Hi,
I wonder if it is possible to convert pictures taken by digital camera to Radiance format? And if yes, how it could be done? The Radiance format enables reading of luminance values directly from the pictures, something that could be very usefull in the project I plan to start soon.
Much appreciate any contribution.
Barbara.
Barbara,
Check out the pages on HDR imaging by Axel Jacob:
http://luminance.londonmet.ac.uk/webhdr/
-John
-----------------------------------------------
Dr. John Mardaljevic
Senior Research Fellow
Institute of Energy and Sustainable Development
De Montfort University
The Gateway
Leicester
LE1 9BH, UK
+44 (0) 116 257 7972
+44 (0) 116 257 7981 (fax)
Barbara Matusiak wrote:
I wonder if it is possible to convert pictures taken by digital camera to Radiance format? And if yes, how it could be done? The Radiance format enables reading of luminance values directly from the pictures, something that could be very usefull in the project I plan to start soon.
Yes, but only if you shoot the images in a specific manner and convert them to high dynamic range (HDR) format first. A single image does not contain the dynamic range necessary for what you want to do. But for typical scenes, if you simply bracket your exposure (using aperture, not changing shutter speed) by two F stops in each direction, you can use utilities like Debevec's HDR Shop or Greg Ward's Photosphere (or his command-line hdrgen) to merge those into an HDR image with the full dynamic range. You can then use Radiance tools like falsecolor (and even pcond) to extract real luminance information from a photograph.
We use a Canon Digital Rebel here in my office to create these image sequences. The autobracket function of the camera is very useful for this. Many "prosumer" cameras have this feature, but you must make sure the camera will separate the images by two f-stops. Of course you can do it manually too, but then you usually need a tripod to keep everything in registration. You also need to "go manual" to capture scenes of really high dynamic range, using more images to capture the full range.
I've been meaning to place some samples on my website, but haven't had time. But these resources are better anyway:
http://www.anyhere.com/
http://www.debevec.org/HDRShop/
HDR photography is extremely cool. You can even use HDR images as light sources for Radiance scenes! Santiago Torres of this list has done quite a bit of work in that. Search the radiance-general archives for details. Have fun!
Hi Barbara,
Mentioned on Axel Jacob's webpage (http://luminance.londonmet.ac.uk/webhdr/ as noted by Dr. M) is my application called Photosphere that enables one to manage and assemble HDR images from multiple exposures. To facilitate camera-based photometric work, I have recently added a calibration feature to obtain more accurate absolute luminances from the resulting HDR images. Photosphere currently works only under Mac OS X, though I've been searching around for someone with sufficient talent and free time to port it to Windoze. Photosphere (and the command-line version "hdrgen") may be found at my personal website:
Output to Radiance as well as LogLuv and floating-point TIFF, and now OpenEXR formats are supported. If you want some examples of HDR images, check out Erik Reinhard's website as well:
http://www.cs.utah.edu/~reinhard/cdrom/hdr.html
I have a whole slew of HDR images I've created with Photosphere, but have not found a place to put them on the web as yet.
-Greg
P.S. Say "hej" to Oyvind for me!
From: Barbara Matusiak <[email protected]>
Date: May 28, 2004 6:24:40 AM PDTHi,
I wonder if it is possible to convert pictures taken by digital camera to Radiance format? And if yes, how it could be done? The Radiance format enables reading of luminance values directly from the pictures, something that could be very usefull in the project I plan to start soon.
Much appreciate any contribution.
Barbara.
A minor correction to Rob's note -- you should actually fix the f-stop and vary only the shutter speed in your exposures, not the other way around. The reason for this is that f-stops are not very reliable or repeatable on most cameras, but shutter speed is reasonably sure. Here is an excerpt from the quickstart_pf.txt file that comes with Photosphere:
To create a high dynamic-range image, you need to start with
a set of "bracketed" exposures of a static scene. It is best if
you take a series of 10 or so exposures of an interior scene looking
out a window and containing some large, smooth gradients both inside
and outside, to determine the camera's natural response function.
Be sure to fix the camera white balance so it doesn't change, and
use aperture-priority or manual exposure mode to ensure that only
the speed is changing from one exposure to the next. For calibration,
you should place your camera on a tripod. Take your exposure series
starting from the longest shutter time and working to the shortest in
one-stop increments. Make sure the longest exposure is not all white
and the darkest exposure is not all black. Once you have created your
image series, load it into Photosphere directly -- DO NOT PROCESS THE
IMAGES WITH PHOTOSHOP or any other program. Select the thumbnails,
then go to the "File -> Make HDR..." menu. Check the box that says
"Save New Response", and click "OK". The HDR building process
should take a few minutes, and Photosphere will record the computed
response function for your camera into its preferences file, which
will save time and the risk of error in subsequent HDR images.
You will also have the option of setting an absolute calibration
for the camera if you have a measured luminance value in the scene.
This option is provided by the "Apply" button submenu when the
measured area is selected in the image. (Click and drag to select.)
Once an HDR image has been computed, it is stored as a temporary
file in 96-bit floating-point TIFF format. This file is quite
large, but the data will only be saved in this format if you
select maximum quality and save as TIFF. Otherwise, the 32-bit
LogLuv TIFF format will be preferred (or the 24-bit LogLuv format
if you set quality to minimum). You also have the option of saving
to the more common Radiance file format (a.k.a. HDR format), or
ILM's 48-bit OpenEXR format. If you choose not to save the
image in high dynamic-range, the tone-mapped display image can be
written out as a 24-bit TIFF or JPEG image.
-Greg
Greg Ward wrote:
A minor correction to Rob's note -- you should actually fix the f-stop and vary only the shutter speed in your exposures, not the other way around.
Oops, that's what I meant. I hereby solemnly swear to never again post anything to the Radiance list without first having had a cup of coffee.
Aperture priority, baby!
-RPG
Greg Ward wrote:
A minor correction to Rob's note -- you should actually fix the f-stop and vary only the shutter speed in your exposures, not the other way around. The reason for this is that f-stops are not very reliable or repeatable on most cameras, but shutter speed is reasonably sure. Here is an excerpt from the quickstart_pf.txt file that comes with Photosphere:
Another more fundamental reason is that f-stops affect depth of field and therefore the effect of focusing errors and lens aberrations. If you vary the aperture, your images may not be consisent in focus, particularly in near field photography. This course assumes the digicam implement f-stops traditionally with an actual diaphragm. If it simply modulates the CCD gain (as I believe most El Cheapo digicams tend to do) this is all moot anyway.
--
Roland Schregle
PhD candidate, Fraunhofer Institute for Solar Energy Systems
RADIANCE Photon Map page: www.ise.fhg.de/radiance/photon-map
END OF LINE. (MCP)
Hi Barbara,
I don't recommend using the RAW format for Photosphere or hdrgen. Since there is no "RAW" standard -- RAW is a maker-specific and model-specific(!) format, conversion is necessary before it can be read by any other program (with few exceptions). You only complicate your life by using RAW, and some of the exposure information that Photosphere and hdrgen need is usually lost in translation to JPEG or TIFF.
I'm sorry the manual page for hdrgen is missing from the binaries that are currently on the anyhere site -- I'll have to fix that as soon as I'm able to get back on there. (They upgraded their servers and ssh isn't working right now.) I am attaching the HTML documentation for hdrgen for your convenience.
If you can gain access to a Mac running OS X, you'll find it much easier to create and calibrate HDR images with Photosphere, I bet.
-Greg
hdrgen.html (12.1 KB)