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Measurung dynamic range...



 
 
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  #1  
Old August 4th 06, 03:03 PM posted to rec.photo.digital
Volker Hetzer
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Posts: 79
Default Measurung dynamic range...

Hi!
I'd like to measure the dynamic range of my digicam.
How would I go about it?
Are there special targets for this?

Lots of Greetings!
Volker
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  #2  
Old August 4th 06, 04:08 PM posted to rec.photo.digital
Bart van der Wolf
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Posts: 314
Default Measurung dynamic range...


"Volker Hetzer" wrote in message
...
Hi!
I'd like to measure the dynamic range of my digicam.
How would I go about it?
Are there special targets for this?


The T4110 is ideal for the purpose:
http://www.stouffer.net/TransPage.htm#transmission%20step

For evaluation you can either device your own tool for free, e.g. by
using ImageJ:
http://rsb.info.nih.gov/ij/
or use a much easier setup like Imatest;
http://www.imatest.com/docs/tour_q13.html
but it may be a bit expensive if you need it for more than the free
number of evaluations and only want to check DR on a single camera.

The Imatest site has a lot of useful info and links, so I suggest to
absorb as much as possible, and then choose the approach you seem fit.
Whatever avenue you choose, the T4110 is a must if you want to get
anywhere with a single exposure DR analysis.

If you want to try multiple exposure shots of a uniform
(structure+lighting) surface, or just want to absorb even more
relevant data, you can read about Roger Clark's findings:
http://www.clarkvision.com/imagedetail/digital.signal.to.noise/ .

--
Bart

  #3  
Old August 5th 06, 06:00 PM posted to rec.photo.digital
Volker Hetzer
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Posts: 79
Default Measurung dynamic range...

Bart van der Wolf schrieb:

"Volker Hetzer" wrote in message
...
Hi!
I'd like to measure the dynamic range of my digicam.
How would I go about it?
Are there special targets for this?


The T4110 is ideal for the purpose:
http://www.stouffer.net/TransPage.htm#transmission%20step

I have contacted them and will have a look at the other links you provided.

Thanks a lot for helping!
Volker

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  #4  
Old August 6th 06, 02:34 PM posted to rec.photo.digital
[email protected]
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Posts: 51
Default Measurung dynamic range...


Volker Hetzer wrote:
Hi!
I'd like to measure the dynamic range of my digicam.
How would I go about it?
Are there special targets for this?

Lots of Greetings!
Volker
--
For email replies, please substitute the obvious.


Really measuring dynamic range is quite a difficult job. Part of the
problem is that there are two different definitions of dynamic range.
A second is that one must have a camera and software to use RAW file
format.

One quick and dirty test is to shoot a pic with lens cap on.

Using a photo editor, poke around and sample what appears to be lighter
areas- noise. Take a bunch of pixel brightness values (using color
picker). Average these values by squaring each value and summing, then
take square root of total. This will give you the noise level.

  #5  
Old August 7th 06, 02:44 PM posted to rec.photo.digital
[email protected]
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Posts: 51
Default Measurung dynamic range...


wrote:


Really measuring dynamic range is quite a difficult job.


In reading my post I see I really left out a lot, and didn't explain
myself very well. The problem is accurate radiometry/photometry.
Accurately measuring light is not a trivial problem- the instruments
are expensive and need frequent calibration. The big problem is
getting black references. White references are easy to do, and don't
need super accuracy. The problem is, what is the brightness, or even
reflectivity of a black reference.

To simplify the math, lets look at Black and White, say an 8 bit grey
scale. There can be up to 256 values in the image. But the best
available black inks or paints have a reflectivity of about 2-3%. If
we use a single even illumination, then a black and white printed chart
has a dynamic range of 50:1 or less. Thus, we can't use a printed
chart to test a camera with a dynamic range of 250:1 or 500:1.

I am working on a low cost "light trap" using a pringles can and
self-adhesive black felt. If this works out I intend to write an
article on it for a camera magazine, along with some stuff on measuring
dynamic range and flare performance. I intend to use this first on my
scanner, but will use it for some tests on my cameras too.

  #6  
Old August 7th 06, 03:41 PM posted to rec.photo.digital
Volker Hetzer
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Posts: 79
Default Measurung dynamic range...

Roger N. Clark (change username to rnclark) wrote:

A good way to make a light trap is a cone painted with
glossy black paint. The reflections from the painted surface
go deeper into the cone.

So the camera looks into the pointy end?
Otherwise it seems to me that the light gets reflected back.

Lots of Greetings!
Volker
  #7  
Old August 7th 06, 03:44 PM posted to rec.photo.digital
Volker Hetzer
external usenet poster
 
Posts: 79
Default Measurung dynamic range...

wrote:
wrote:

Really measuring dynamic range is quite a difficult job.


