RAW Histogram "calibration"

Hi there,
 
I am a new user of FRV.
I am trying to get along with the RAW histogram and get it properly calibrated for my camera SONY ALPHA A7III
from the manual I read:
the underexposure indication limit (meaning the dynamic range of the camera) can be set even more flexibly, depending on the ISO settings. For this, one needs to turn on the Preferences – Image Display - Exposure - ISO-based underexposure limit setting and set three parameters for the camera: underexposure level (dynamic range) for ISO 200, ISO 1600, and “for high ISO.”
Calculating the Underexposure Limit (dynamic range) will happen in the following manner

  • For ISO values of 1600 and lower, down to ISO 6, the linear change is such that the line passes through the value for ISO 200. In other words, the line passes through two user-defined points: ISO 1600 and ISO 200.
  • For ISO settings 1601 and above, the dynamic range decreases by one stop for each stop of ISO setting increase, but the limit is always greater or equal to the value that is entered for high ISO.

A7III is ISO-invariant and DR can be seen here
So basically ISO invariant from 100 to 500 and from 640 onward.
How can I properly calibrate RAW histogram in FRV?
Right now, all default settings I have a scale from -10/UE-4.6/+3. Does it already take into account the camera properties?
Thanks

Dear Sir:

Lower (shadow) end of usable dynamic range is matter of

 - personal taste (noise tolerance)

 - typical image editing/retouching patterns (do you usually 'open shadows' /made it brighter/?)

 - output media size (the larger the print, the less acceptable noise)

 - output media type (e.g. matte paper will hide some shadow color noise due to ink spread)

So, it is very hard to suggest some specific numbers for specific camera. Default values (9/7/3) are conservative enough for today full-frame cameras, and rather optimistic for micro-4/3 and large sensor compacts.

Please note:

  1. FRV defines dynamic range from 'overexposure limit', so it is full DR, +3EV (from midtone to saturation) is already included in calculation. So, 4.6stops @ISO1600 looks too conservative to me. I have not used A7III, but for A7RIII I prefer something about 6-7EV@ISO1600, depending on print size.
  2. Published DR values may be normalized for some standard output size (e.g. 8Mpix in DXOMark default plot). This allows inter-camera comparison 'in same conditions', but overestimates DR range for the case when full resolution is used (due to large pring and/or cropping)

Many thanks for your quick reply.
 
According to A7III ISO/DR chart I set the values as follows:
10.5EV @ISO200, 8.5EV @ISO1600, 3.5EV @high ISO
is it too agrressive?

Dear Sir:

as mentioned in my initial reply, useable DR depends on may aspects, both personal (noise tolerance) and output type/size (larger prints are less tolerant to noise because on small prints values are averaged, so noise is less).

So, any specific value suggestion are incorrect because specific subjective (personal) and objective restrictions are not taken into account.

Meanwhile, 10.5EV @ISO200 looks ok (for me!) for A7III (assuming it is more or less the same as my A7R-III). I mostly do not use high ISO values on any camera, so could not suggest anything for higher ISOs (I use 6-7EV for ISO 1600 point, but this value is rarely used in my real culling, because used ISO range is mostly limited to 100,200, 640).

 

thank you
If I understand correctly, the UE value is the exposure below which shadow recovery does not "look good" anymore, right?
 

Generally - yes. Devil is in details as usual: if you decrease print size (to, for example, 4x6 in, or for web-sized FullHD (2Mpix) or even less), then several pixels will be averaged to make single output pixel, so noise will decrease due to pixel averaging.

That's why it is impossible to select single 'UE level' suitable for all cases.

in an ISO-invariant regime, should the UE value be constant?

In ISO-invariant mode  DR drops by 1 stop on 1-stop ISO change

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