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Re: Sony FX9 camera test

Re: Sony FX9 camera test


Hi again Alfonso.

Sony’s logic when designing their cameras and determining base ISO appears to be based on finding the sensors clip point and working down from there. So where you have a 460% curve such as S-Cinetone you design the curve so that 100% sensor output = a recording level of 109IRE and then go down 11 stops from there to black. This will give a good SNR while making use of the sensors full highlight range, the shadow range is limited by the gamma curve, but the shadows remain clean because you are putting a good amount of light onto the sensor.

Then for S-Log3 you put 100% sensor output at 94IRE (the clip point of the S-Log3 curve) and go down 15(ish) stops from there. This results in a reduced SNR, the impression of a greater highlight range (because you putting less light on the sensor) while the gamma curve extends deeper into the shadows and noise, so overall greater DR but at the expense of more noise than S-Cinetone.

Because S-Log3 has 6 stops from clip to middle grey and then S-Cinetone has 4.5(ish) stops from clip to middle grey, you need to expose S-Cinetone 1.5 stops darker than S-Log3 to put middle grey in the right place and achieve the full dynamic range without clipping the highlights. So S-Cinetone ends up with a base ISO rating that is almost 1.5 stops lower than S-Log3.   

The base ISO for all the STD gammas as well as HG1-4 is 320/1600. HG7 & HG8 are 500/2500ISO (they have a greater highlight range than S-Cinetone so as above they are rated higher so you expose the sensor lower to gain the extra highlight range).

Sony don’t give a middle grey value for S-Cinetone because the idea is that you adjust your exposure to make use of the roll-off that starts around 65IRE to alter the contrast in your upper mid range and brighter skin tones to provide more or less contrast depending on the look you want. There is also a very small change in the gain in the toe of S-Cinetone that has a similar effect to shadow contrast - brighter = less, darker = more. My own testing suggests that to match the 320ISO base rating that you would expose middle grey at 44IRE and a 90% reflectivity white card at 78IRE. There is a white paper on S-Cinetone: https://pro.sony/s3/2020/03/24095333/S-Cinetone-whitepaper_v2.pdf

Alister Chapman 

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On 17 Apr 2021, at 16:06, alfonso parra <info@...> wrote:

We decided to use the dual ISO base settings ​​for all the curves and thus be able to compare them to the same ISO value, in this case with the cinetone curve we use 800 as for the Slog3 curve so that we can clearly see the differences. If it is interesting to observe how you have made, the curve with different ISO values ​​and compare the results. What surprises me is that by raising the value of the S-cinetone to 800, detail is lost in the highs when normally the opposite happens, by increasing the gain, or the ISO value, the ability to collect detail in the highs increases, losing in the shadows. I don't remember now, but does Sony make any recommendation on the ISO value to use with the S-cinetone or does it indicate how much the middle gray value should be? May I ask you how did you get to 320 ISO in relation to 0db? In the theoretical sensibility test that we did, it gave us that the 800 ISO would be 0db considering the STD5 curve with gamma 2.4, which is actually quite similar to S-cinetone, actually the most similar is the STD3 only that S-Cinetone compresses something else in the highlights. 

Alfonso Parra ADFC
Tel Colombia 57 311 5798776
Tel Spain 34 639109309
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