In reading my post I see I really left out a lot, and didn't explain
myself very well. The problem is accurate radiometry/photometry.
Accurately measuring light is not a trivial problem- the instruments
are expensive and need frequent calibration. The big problem is
getting black references. White references are easy to do, and don't
need super accuracy. The problem is, what is the brightness, or even
reflectivity of a black reference.

I've got a light trap from basiccolor, so that's not much of a problem
for me. (Can't recommend it though, for EUR70 you get some cheap wood
and plastic stuff.)


To simplify the math, lets look at Black and White, say an 8 bit grey
scale. There can be up to 256 values in the image. But the best
available black inks or paints have a reflectivity of about 2-3%. If
we use a single even illumination, then a black and white printed chart
has a dynamic range of 50:1 or less. Thus, we can't use a printed
chart to test a camera with a dynamic range of 250:1 or 500:1.

I can do that by putting the stuff against a window in a darkened room or
even a box. Not sure yet.
What I will probably need is a large translucent grey slide too,
to embed the wedge in it and check different exposure settings like
center weighted or matrix or generally measuring exposure against the grey
and then compensating to get maximum range.

Lots of Greetings!
Volker
  #8  
Old August 7th 06, 04:20 PM posted to rec.photo.digital
Roger N. Clark (change username to rnclark)
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Posts: 1,818
Default Measurung dynamic range...

wrote:

wrote:


Really measuring dynamic range is quite a difficult job.



In reading my post I see I really left out a lot, and didn't explain
myself very well. The problem is accurate radiometry/photometry.
Accurately measuring light is not a trivial problem- the instruments
are expensive and need frequent calibration. The big problem is
getting black references. White references are easy to do, and don't
need super accuracy. The problem is, what is the brightness, or even
reflectivity of a black reference.

To simplify the math, lets look at Black and White, say an 8 bit grey
scale. There can be up to 256 values in the image. But the best
available black inks or paints have a reflectivity of about 2-3%. If
we use a single even illumination, then a black and white printed chart
has a dynamic range of 50:1 or less. Thus, we can't use a printed
chart to test a camera with a dynamic range of 250:1 or 500:1.

I am working on a low cost "light trap" using a pringles can and
self-adhesive black felt. If this works out I intend to write an
article on it for a camera magazine, along with some stuff on measuring
dynamic range and flare performance. I intend to use this first on my
scanner, but will use it for some tests on my cameras too.

Procedures for Evaluating Digital Camera
Sensor Noise, Dynamic Range, and Full Well Capacities
http://www.clarkvision.com/imagedetail/evaluation-1d2

Gets around these problems, but you need access to the raw
data. Other tests typically use transmission targets.

A good way to make a light trap is a cone painted with
glossy black paint. The reflections from the painted surface
go deeper into the cone. At the bottom of the cone, have
a deep hole ~1mm diameter. A long pipe also works, as in
Figure 1, 2 at:

Dynamic Range and Transfer Functions of Digital Images
and Comparison to Film
http://www.clarkvision.com/imagedetail/dynamicrange2

Roger
  #9  
Old August 7th 06, 08:27 PM posted to rec.photo.digital
Roger N. Clark (change username to rnclark)
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Posts: 1,818
Default Measurung dynamic range...

Volker Hetzer wrote:
Roger N. Clark (change username to rnclark) wrote:

A good way to make a light trap is a cone painted with
glossy black paint. The reflections from the painted surface
go deeper into the cone.


So the camera looks into the pointy end?
Otherwise it seems to me that the light gets reflected back.


Yes. Think of an ice-cream cone. Look at the inside,
and paint it glossy black. A machined metal (like aluminum)
works very well.

Roger
  #10  
Old August 7th 06, 08:32 PM posted to rec.photo.digital
Bill Funk
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Posts: 2,500
Default Measurung dynamic range...

On Mon, 07 Aug 2006 12:27:11 -0700, "Roger N. Clark (change username
to rnclark)" wrote:

Volker Hetzer wrote:
Roger N. Clark (change username to rnclark) wrote:

A good way to make a light trap is a cone painted with
glossy black paint. The reflections from the painted surface
go deeper into the cone.


So the camera looks into the pointy end?
Otherwise it seems to me that the light gets reflected back.


Yes. Think of an ice-cream cone. Look at the inside,
and paint it glossy black. A machined metal (like aluminum)
works very well.

Roger


Wouldn't machined (or even moreso, polished) metal reflect much more
light?
Why did you pick glossy black?
--
Bill Funk
replace "g" with "a"
 




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