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Samus
06-01-2010, 04:44 AM
Hi ,

i've been trying to make my on HDRI, somehow when merged in
HDR shop, photoshop or Photomatix i get a low quality HDR witch
does not generate good lighting. Would any Hdr Guru's help me
with any tips.

thank's

rsfd
06-01-2010, 06:28 AM
...i get a low quality HDR...
in what terms? is it just too dark, or do you get color issues or noise?
Do you create at least 2 HDR images (low resolution+blurred for GI and high res+sharp for reflection), or do you use high res HDRIs with low GI sample settings and are ending up in noisy renders?

What range do you cover when shooting your bracketed images? (3 img in 1EV steps e.g. is far too little).

Are you using RAW files to generate your HDRI? (it's better than using .jpg or .tif)

What are your output settings? (I would recommend OpenExr as file type).

Are you balancing the exposure in photoshop after having generated the HDRI in e.g. Photomatix? (to achieve a certain level of luminosity as base value).

If you don't know it already, have a look at hdri labs website.
They also offer some tutorials (http://www.hdrlabs.com/tutorials/index.html).

(hopefully this is somewhat helpful)

Samus
06-01-2010, 07:17 AM
my photos are made with a conventionnal camera no DSLR,
however i do many different exposures, the least is three images.
no bracketed options on my small Olympus x-875.

I merge a series of JPG (LDR images). my outputs are HDR or TIFF.

cheers

rsfd
06-01-2010, 08:24 AM
my photos are made with a conventionnal camera no DSLR...
but digital anyway i guess
(when on film, the creation of HDRI is extremely painful because of the scanning process)


...however i do many different exposures, the least is three images...
how many images you have to take depends on the existing contrast range when shooting the HDRI. The higher the contrast, the more exposures are needed to capture this contrast.
On contrasty scenes (in full sun), you will end up with at least 6 exposures in 2 EV steps (or 12-14 images in 1 EV steps).
In diffuse light situations, 4-6 exposures in 2 EV steps are usually enough.


no bracketed options on my small Olympus x-875.
well, that's only a comfort feature, most pro DSLR don't offer enough brackets to shoot the needed exposures in one turn either. As long as you can set up the exposure manually and shoot the row by changing only the exposure time (never change the aperture), you are all set.


I merge a series of JPG (LDR images). my outputs are HDR or TIFF.
OpenEXR is really worth a look, but .hdr or .tif do work too (as long as it's 32-bit linear color space).

Samus
06-01-2010, 11:10 AM
Ill try OpenExr. Thanks for the tips "rsfd" keep em' coming if you got more.

Thanks.

inakito
06-02-2010, 03:00 AM
I think u wont bew able to create a hdri unless u shot raw files or something similar... so i dont think jpgs will do the work

bjornkn
06-02-2010, 03:42 AM
Jpg works just fine for HDR. IMO it is overkill to shoot RAW for merging to HDRs. I have made HDR spherical panoramas from both RAW and JPG, and there is no difference between them.
To be used successfully for IBL they should have a lot of bracketed shots. I usually make 2EV steps from almost pure white to pure black, 7 - 9 brackets. HDR or EXR for file format works fine in LW.
If you don't use it already, check out sIBL.
It works great :)

rsfd
06-02-2010, 03:47 AM
well, answering questions is a lot easier than writing an article :)

I had a quick look at the tech specs of your camera and as far as I can tell it unfortunately does not allow to manually set up the exposure values.
It only allows automatic modes and an exposure correction (don't know the enabled range, but could be too small e.g. 1EV).

Honestly, that isn't appropriate for correct HDR image creation, as you have to use a constant aperture for the whole range and only change the exposure time.

And that isn't possible with automatic settings, even exposure correction doesn't give you control over what is changed: the camera electronic decides if it changes exp.-time or aperture to achieve the wanted correction.
Also, changing the ISO setting to create the exposure row (doubled ISO value = 1 EV) results in different combinations of time/aperture and with higher ISO you will most likely run into noise issues.

As you are shooting jpg, remember to set the White Balance to a fixed value (e.g. "sun" or "shadow"), so that at least the colors don't change too much.

Sorry, I hope that wasn't too disappointing!

You could download some example hdr sets on the Hdrlabs website and compare how they look and work when used for radiosity.
You'll find them on the SmartIBL Archive page (http://www.hdrlabs.com/sibl/archive.html).
The sets usally consist of 3 HDR images: one low res / blurred for environment (GI), one mid res for reflections (when using the sIBL script, this image is mapped onto a ball which surrounds the whole scene) and a high res image as background (used also on a ball geometry when the background should be rendered).

[edit]
addition:
jpg vs. RAW
jpg can be used of course, but RAW gives: higher dynamic range data, higher color data (jpg is 8-bit, RAW usually between 12-16 bit, depending on the used camera) and a linear gamma.
jpg contain a gamma applied through the camera electronic whereas RAW files are already in linear color space, so if you use a software which allows for merging RAW files, this typically results in better quality HDRI.
HDR software takes the gamma out of jpg, but this isn't as exact as the direct use of RAW data.