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technique (Read 5361 times)
perycomo
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technique
08/22/07 at 17:40:12
 
"If you read The Handbook, you are certainly well aware that none of these actually is a high dynamic range image. They are all tone mapped down to LDR, in a variety of artistic styles."
Could someone explain what this means?
I thought they were (flicka HDR Gallery)all HDR and tone mapped.
Thanks in advance
Perry
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Blochi
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Hollywood
Re: technique
Reply #1 - 08/22/07 at 20:17:07
 
Well, this site is in fact a bit premature - it will all become clear when my book is out, bacause that should give the total insight on what High Dynamic Range really is and what not.

To cut a long story short: Images on Flickr are all JPEGs, right? Real HDR images cannot be represented in this file format, and the conversion process (called tone mapping) bakes them into Low Dynamic Range images. It might be true, that most of the Flickr images *have been* HDR images at some point, but so have a lot of them been RAW images, and yet they are not called that way on Flick anymore....

Here is a visual clue about the difference: 2 panoramas of the same image.

First one is true HDR. Pan around with your mouse and watch how you can change exposure however you want. All the data is still there.

[pano e=1300 g=1.4 ]http://www.hdrlabs.com/PanoGallery/media/Footprint_Court_3k.fjpg[/pano]

And this is a tonemapped version. Note that exposure is fixed, every pixel has a defined screen color. The challenge in tone mapping is to make the most out of HDR image, and get a nice looking LDR representation thereof.



Hope this clears it up a bit.

Blochi
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upshot
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Re: technique
Reply #2 - 08/22/07 at 20:44:09
 
Is that QTVR generated with photomatix hdr vr?  I still don't quite understand the workflow of that technique...
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Blochi
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Hollywood
Re: technique
Reply #3 - 08/22/07 at 22:19:09
 
And I don't really understand the question.

This was just to show the diffference between real HDR imagery and LDR images done via tonmapping an HDR down.

I see now, this was actually a bad example set. Here is a better one:

HDR panorama
[pano e=600 g=1.5 ]http://www.hdrlabs.com/PanoGallery/media/Ditch2-River_3k.fjpg[/pano]

and the LDR pano


There are way more examples in the Gallery section...
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upshot
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Re: technique
Reply #4 - 08/23/07 at 16:20:04
 
I'm just inquiring on the basic workflow that results in an HDR QTVR like your examples... ie:

a. take a series of bracketed shots in a sphere pattern with overlap
b. generate the HDR files out of the brackets(?)
c. stitch together with 'xyz' software
d. generate 'abc' file type with 'qrs' software
e. place 'abc' file in website with ptviewer

I'm just not familiar with the workflow of that technique...
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Blochi
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Re: technique
Reply #5 - 08/23/07 at 18:06:59
 
Grrr .... just wrote a long answer, then slipped on the keyboard and it reloaded the page. All gone.


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Blochi
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Re: technique
Reply #6 - 08/23/07 at 18:32:55
 
So here we go again:

Well, this is actually a huge topic. Bernhard Vogl wrote an excellent tutorial on this subject in the HDRI Handbook. Very elaborate and detailed, with practical shooting tips and problem solving for the stitching part. However, since the book is not quite out yet, here is the quick rundown of my favorite workflow:

1. Shoot the same brackets in each direction, with 20%-25% overlap.
2. Load them all into PTgui Pro. This app can merge HDRs and stitch panos in one step.
3. For the web, make it not bigger than 3200x1600 pixels, and save as Radiance .hdr.
4. Convert it to .fjpg with PTConvert.
5. Attach the .fjpg to your post or upload it to your own server.
6. To display it with the inline PTViewer, place this tag in your post:
Code:
[pano e=500 g=1.6 ]http://www.hdrlabs.com/yabbfiles/Attachments/YOURFILENAME.fjpg[/pano]
 



Note the path, that will always be like this - except for your file name. The parameters in the [pano] tag are:
e ... default exposure. Try 300 up to 1000
g ... display gamma. Lower values result in more contrast... try 1.4 to 1.8

Oh, and VERY IMPORTANT - There must be a space between the gamma value and the closing bracket of the [pano] tag. Otherwise it won't work.

There is also a free alternative to PTGui Pro, but it's more work and slightly less accurate...

2a. Use Picturenaut or your favorite utility from the Tools page to merge each sector into an HDRI.
2b. Save them in a separate folder as Radiance .hdr
2c. Stitch the original middle exposures in Hugin, save the project file next to originals and quit.
2d. Move the projectfile manually to the folder with the HDR images.
2e. Open it back up in Hugin, and point it to the HDR files.
2f. Now just run the stitcher, and save your final pano as floating point TIFF.
2e. Convert it to .HDR and delete the ridiculously huge FP TIFF file.

Cheers,
Blochi

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upshot
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Re: technique
Reply #7 - 08/23/07 at 19:01:10
 
Very cool! Thanks... First time I've been exposed to PTGui... I've been a fan of panorama shooting for a long time now. I'll have to give it a spin!
...
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Blochi
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Hollywood
Re: technique
Reply #8 - 08/23/07 at 20:18:28
 
Sweet. Times Square, if I'm not mistaken... Just happened to be there as well, timelapsing away:



Oh, and sorry, I forgot: The [pano] tag only works when the image was attached to the post. That's a stupid limitation of PTViewer, it can only show images that are on the same server....  

Blochi
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