Luminance Equalization

[Jeff Mottle]

Here is a great tutorial to fix luminance equalizatino problems in your renders. I've used it a few times and works great!

 

http://www.3drender.com/light/EqTutorial/index.htm

[STRAT]

fantastic Jeff, i'm often struggling with this problem. thinking about it this is also a nice way (with a bit of fiddling about) of producing HDR images.

[Jeff Mottle]

Actually I'm not sure if this will work. HDR needs more color info and you would be cheating it. It would be like just resampling an image to be bigger without the pixel info to support it. I believe the actual photographed images needs to be bracketed rather than generating the brakets from a single image. As the saying goes, garbage in garbage out. I suspect it will work, but won't be as accurate as a true HDR image. Maybe I'm wrong...somebody correct me.

 

thinking about it this is also a nice way (with a bit of fiddling about) of producing HDR images.

[STRAT]

hmmm, Jeff you may be right, perhaps i need correcting

 

i was under the assumption HDR images held more than the normal gamut of visible lighting info generally held in a normal photo, but how can this be physically possible in a picture on the screen? what you see is what you get isn't it? and if thats the case it's quite easy to fake (as i sometimes easily do) HDR images in photoshop.

 

or does a HDR image hold more info that we cant see? i some how doubt it.

 

I've held a poll on another forum before now regarding HDRI and how valid in ppl's work it is.

Personally i think it's a heck of a lot of hot air, completely over-hyped and one of the most easily faked effescts in CGI. i got similar views to mine.

 

what do ppl think?

[TAKA]

wow, i stumbled on this tut like 4 or 5 months ago.....good to see it's still there...

 

cheers

[nisus]

Hi strat,

 

I read a good article on creating HDRI a few months ago. To make those one should take three exactly the same photo but the first one normally lit, the second over exposed, the third under exposed. Info from these three images are than combined into one image with good detail in light and shadow areas. Got to find that article again, but I'm off for a concert now: Dansmall, englishirishfolk

 

rgds

 

nisus

[Ernest Burden III]

Originally posted by nisus:

one should take three exactly the same photo but the first one normally lit, the second over exposed, the third under exposed. Info from these three images are than combined into one image with good detail in light and shadow areas.

Please do find the article. The problem comes in the combining. Photoshop can work in either 8 bit color or 16 bit color. You would need the 16 bit mode to get a true HDRI I would think. 8 bit only has 256 levels of luminence per channel, while 16 has 65K levels. But you cannot composite or layer or copy/paste images in 16 bit mode. So different software would be the order. I'm not sure which, though.

[Jeff Mottle]

Everything you should need is here:

 

http://www.debevec.org/HDRShop/

[nisus]

Hi Ernest,

 

A bit late, but here it is: http://www.cs.huji.ac.il/~danix/hdr/

 

rgds

 

nisus

[STRAT]

thnx chaps, got my head round it now. posting in maxforums.org also cleared some stuff up.

 

i've read this blurb for ages, but it still doesn't explain exactly the process of how and wat HDR actually is.

 

allot of ppl bandy round their supposed HDRI images but how many ppl actually do true correct HDRI? or even know exactly how to use it? fewer than they think i suspect.

 

a true HDRI image CANNOT be created and compiled in photoshop and it needs to be 32 bit and as yet no true 32 bit image processing apps exist. (i dont think).

A HRDI rendering shader pulls together 3 or more photos of the same subject/shot each taken at different exposures to create the high and low dynamic light ranges, and renders them out into your final image.

 

This effect is sooooooooo easily faked i doubt weath most ppl (if any) would even spot the difference between a fake and the real HDRI piccy.

 

and as for HDR or image based lighting? another buzz word describing sommit thats been a basic render technique for ages. nothing special.

[Jeff Mottle]

There is one that I know of: http://www.idruna.com/

 

a true HDRI image CANNOT be created and compiled in photoshop and it needs to be 32 bit and as yet no true 32 bit image processing apps exist. (i dont think).

 

[ October 11, 2002, 07:50 AM: Message edited by: Jeff Mottle ]

[Ernest Burden III]

Thanks, Jeff. That package looks very good.

 

Just what I need...another $700 software to buy.

[Brian Cassil]

besides the idruna software (which is expensive) Paul Debevec's free app hdr-shop is supposed to allow you to create and manipulate in true 32 bit. The only problem is I haven't ever been able to download it! The download page on Paul's site has been down for ages. I even asked Paul himself about this at siggraph and he said the link would be taken care of but that has been months now. If anyone has info on how to get a hold of this app please pass it on because I would really like to see how it works.

[nisus]

Hi strat,

 

Indeed fakes are all around us... But as you've been doing your homework on HDRI, what is up with the lightprobes-thing? (I thought one is supposed to take photographs of a lightprobe to light a scene 'correctly' using HDRI...)

Didn't the 'fiat-lux'-animation made extensive use of HDRI? Anyone knows?

 

rgds

 

nisus

[Ernest Burden III]

I would like to look at some 'properly' done light maps and get a sense of how they relate to the scene...and draw my own. I always used to do my own lighting and reflection calcs by eye (in hand-done art), so why not do my own for image-based lighting? It really could be interesting, and a very quick way to light a scene.

