Author Topic: exposure times for HDR  (Read 6357 times)

Offline ravex

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exposure times for HDR
« on: February 21, 2009, 06:02:21 PM »
Hi guys.
i want just ask. how in render or camera get multiple exposure times for build HDR Image like This

this sample created from 3 different exposure times
1/750, 1/180 and 1/45s.




how get this image effect in TG2?

Offline matrix2003

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Re: exposure times for HDR
« Reply #1 on: February 21, 2009, 06:37:13 PM »
Hi!  Here is what I do!

Save your original image as a .EXR file, not .bmp.  Open in an image editor and adjust exposure and or gamma settings till you find the desired level you are looking for.  Save as a .jpeg with a unique file name that reflects the exposure level (plus, minus, base - whatever)  Do this for three images at the exposures that resemble what you would normal use for an HDR image. This part is up to your personal taste.  I do not have hard numbers, just do what looks appropriate for a three exposure HDR. Open in Photoshop, Photomatrix or what ever HDR software you would normal use and edit away!  My only other advice is less is more.  HDR can blow things out of whack and make for a lot of noise or blown out skies.  Tread lightly!  Hope that helped.   -  Bill .
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Offline PorcupineFloyd

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Re: exposure times for HDR
« Reply #2 on: February 21, 2009, 06:43:14 PM »
Set exposure on 0 and save your render as OpenEXR format.

Tweak exposure as desired and save as 8 bit image multiple times with different exposures and then merge to HDR.
Or manipulate in 32 bit.

Offline Oshyan

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Re: exposure times for HDR
« Reply #3 on: February 21, 2009, 07:26:36 PM »
EXR *is* an HDR format and TG2 renders natively in "high dynamic range"/high accuracy. There's no need to compose an HDR out of multiple image exposures. Just save the original render as EXR directly and then convert to your HDR format of choice, adjust exposure, etc. as desired. It can be processed just like a merged HDR image from photos, for example with tone mapping in Photomatix, etc.

- Oshyan

Offline matrix2003

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Re: exposure times for HDR
« Reply #4 on: February 21, 2009, 09:30:34 PM »
Hi Osh.
I have been doing that for a while now, -direct from EXR in photomatrix.  But always trying to push the limits,  I have gotten some real surreal looking renders depending on how you tweak the individual files.  More artistic freedom than just contrast, gamma and brightness.
- Bill . 
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Offline mt_sabao

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Re: exposure times for HDR
« Reply #5 on: February 22, 2009, 12:49:54 AM »
just like Oshyan said, tonemap it directly from the exr (which is already hdr 32bit) in photomatix if you have it. or in photoshop, exr is a 32 bit format, just go image>mode>8bit so now in converting from 32bit to 8bit you're presented with the tonemapping controls. Choose local adaptation from the method, which is the one that provides you with more controls.

but still, if you can afford it, photomatix is much cooler, much more control and nicer results.

Offline matrix2003

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Re: exposure times for HDR
« Reply #6 on: February 22, 2009, 01:10:26 AM »
.EXR into Photomatrix.
« Last Edit: February 22, 2009, 01:15:15 AM by matrix2003 »
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Offline rcallicotte

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Re: exposure times for HDR
« Reply #7 on: February 22, 2009, 03:08:24 AM »
.EXR in Photomatix.  Right.
So this is Disney World.  Can we live here?

Offline matrix2003

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Re: exposure times for HDR
« Reply #8 on: February 23, 2009, 08:39:50 PM »
Well if there are infinite settings going from 32 bit to an final 8 bit image, where is the benefit of calling the final image "HDR"?  The common use of hdr in recent photography trends, is that your final output is a capture that looks more real to your eye, and properly done has a mildly surreal look, as the photo has multiple exposures that capture the lighting just so.  The magic happens when you tonemap the image in the appropriate software, and the highlighted areas are combined into a final image.  Most good photography sites say "true HDR photography" cannot be culled from a single set of data or image.  Yes an .exr file- which I do understand to be an HDRI format, contains the infinite lighting possibilities, but to really make the image POP takes multiple captures, with contrasting areas of highlights and reflections.  Once these are combined the true nature (as implied by a photographer) is revealed in the final image.  One single .exr file tonemapped in Photomatrix (in my experience) is no where near the result of multiple images or exposures.  The same can be said from a photographers perspective.  A RAW file contains infinite possibility's, and yes a decent HDR can be produced from a single file.  To really achieve the desired effect though takes multiple exposures to get the lighting to pop at every level.  In my camera I shoot bracketed RAWs that give me three RAW image files at different exposures.  Some people take up to twenty.  If I tonemap one RAW file, I would never consider that a TRUE HDR photograph.  I feel the same holds true for .exr.  You can do it with one.   But try it with three or better yet six!   - Bill .
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Offline Oshyan

