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General => Terragen Discussion => Topic started by: ravex on February 21, 2009, 02:02:21 PM

Title: exposure times for HDR
Post by: ravex on February 21, 2009, 02:02:21 PM
Hi guys.
i want just ask. how in render or camera get multiple exposure times for build HDR Image like This
(http://www.multimediaphoto.com/images/grandcanal/grandcanal_tm400.jpg)
this sample created from 3 different exposure times
1/750, 1/180 and 1/45s.
(http://www.multimediaphoto.com/images/grandcanal/grandcanal_under120.jpg)
(http://www.multimediaphoto.com/images/grandcanal/grandcanal_mean120.jpg)
(http://www.multimediaphoto.com/images/grandcanal/grandcanal_over120.jpg)

how get this image effect in TG2?
Title: Re: exposure times for HDR
Post by: matrix2003 on February 21, 2009, 02:37:13 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 .
Title: Re: exposure times for HDR
Post by: PorcupineFloyd on February 21, 2009, 02:43:14 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.
Title: Re: exposure times for HDR
Post by: Oshyan on February 21, 2009, 03:26:36 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
Title: Re: exposure times for HDR
Post by: matrix2003 on February 21, 2009, 05:30:34 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 . 
Title: Re: exposure times for HDR
Post by: mt_sabao on February 21, 2009, 08:49:54 PM
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.
Title: Re: exposure times for HDR
Post by: matrix2003 on February 21, 2009, 09:10:26 PM
.EXR into Photomatrix.
Title: Re: exposure times for HDR
Post by: rcallicotte on February 21, 2009, 11:08:24 PM
.EXR in Photomatix.  Right.
Title: Re: exposure times for HDR
Post by: matrix2003 on February 23, 2009, 04:39:50 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 .
Title: Re: exposure times for HDR
Post by: Oshyan on February 23, 2009, 11:40:03 PM
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
Title: Re: exposure times for HDR
Post by: Cyber-Angel on February 24, 2009, 07:19:49 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     
Title: Re: exposure times for HDR
Post by: matrix2003 on February 24, 2009, 05:11:34 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 .
Title: Re: exposure times for HDR
Post by: Cyber-Angel on February 24, 2009, 07:44:37 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 
Title: Re: exposure times for HDR
Post by: rcallicotte on February 24, 2009, 08:42:05 PM
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.
Title: Re: exposure times for HDR
Post by: matrix2003 on March 07, 2009, 04:30:04 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 . 
Title: Re: exposure times for HDR
Post by: jo on March 07, 2009, 06:59:45 PM
Hi Bill,

Well, in this tutorial:

http://www.aguntherphotography.com/tutorials/raw-hdr-processing.html

He's just using the combination of several 14 bit images to make one 32 bit image. With TG2 images you don't need to bother with that. Just do the tonemapping to get the effect you want.

However I'm sure some of the effects people get from processed HDR images also come from the way they combine the lower dynamic range images into the single image. I would imagine that the process doesn't give as "pure" a 32 bit image as TG2. You can always experiment with saving TG2 images generated by TG2 with different exposure settings and then combining them if you feel like it. Strictly speaking there is no need, but you may find you can process them in such a way as to give a particular result.

BTW, anything over 8 bit is an HDR ( high dynamic range ) image really. A 14 bit RAW image from a camera is already HDR, it has a far greater dynamic range than an 8 bit JPEG from a camera.

Regards,

Jo


Title: Re: exposure times for HDR
Post by: Mohawk20 on March 07, 2009, 07:27:03 PM
So basically what they're saying is that you can use the exr output to get several exposures from one render and combine them to a hdri image that is to your liking.
But you don't have to use a time consuming method (though you probably do it very easily), since all the info is allreasy in teh exr, so if you tweak the single image in a program like PhotoMatix (or even PhotoShop), you might get the same results, or even better.


One difference I noticed was when increasing exposure settings in photoshop. A normal bmp output of a transparent blue rock on a black background will have the black background go gray when increasing the settings. The exr however kept the background black, while the internals of the rock showed up really good.