 

None of the software I use has that, but a friend is getting into c4d which does, so I may try in on his machine.

 

Yet another possible hybrid technique.

 

(I thought one is supposed to take photographs of a lightprobe to light a scene 'correctly' using HDRI...)nisus

[ingo]

Since i work with HDR images for some time now (mainly only the well known images from Paul Devbec) i want to add my two cents:

 

First i used HDR images as a backdrop for raydiosity renderings, its just a simple globe mapping rendering without any lights. They look simply amazing, but as always because of the looong render times its not usable for architectural renderings. Well, not now.

 

My second daily experience is when i am able to move the black and whitepoint on a 96 Bit rendering its simply amazing what you can do with it. You have a dark rendering, no problem, just move the sliders and your rendering looks great; and nothing compared to do the same in Photoshops 24 Bit color space (can you say banding).

 

Since many of the now appearing new renderers render in 128 Bit (yes a truely 32 Bit Alpha channel) HDR is definitly no buzzword.

 

HTH

 

ingo

www.im-graphics.com

 

P.S.: When you look at my website in the test-renderings there are a few HDR renderings using the HDRI as a global map in GI; the glassy thing for example.

[STRAT]

well, i've been doing a fair bit of research recently too and am now jenned up on the actual theory of creating them, more or less.

 

i still think HDRI is easy to fake. there are very few ppl around that i know of that do true HDRI rendering.

go look at this chap, he does it -

 

http://www.trinisica.com/

 

i've seen your site and the test renderings you mention ingo, and no offense intended here but they all look like general run-of-the-mill every day test renders. Nothing that looks remotely like real (or even fake) HDRI rendering. All VERY easily faked and achieved within minutes.

 

Real HDRI is impressive, but ppl still use the word and phrase like they know exactly what they're talking about and how use it properly.

 

HDRI is a real thing, but it's also a falsly over-used buzz word.

 

[ October 18, 2002, 07:53 AM: Message edited by: STRAT ]

[ingo]

Hi Strat,

 

i've read this strange article before. From what you can see in the reflection pictures you cant fake HDR reflections, especially if you use a 24 Bit rendering engine. You can only move a 24 Bit dynamic range of the picture up or down (i think that is what you call the faked HDRI). If you really want to use it you need a rendering engine capable of more than 24 Bit, otherwise youre right, its not very useful (i think Brazil uses more than 24 Bits, so wait when their stand alone renderer is ready). Not to mention that this obviously slows down the rendering time.

For me its still a big plus to render with Lightwaves 128 Bit renderer and than move the black and whitepoint in LW to tweak the settings.

But as always there are many people using those nice buzzwords to sell their stuff. At least your output is limited to the 24 Bit, and if you print things you even have a smaller colorspace.

 

ingo

[kid]

HDRI is easily faked in stills but the way HDRI interacts with motion blur in animation cannot be faked using low dynamic images.

 

[ October 18, 2002, 10:16 AM: Message edited by: kid ]

[STRAT]

Originally posted by ingo:

Hi Strat,

 

i've read this strange article before. From what you can see in the reflection pictures you cant fake HDR reflections, especially if you use a 24 Bit rendering engine.

 

ingo

but thats the whole point of the word 'fake'. you can fake the hdr reflections. with ease.

 

ok, so it's not true hdri with 24 bit editing, but thats the point of faking it. you'd never know the difference.

 

But, Kid also has a valid point. trying to fake them with animated MB reflections is another challenge completely.

 

on the other hand tho, motion blur (like DOF also) is artificial anyway, it's only a camera by-product.

In real life mb and dof dont exist either

[kid]

on the other hand tho, motion blur (like DOF also) is artificial anyway, it's only a camera by-product.

In real life mb and dof dont exist either [[Wink]]

 

My eyes are cameras though

[nisus]

Ow... I have a wonderful real-life DOF without my glasses...

 

nisus

[ingo]

>>> you can fake the hdr reflections. with ease.

 

How ? I've never seen it and on the website you mentioned they tried it by using a HDRI with higher luminosity which gave no convincing result since you loose detail in the left red ball.

But youre right when using a HDRI as global map for GI renderings, you wont see much difference compared to a normal 24 Bit as a map.

 

ingo

High Dynamic Rants

[ingo]

And now something completly different...

 

In the beginning of this thread Jeff mentioned a website where they explain how to equalize luminance in a picture, useful for texture maps, do you remember ?

 

Ok, here is a better way :

 

1. Open the picture in PS and switch to Lab Mode, if youre not already.

 

2. Click on the lighting (? no PS here so just a guess) channel so you have now only the channel with the black and white information. That avoids a change in the colors compared to the way they did it on the website.

 

3. Now choose the highpass filter in the last filter section (with offset filter...) and play with the slider till the lighting is equal. It needs some testing to get good results.

 

4. Make some adjustment to get back some detail with curves or levels.

 

Thats it. Hope you like it.

 

ingo

[STRAT]

cheers ingo, i'll try that out in work on monday morning