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Groups > sci.image.processing > #4419 > unrolled thread
| Started by | imran.kanjoo@gmail.com |
|---|---|
| First post | 2019-01-26 00:34 -0800 |
| Last post | 2019-02-05 18:19 -0500 |
| Articles | 3 — 2 participants |
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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
| From | imran.kanjoo@gmail.com |
|---|---|
| Date | 2019-01-26 00:34 -0800 |
| Subject | image density, log exposure (-target density) and pixel level |
| Message-ID | <51c0a60e-9498-4d22-9f3d-3a63b85c12b0@googlegroups.com> |
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.
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| From | dale <dale@dalekelly.org> |
|---|---|
| Date | 2019-01-26 16:19 -0500 |
| Message-ID | <buf8ef.irj.19.1@news.alt.net> |
| In reply to | #4419 |
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 -- dale - https://www.dalekelly.org/ Not a professional opinion unless specified.
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| From | dale <dale@dalekelly.org> |
|---|---|
| Date | 2019-02-05 18:19 -0500 |
| Message-ID | <bv9r72.1sr.19.1@news.alt.net> |
| In reply to | #4420 |
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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