If you want, you should really try it out, but you can still use your 'old' method if that works for you.
Title: Re: exposure times for HDR
Post by: matrix2003 on March 09, 2009, 05:58:28 PM
Thanks Jo and Mohawk.
"The devil is in the detail"

... I guess my point was, the technique if used properly has some interesting results.
The way you postwork the images definitely can dramatically change the output,
beyond the capabilities of strictly processing EXR images in photomatrix or photoshop.

So my best advice should have been: Save all renders in the .EXR format, and post process any way you are comfortable with.  ;D
Title: Re: exposure times for HDR
Post by: gregsandor on March 09, 2009, 10:39:38 PM
To expand upon Jo's comment about the difference between TG's one-shot HDR production vs real-world, you could use TG and very slightly change the sun angle, cloud position, light intensity, etc. then combine the renders.  This will go a step toward recreating the natural variation in hand photographed HDR images.
Title: Re: exposure times for HDR
Post by: rcallicotte on March 09, 2009, 11:00:03 PM
Hey, that's an interesting possibility.  I'll try it!

Quote from: gregsandor on March 09, 2009, 10:39:38 PM
To expand upon Jo's comment about the difference between TG's one-shot HDR production vs real-world, you could use TG and very slightly change the sun angle, cloud position, light intensity, etc. then combine the renders.  This will go a step toward recreating the natural variation in hand photographed HDR images.
Title: Re: exposure times for HDR
Post by: matrix2003 on March 10, 2009, 07:17:01 PM
@gregsandor  There you go!  Three images with slightly different hues of cloud color.  Say pink, salmon and orange for a sunset.
Three with whacky numbers you would never use.  Three with crazy post work or -or three or more all rendered in T2, slightly modified.

I was suggesting  'think outside the box', when I said that I tweak the individual files vs. tone mapping a single image.
Push the envelope:  "To attempt to extend the current limits of performance. To innovate, or go beyond commonly accepted boundaries."   ::)

LOL   - Bill .
Title: Re: exposure times for HDR
Post by: Marcos Silveira on March 13, 2009, 11:21:08 AM
What is special about HDR images, I think they're horribly fake!!! Could someone send a link to some examples to make me change my mind?!?
Title: Re: exposure times for HDR
Post by: rcallicotte on March 13, 2009, 11:48:44 AM
@ro-nin -

http://forums.cgsociety.org/showthread.php?f=132&t=741150
http://forums.cgsociety.org/showthread.php?f=132&t=323956&highlight=HDR+lighting
http://forums.cgsociety.org/showthread.php?f=132&t=247258&highlight=HDR+lighting
http://features.cgsociety.org/newgallerycrits/g04/47404/47404_1236127067_large.jpg

The first and last are definitely using HDR, though I'm not sure what the second and third did to utilize HDR.
Title: Re: exposure times for HDR
Post by: Confusoid on March 13, 2009, 11:54:56 AM
Also using HDRI for not only lighting but shading will do wonders. Pixar's Wall-E used quite a bit of HDR to realistically render out metal and plastic surfaces for several of there models.
Title: Re: exposure times for HDR
Post by: Saurav on March 13, 2009, 05:54:53 PM
Quote from: ro-nin on March 13, 2009, 11:21:08 AM
What is special about HDR images, I think they're horribly fake!!! Could someone send a link to some examples to make me change my mind?!?

I shot this photo in Nepal a few months ago. 3 exposure of (+2, 0, -2) photos -> HDR -> tonemapped in photomatix. If you tried to shoot LDR or even shoot in RAW the highlights (snow) would blow out and you would loose a lot of details in the scene. HDR has it's place in photography, it can definitely be made to look natural. It's just that most people don't choose to process it that way because they like the 'fake' look. Personally I like the natural looking HDR photos more.
Title: Re: exposure times for HDR
Post by: rcallicotte on March 13, 2009, 11:12:36 PM
Beautiful photo, Saurav.
Title: Re: exposure times for HDR
Post by: Libra on November 05, 2017, 10:45:02 AM
In this article you'll find some tips on exposure value needed to create HDR photography  https://aurorahdr.com/what-is-hdr-photography (https://aurorahdr.com/what-is-hdr-photography).

(https://macphunsoftware.cachefly.net/upload/auroraLandings/5shotbracket11x.jpg)