto:gda...@li...>=20 Subject: Re: [Algorithms] Dynamic Gamma / Tone Mapping =20 A question about the model based on the eye perception, and new consoles. =20 Considering X360 and PS3 are HDTV-ready and HDTV screens usually have far higher contrast and luminosity than standard PC monitors or TVs, is it useful to tone map with that model ? =20 At the end of the day, isn't an HDR scene well represented by a 1000:1 contrast for most games...? =20 I'm suspecting it's gonna be a waste of cycles. =20 =20 =20 Best, =20 Emanuele Salvucci Maya|Lightwave Game Technical Artist Lscript developer =20 www.forwardgames.com <http://www.forwardgames.com> <http://www.forwardgames.com <http://www.forwardgames.com> >=20 ema...@fo... <mailto:ema...@fo...>=20 =20 "#3. He causes things to look different so it would appear time has passed." ________________________________ ----- Original Message -----=20 From: Wolfgang Engel <mailto:wengel@RockstarSanDiego.com <mailto:wengel@RockstarSanDiego.com> > =20 To: gda...@li... <mailto:gda...@li...> =20 Sent: Thursday, December 01, 2005 1:42 AM Subject: RE: [Algorithms] Dynamic Gamma / Tone Mapping Yep, the paper title is "Dynamic Range Reduction Inspired by Photoreceptor Physiology". It is published in the IEEE 2005 Vol. 11, No.1 January/February 2005, page 13. A short google search only showed up the IEEE website where you can buy the paper ... I think I bought it from there. Having bought my third paper from this website now, I am thinking about a membership ... - Wolfgang ________________________________ From: gda...@li... <mailto:gda...@li...> [mailto:gda...@li...] On Behalf Of Rowan Wyborn Sent: Wednesday, November 30, 2005 2:32 PM To: gda...@li... <mailto:gda...@li...>=20 Subject: RE: [Algorithms] Dynamic Gamma / Tone Mapping do you have links to either of those papers online? (siggraph or 2005 paper)=20 :) thanks, rowan ________________________________ From: Wolfgang Engel [mailto:gda...@li...] On Behalf Of Wolfgang Engel Sent: Thursday, 1 December 2005 3:52 AM To: gda...@li... <mailto:gda...@li...>=20 Subject: RE: [Algorithms] Dynamic Gamma / Tone Mapping I think good ideas for contrast improvements can be found in Erik Reinhardt's 2005 paper ... just forgot the name, but he also talked on SIGGRAPH this year about it. You might for example interpolate the luminance of a pixel with the scene luminance or you might store luminance not for RGB per scene, but for each color channel separately. This should help with contrast. Anyone tried this? - Wolfgang |