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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 -- For email replies, please substitute the obvious. |
#2
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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
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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 -- For email replies, please substitute the obvious. |
#4
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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. |
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Measurung dynamic range...
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#7
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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 |
#8
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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 |
#9
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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 |
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