I'm sure this question has been answered a million times, but I haven't seen it answered, so I'm asking it again. =) Maybe you can just point me to a forum thread or article or something real quick. I would like to know the theory of High Dynamic Range. As I currently understand it, HDR is a post-processing effect that copies an image, makes transparent anything below a certain luminosity, blurs it extensively, then places it over the original image. This produces "glare" effects, as well as allowing a 3D image to have large areas of full white, making it appear brighter and more realistic. Am I correct? Or is this something else entirely?

Attached Link: http://www.debevec.org/

Actually,..........I know it as HDRI(High Dynamic Range Imaging), wherein you use a specially processed image(HDRI or HDR) to provide a light source for your scene. Higher end apps can make use of this process, 3D Studio Max, C4D and others. See attached link for more info. You can fake HDRI in Bryce(do a forum search for "Fake HDRI") but you cannot do true HDRI. Vue 5 I does have an HDRI option but as to whether it's true HDRI, I have no knowledge. Hope that helps.

well, thats' one effect, anyway..;)

Don't wory shiny, I've been just as confused as you are. So far I guess I've just learned to keep lighting as simple as possible. Still, not the best approach. Maybe I'll start getting into this HDRI stuff too.

lol@pakled

oh, and as i understand HDRI, it's basically a sphere around teh scene. bryce can fake it, but basically the image applied over the sphere has colors. like the gray of a balcony, etc. that is translated into gray, blue, red, etc. light. and it lights the scene without any need for external lighting sources. my understanding, anyway. haven't looked it up much because bryce can't handle it in its native format. drac

Normal 8-bit images only have 255 values for red, green, and blue. an hdr image contains unlimited values for each number, but also contains a separate luminance (brightness) value in addition to the colors that represents the actual intensity of light at that point. These values are usually calculated by analysing several exposures of the same scene, taken in the exact same position on a tripod. The software (either photoshop or hdrshop), looks at each pixel of each exposure and uses the difference between exposures to determine the actual brightness at that point. With only 255 bits per color, you can only have 255 levels of brightness held in an image. In real life, the sun is more than 2 million times as bright as "black," and an hdr image can represent this. Nor it's useful because it actually lets you adjust exposure without changing the contrast of the image. You can just slide back and forth between under and over exposed until you find the right middle ground. When you import an hdr file into a 3d program, the brightness values are actually mapped as light sources in a 3D spherical space. Thus, the image actually casts light according to the actual values in the scene. This is very useful for mimicing real-life lighting scenarios, and is indespensable for accurate compositing, at it allows you to completely match a computer generated element into live footage.

Also worthy of note is that high dynamic range images can't be distinguished from regular images on normal displays, because normal displays can't output enough light to achieve the 200:000:1 or higher contrast ratios needed. Brightside technologies has released the worlds first commercially available high dynmaic range display, seen here: http://www.brightsidetech.com/

"With only 255 bits per color, you can only have 255 levels of brightness held in an image." Errm -- not actually true. Since there are 3 colours (Red, Green and Blue), and each has a range of 0-255, the brightness range is 0-255 for each colour. So the total luminosisity is in the range 256 x 256 x 256 = 16777216. The brightness varies between Red=0, Green=0, Blue=0 (black) to R=255, G=255, B=255 (white). What is lost is the shades in between.. The average human eye can distinguish differences in colour/brightness to approx 1 part in 25,000,000. So I suspect that no-one really misses anything (with or without hi-dri). OTOH: hi-dri can sometimes add some nuances which add to th flavour (ading a touch here and there). For total perfctionists, this is a must-have. For simpletons like myself, it just not worth the effort.. Cheers, Diolma (No offence intended to anyone)

I am not referring to color combinations, there are 16.7 million of those in rgb images. What I am saying is that the maximum difference between black and white is only 255 levels, that is between rgb 0,0,0 and rgb 255,255,255. High dynamic range can represent white as "theoretically," rgb 1,000,000 100,000,000 1,000,000, so that when you display the image on a high dynamic range display or adjust the exposure, the image behaves much more like real life. In the real world, not all "bright" things are the same brightness. hdr allows you to express how bright things are very accurately, while normal 8-bit rgb images cap all bright things at one value, which is pure white.

Actually, HDRI does have a certain appeal,........however, this can be faked with a high degree of accuracy in Bryce using image domes and light domes. Rendertimes can be prohibitive though and it can melt lesser powered machines into a lump or molten goo. Still, I like HDRI and use it in my work frequently, like I said it has a certain appeal and in C4D is relatively easy to use(see attached image). This image was done in C4D V8.1,........it took about 10 minutes to build the models and texture them and about 15 minutes to render on medium high settings. (Sorry for the sacreligeous non-Bryce content).

Thanks very much, very helpful information. lol@pakled, how very true. =) sackrat- Looks pretty cool. I've considered getting C4D, but I'm going to be learning Maya in school and that's enough cash expenditure for me. I may also have to get 3DS Max, so much cash flow going on here, cash flow away from me that is. =) As for doing a forum search, I'd prefer to try and develop my own techniques, which is why I would like to understand exactly what it is and how more powerful programs like C4D do it. I went ahead and did a forum search to see what I was looking at, and found the technique drac presents. It seems to me that this would not be useful in a very wide variety of circumstances, never mind the fact that you have to download images to use from the internet (something I'm just not willing to do), or learn photography, which may come later for me in college. madmax- Hmm... so HDR just means that it expects a lot more colors to be available, colors that aren't there on the monitors? Then these colors are replaced with white because they aren't there? Then, at least for a regular monitor, HDR seems to me to be a method by which we can create more realistic colors. =)

Woo, this thread has some good info in it! I'm bookmarking this, and going to start experimenting. @ Sackrat, your c4d image ... those light reflections on the dome glass was done by putting a sphere around the scene? What exactly do you do to get stuff like that to happen, and what does that have to do with color intensities and big numbers?