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Re: exposure times for HDR
« Reply #9 on: February 24, 2009, 03:40:03 AM »
Unfortunately that's not correct at all. The reason HDR from modern digital cameras requires multiple exposures is that the maximum sensor accuracy is currently *14 bit*. So even a RAW file from a camera has no more than 14 bits of color data per channel. EXR's from TG2 are fully 32 bit/channel, which is what you effectively achieve by combining multiple images from a camera at different exposures. The end result is a similar level of exposure range, but TG2 is able to natively produce it due to a highly accurate internal rendering system.

- Oshyan

Offline Cyber-Angel

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Re: exposure times for HDR
« Reply #10 on: February 24, 2009, 11:19:49 AM »
There are dedicated cameras, I understand, that are specifically designed for HDRI imagery, this would depend on the type of HDRI map that will result I am sure a Google search for "HDRI Camera" would though up some results.  ;D

Regards to you.

Cyber-Angel     

Offline matrix2003

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Re: exposure times for HDR
« Reply #11 on: February 24, 2009, 09:11:34 PM »
Thank you C-A, but I have enough gear right now.  Any more and I will get divorced!  ::)  (and you can do HDRI with any camera that has exposure settings)

My problem Osh is that I am thinking like an old photographer! (40 years of shooting)
My Terragen experience only goes back to 1997!  ;)

Since HDRI originated in 3D and just recently exploded into photography, all I have to go on here was my experience with a camera. I do have a handle on the whole 32 bit thing, and I guess I need to modify my technique then, and research how to do more editing at the 32 bit level, and forget my photo mentality!  Thank you for the explanation as I have done many HDR shots but never had it explained that way. I understand that the camera slams the door shall we say on many elements in a photo, but I guess I did not fully comprehend the extent.

See-  you can teach old dogs new tricks.   -  Bill .
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Offline Cyber-Angel

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Re: exposure times for HDR
« Reply #12 on: February 24, 2009, 11:44:37 PM »
Hi Matrix2003,

While what you say is true, I would find it areal pain dealing with all that exposure bracketing to get enough light data to form the HDRI prob. Also you have the problem that is faced in panoramic photography [Taken without a dedicated panoramic camera] and that is moving the camera in such away that the image will stitch together correctly latter, complicated enough without the additional complications of exposure bracketing.

There are added complications that I envisage with not using dedicated kit, the two that spring immediately to mind are shadow matching in the requisite number of exposures that are needed for a HDRI Probe image to be constructed; the other complication that is the bane of photographers the world over is keeping a clear frame for the whole shoot, we as you know live in a crowed world, people, traffic, birds and a whole raft of other frame clutter can and often dose wounder into frame when its lest opportune for that entity to do so, as a photographer myself all I can say is thanks but no thanks.

Any way by this round about route have a look at this camera http://www.artvps.com/page/112/hdrimaging.htm if you have not already done so could be just the thing [maybe]. ;D

Regards to you.

Cyber-Angel 

Offline rcallicotte

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Re: exposure times for HDR
« Reply #13 on: February 25, 2009, 12:42:05 AM »
Ben Wilmore has a DVD on HDRI and has some good tips on utilizing a camera and Photoshop to make cool images.  Not sure what this has to do with TG2, though, since we don't need to bracket TG2...I'm not sure it would even help to bracket TG2.
So this is Disney World.  Can we live here?

Offline matrix2003

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Re: exposure times for HDR
« Reply #14 on: March 07, 2009, 08:30:04 PM »
Well I have one last question, er issue,   - or I feel "I need a another explanation so that I can wrap my brain around this".

If a RAW image is 14 bit, and there are many web tutorials out there on producing HDR imagery from a single RAW image,
(GOOGLE: "HDR image from one raw image"   LINK: http://tiny.cc/txo2B)   AND an EXR file from T2 which is 32 bit file format,

...so with 32 bits of info, I can't use the same technique to post process an image like thousands do with 14 bits?  I know I'm being a pest, but that makes no sense to me at all!

 - Bill . 
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