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not clear on the HDRI topic......
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not clear on the HDRI topic...... // Roundtable
Post by memevertical // Aug 10, 2006, 5:21am
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memevertical
Total Posts: 20
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What is HDRI exactly? can someone bring some clarity to me on this subject? Thanks you guys :) |
Post by spacekdet // Aug 10, 2006, 5:26am
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spacekdet
Total Posts: 1360
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Give this a lookie-loo. (http://en.wikipedia.org/wiki/HDRI) |
Post by Birdnest // Aug 10, 2006, 5:27am
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Birdnest
Total Posts: 152
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I'm not exactly sure...
But I think it involves how light interacts with objects using reflectent shaders and such. Or basically how light interacts with any object I guess...
But HDRI talk confuses the hell outta me too lol.
Somebody answer this question, I would like to know more detail too!! |
Post by Bobbins // Aug 10, 2006, 5:28am
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Bobbins
Total Posts: 506
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Put simply, it's an image format that allows for more colour and brightness information to be stored than in a standard 24 bit file format.
A 24 bit file format only allows 8 bits for each of the Red, Green and Blue channels, so there can only be 256 levels of Red, Green and Blue (8 bits means 256 different values) giving a total of 16.7 million colours (256x256x256). By assigning more than 8 bits for each channel you can have a much larger range of colours between pure black and pure white.
The result is a smoother gradient of colours and a higher dynamic range, hence the name High Dynamic Range Image. |
Post by Birdnest // Aug 10, 2006, 5:53am
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Birdnest
Total Posts: 152
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Put simply, it's an image format that allows for more colour and brightness information to be stored than in a standard 24 bit file format.
A 24 bit file format only allows 8 bits for each of the Red, Green and Blue channels, so there can only be 256 levels of Red, Green and Blue (8 bits means 256 different values) giving a total of 16.7 million colours (256x256x256). By assigning more than 8 bits for each channel you can have a much larger range of colours between pure black and pure white.
The result is a smoother gradient of colours and a higher dynamic range, hence the name High Dynamic Range Image.
This helps too! :) |
Post by Steinie // Aug 10, 2006, 6:00am
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Steinie
Total Posts: 3667
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Is it safe to assume that if you use HDRI you will loose alpha masking? Doesn't that use the bits above 16.7 million? |
Post by Bobbins // Aug 10, 2006, 6:10am
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Bobbins
Total Posts: 506
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Different thing Steinie, HDRI actually stores the information as floating point values and not integers so the "bits above 16.7 million" is meaningless. |
Post by TomG // Aug 14, 2006, 2:54am
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TomG
Total Posts: 3397
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As a note, although HDRI is an image, it is actually used for lighting in 3D applications.
That is, the image is used to generate / calculate the lighting in a scene, and the reflections / refractions in the scene too.
The primary use is to capture a real-world location and render objects so they appear to be in that real-world location. As well as capturing a higher dynamic range (the HDRI course does a great job of explaining that in details btw), the images also capture the whole surroundings, not just an image in one direction like a regular photograph. This results in the image being in an unusual format, either panoramic, or cross, or spherical.
Note that the concept of high dynamic range is easily seen - take a picture with bright sky and dark shadow visible in it. For one picture, use a small aperture, and for another, use a large aperture. You will find in one picture you get detail in the shadows, but the sky bleaches out to be totally white. In another, the sky will be a nice blue (or grey, or whatever color it should be), but the shadows are totally black.
An HDRI image contains BOTH the correct saturated sky and correct saturated shadows, since it contains enough range in the data to handle both. Computer monitors and digital cameras (and film cameras) only allow for a limited section of that range to display at once. Until HDRI that is.
So that's the quick and simple tech details. All in all it adds up to this though - easy way to get realistic and detailed lighting and reflections / refractions in a render.
HTH!
Tom |
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