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Re: image density, log exposure (-target density) and pixel level

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On 1/26/2019 4:19 PM, dale wrote:
> On 1/26/2019 3:34 AM, imran.kanjoo@gmail.com wrote:
>> Hello, every body. I want to find the pixel level of the image. The 
>> image contains 6 gray scale squares with different intensity in each 
>> patch. I know the pixel level is given by
>>
>> pixel level = 255 * (10–density/1.01)(1/2.2)
>>
>> but I do not know how to find out the density. Finally I need to have 
>> a graph pixel level vs log exposure (-target density). Can any body 
>> also explain how can I find the log exposure (-target density). Thank 
>> you.
>>
> 
> The pixel level you described (exposure) is an approximation of a gamma 
> 2.2 level system, closest to L* (Lightness), but not Lightness
> 
> https://en.wikipedia.org/wiki/Lightness
> 
> <https://en.wikipedia.org/wiki/Lightness>
> 
> see gamma ...,
> 
> https://en.wikipedia.org/wiki/Gamma_correction
> 
> <https://en.wikipedia.org/wiki/Gamma_correction>
> 
> Kinda depends on what you are working with ... calibration or 
> characterization? sometimes calibration is "good enough" 
> characterization ...
> 
> to answer your second question it looks like you already know the 
> exposure (pixel density discussed above) ... invert equation for density
> 
> to answer you first question ... How do I find density? ... unless it is 
> linear with exposure, or you have beforehand design knowledge of the 
> system, you will have most likely have to measure
> 
> 
> 

apologies gamma 1.8 instead of gamma 2.2 might be closer to L*  with 
white point of 5000K

-- 
dale - https://www.dalekelly.org/
Not a professional opinion unless specified.

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image density, log exposure (-target density) and pixel level imran.kanjoo@gmail.com - 2019-01-26 00:34 -0800
  Re: image density, log exposure (-target density) and pixel level dale <dale@dalekelly.org> - 2019-01-26 16:19 -0500
    Re: image density, log exposure (-target density) and pixel level dale <dale@dalekelly.org> - 2019-02-05 18:19 -0500

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