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How to read SONY A7SII's histogram correctly?


coco

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Hi I'v been using SONY A7SII for over a month. it is a great camera in many ways. except the  8-bits 4:2:0 internal recording. But I think it is the necessary tradeoff. because if you sonsider the marketing role and the consumer affordable post editing for 4K .
back to my question. I found the histogram of SONY a7SII acts differently in different picture profile. I mean, If you apply PP7/PP8 or PP9 (in other words, you shoot in S-Log2 or S-Log3). The Histogram it can show is constrained, I mean even it you over expose, the range of histogram is limited,. (please check this https://www.dropbox.com/s/50gn80oadrl73z5/oveExporsureOfPP8.jpg?dl=0 way over exposed in PP8) even you crank up ISO up to the maximum, the spike of histogram won't go to the right.
 on the other hand, if you apply other picture profiles or even no picture profile. the histogram will act normally( please check this https://www.dropbox.com/s/1beq7m99jeqbvne/OverExposureOfpp6.jpg?dl=0 over exposure shot in PP6).
 
Can any one explain this to me?

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Guest Ebrahim Saadawi

Why is S-LOG (PP7/8) invented and available on the camera vs other modes? 

It's because, an LOG mode captures a higher dynamic range from the brightest to darkest point in the image. Meaning on the histogram, it pushes the white point to the left (in order for it not to clip) and pushes the black point to the right (in order not to clip). So, when you switch from a normal picture profiles that has crushed blacks and bright highlights (high contrast) that is more spread over the histogram and close to clipping at both ends to a LOG picture profile with higher dynamic, the histogram will be squeezed. 

This is a good thing don't be so afraid of not filling up your histogram, my testing with A7s S-LOG2 (pp7 not pp8), you can stretch the histogram and get a contrasty image without falling apart that easily, and I've found the the secret to SLOG on the A7s is to keep the histogram more shifted to the right, i.e., image a bit over exposed and bring it back down in post. 

I hope it's clear how the histogram responds to your setting changes.

 

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It is apparently because, slog has a 16-235 (or something like that) range, whereas other picture styles have 0-255 range. The histogram shows range from 0 to 255 brightness values, but slog's highest value is just 235 - not perfectly white. Same with blacks.

That doesn't mean though, that your image is not overexposed. It actually is, but it is overexposed at 235 brightness value, not 255.

When first time shooting with a picture profile, that has a max value of 235, you have to be careful not to blow out highligts. Because if you don't know, that 235 is the max, you're looking at histogram and thinking - nice, the exposure is ok - but actually your highights are blown out at 235 and there's nothing you can do about it in post.

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