[Radiance-general] Problems using hdrgen for hdri generation

[Giulio Antonutto]

Hi,
here something:
 
-1- you need to change time and NOT aperture, since depth of field changes
with aperture settings.
(depth of field could be simply explained as the parameter that indicates
how we are able to see more things in focus other than just the foreground)
furthermore close apertures eliminate some lens artefacts like coma (light
sources are elongated when close to the frame of the picture, expensive
lenses have not this problem though)...  
as a general suggestion for luminance measurement I would recommend to use
big F numbers.
 
-2- aperture=F stop=F number   <> time, exposure time,shutter speed
 
basically there is a curtain inside the camera that moves:
this is the shutter and takes care of let in the light
(speed is indicated in seconds and fraction of seconds, 1/60 is 1/60 of
second sometimes it is written as 60)
 
there is a diaphragm inside lenses,
this close  when the picture is being taken, leaving just an hole in the
middle, the hole dimension is the aperture.
the smaller the hole the bigger is aperture number (it's a fraction 1/1.4
1/2 1/2.8 .... 1/16 1/22 1/32 ... 1/64)
the smaller the hole the bigger depth of field
 
 
 
-3a- 'trouble about HDR patches' doesn't seem to be a problem, it is a
warning and results are always fine... sounds like 'warning no light source
found' and you are calculating a DF... ;-))
 
-3b- this happens when images have not enough data to create the camera
calibration curves... 
may be others can explain in depth....
 
-4- this could be because the images are too different or some exif data are
missing (sometimes this happens because the software that imports images
overwrite exif data)
 
-5- no idea
 
-6- I found the same thing, however a good tripod 'fixed' all my problems
;-))
 
Hope it helps,
cheers,
pillo
 
 


 
 -----Original Message-----
From: radiance-general-bounces at radiance-online.org
[mailto:radiance-general-bounces at radiance-online.org]On Behalf Of Despina
Michael
Sent: 06 January 2005 17:08
To: radiance-general at radiance-online.org
Subject: [Radiance-general] Problems using hdrgen for hdri generation


Hi all,
 
I am a student and I am new to hdri generation or processing so I need your
help:)
 
I am trying to use hdrgen (for linux) for generating an hdr image from a
series of photographs with different exposure each, of a static scene . 
I faced some problems and I have some questions for the whole process..
 
1) First of all, I would like to know which is the best way to take
photographs with different exposure. 
If I understand correctly there are two ways. Either by changing F-number
and let fixed the shutter speed or either by varying shutter speed and let
the f-number fixed.
I would like to know witch of two ways is the best?
 
2) Are "Lens Aperture", "F-number" and "F-stop" same thing? 
Are "exposure time" and "shutter speed" same thing?
I know that these questions may seem to be "stupid" to most of you.. but as
I said I am not familiar at all, with all these ..
 
 
The following questions are for hdrgen software..
I used it with different combinations of image... 
Some times the hdr image is generated but it's not clear at all and "scene"
are not aligned... and some other times the hdr image is not generated at
all..
 
3) Where is the fault 
when there is a warning:  Trouble finding HDR patches***** ?
when ther is a warning: Poor convergence for order 1 fit? (is 1 or any other
number X appear there refers to a problem with the Xth image in command
arguments?)
 
4) Where is the fault when there is an error:
"Cannot solve for response function" ?
Is that because it can not generate file for response function of camera,
with specific series of photographs?
 
5) One problem of resulting hdr images (in cases that there was a generation
of image)
was that they were somehow "green". What can cause that?
 
6) My photographs are not perfectly aligned. 
As I understood, the hdrgen uses an algorithm to align the photographs.
But as I noticed when the uses of alighnment algorithm is enable (NOT use of
-a option) the "alignment" getting worst..
and when I disabled it (Using -a option) the result is better.. but still no
good (I guess because that original photographs are not aligned)
 
Is there anything I can do for that???
Does the algorithm has "limits" on how much dis-aligned can the original
images be?
 
I would appreciate it if you can answer some (or all;-)  ), of these
questions.
Regards,
Despina
 


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