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Question about Log and Lin encoding of raw

log lin encoding raw

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#1 Julien Ramirez

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Posted 26 May 2015 - 01:24 PM

Hello Everyone!

 

Sorry my English is bad, I’m Belgian. I have to say I’m new to all this , log etc. I’m in a Film school in Belgium.

 

Often on forums and informations about Log encoding I see that it allows to allocate more code value in the range of shadows by giving the equal number of values in each stop of dynamic range. I think I understand the principles of Log Vs Lin. The fact is linear encoding gives too much code values to the highlight where the eye is not able to see the tiny changes in brightness in the higher stops.

 

But I’m not sure, I understand everything. If the ADC in most of the sensor is working in 16bit linear, so the 10 th stop under full well capcity has just 64 code value. I could do 12 bit log and have about 300 values per stop (I know, It’s not exactly equal but it’s to make the point) but I’m wasting many values since the 64 values I got is all I can get, right?

 

Is that possible to have an ADC that quantizes the analog signal directly in log, would it be better?

 

I red a lot on this forum and on websites but I’m not sure I’m understanding it all. I am not an engineer or anything, I am just curious of understanding the process, If someone could enlighten me?


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#2 David Mullen ASC

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Posted 27 May 2015 - 12:09 AM

ArriRaw is 12-bit Log...


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#3 Julien Ramirez

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Posted 27 May 2015 - 12:33 AM

Indeed, i understood That it has a dual gain amplifyer and two 14bit adc and so arri combines the two in one 16bit linear signal. So arri is doing 12bit raw log from 16bit linear, correct me if i am wrong?

I am not trying to say That it is bad or something but Just understand the principles.
In fact, my first question is, is it right That if i have a 16 bit linear file from which i did a 12bit log i am Just getting rid of some values in highlight but not gain any precision in shadows and midtones. So if they were 64 values in one stop in the 16bit linear i Will not gain more 'shades of gray' by encoding this stop with 300 values in log?

Thank you David for your answers, i read you on this forum for a long time and it has helped me à lot. These questions must seem stupid to you.
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#4 Julien Ramirez

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Posted 27 May 2015 - 12:35 AM

Indeed, i understood That it has a dual gain amplifyer and two 14bit adc and so arri combines the two in one 16bit linear signal. So arri is doing 12bit raw log from 16bit linear, correct me if i am wrong?


I am not trying to say That it is bad or something but Just understand the principles.
In fact, my first question is, is it right That if i have a 16 bit linear file from which i did a 12bit log i am Just getting rid of some values in highlight but not gain any precision in shadows and midtones. So if they were 64 values in one stop in the 16bit linear i Will not gain more 'shades of gray' by encoding this stop with 300 values in log?

Thank you David for your answers, i read you on this forum for a long time and it has helped me à lot. These questions must seem stupid to you.
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