@moongoat,........yeah, basically that's how I do HDRI in C4D,......you use 2 spheres to enlose the scene, 1 seen by the global illumination(GI) and 1 seen by the camera(Visible). Since this is a Bryce forum I'll not go into it any further, however if you want to know the technique for C4D, email or IM me and I'd be glad to send you some more info on the process. As far as the way to fake it in Bryce, search this forum for "Fake HDRI" and you should find some threads that will help.

HDRI illumination is a simple trick for taking the power and speed of the Cinema render engine and turning it into bryce like render times (grin).

Poser 6 has a bunch of HDRI lighting sets. I'm sure they'd be really cool if I knew how to use them properly. Whenever, I try it, my whole scene just looks dull. I'm talking about the GI here, so I'm not sure if its the same thing.

Message edited on: 12/10/2005 21:52

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Attached Link: http://www.hdri.at/en/hdri_en.htm

Poser 6 doesn't use HDR images. The images it uses are low dynamic range (LDR), such as .jpg, .bmp, etc. Here's a good explaination of what HDRI is, and there's a link to some comparison images of LDR vs. HDR at the bottom of the page. Basically, HDR is a type of image-based lighting (IBL), which contains more brightness information than regular image formats, allowing for brighter brights and darker darks to be used as a lightsource.

Thanks very much toolz--this is exactly what I had in mind when I started this thread in the first place. I'm bookmarking this thread as well. It does seem to me, however, that in the absence of a good HDR renderer (such as those of us using Bryce), a reasonable substitution could be made (though obviously nowhere near as good as the real thing) using a paint program and a combination of color/contrast filters and the "blooming" method I described above. I believe that this is how they simulate HDR in next-gen video games such as Oblivion and Half-Life2: Lost Coast. Obviously real HDR is out in real time =)

Yes you can just bump up the contrast of an image to make it appear like an hdr, but you will not get the added effect of it actually casting light into the scene, so you'll only see the effect if you have lots of reflected objects.

Here's an action I made for photoshop that will give you a "bloom" effect on highlights:
Save it to disk and in photoshop, find the actions pane, click the little arrow in the upper left of it, and select "load actions." Then broswe for the file and load it. It will appear in the list under "bloom fx." Select the action and press play :)

Here is an example scene including a "fake" hdr reflection dome:

Message edited on: 12/11/2005 12:57

"High dynamic range can represent white as "theoretically," rgb 1,000,000 100,000,000 1,000,000, so that when you display the image on a high dynamic range display or adjust the exposure, the image behaves much more like real life." So you have to have a "high dynamic range display" for any of this to have any effect? Not just a normal PC and/or video card? Just want to know (so I can but out of this thread if it doesn't apply to me).... Cheers, Diolma

"Yes you can just bump up the contrast of an image to make it appear *like* an hdr, but you will not get the added effect of it actually casting light into the scene, so you'll only see the effect if you have lots of reflected objects."

Indeed. Here's my first attempt. Like you said, not true HDR, but HDR cannot be achieved correctly in Bryce, so it's all fake anyways. Top is original render, bottom is with postprocessing. I used both the "blooming" method I described above, and a sort of "reverse blooming", in which I took the darks instead of the lights and used burn for the layer combinations. This effectively increased the contrast in the image without losing much if any detail. It's a pretty subtle difference; I should play around with it a bit more.

Message edited on: 12/11/2005 15:51

Diolma, yes to see the full range of a high dynamic range would be impossible, as there can be an infinite range of light, which no display can reproduce. Current displays have a brightness of no more than 300 cd/m2 and a black of no less than 0.5 cd/m2. for the contrast ratio, divide the brightness by the blackness, so you get 600:1 for high end displays. In the real world, the sun is considered to be about 10,000 foot-candles on a bright day. Converted to the same measurements, a high-end display today only outputs 27 foot-candles. A dark alley is probably around four foot-candles. Therefore, there needs to be an effective contrast ratio of at least 2500:1 to display just the relative intensity of each area. That also means that there needs to be at least 2500 values from black to white in order to display the range of illumination between the sunlight and shade. Current 8-bit displays can only represent 255 gradations, so on a high-dynamic range image containing such data, 90% of it will not be dispalyed. BUT, just because you can't see it doesn't mean it can't work for you. 3D software (not bryce, but maybe version 6 eh?) can read the intensities in the HDR file an use that to illuminate a scene according to real world illumination scales. Granted, your render will inevitably be low dynamic range, because they are being rendered in 8-bit. But since all other things have limited dynamic ranges as well, either digital photos or film, the image will appear more realistic.

Glad to see you back here Max! Yes, I know that you are in University and studying our humble art to the extreme. Thank you so much for your feedback. Nice to hear from you again. Miss you at the old museum. How's California treating you?

LOL @ MadMax (I remember them Ozzie movies..) OK - so without special hardware etc, I can't reproduce HIDRI. And even if I could, it would only introduce some very special nuances that 99.999% of the viewing public would miss. I think I'll give it a miss, til the technology (and my wallet ) catches up:-)) I admire your enthusiasm tho.. Cheers, Diolma

haha yes, just give it a few years and the debate will be between hdri and sdri (super-dynamic range imagery) ;-P Quest I'm doing very well, still in new york tho we still have a few days left in school before winter break. It's beena crazy semester tho. My girlfriend just arrived from England! (and yes, I've met here in real life before ;-)) How have you been?

Doing good my friend, glad youre doing well. Sounds like youre going to be very busy with the other half coming in to visit. Man, youre always on the move. Good to hear from you.