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You are here: Home / The Last Word / Sony a6300 — digital filtering at high ISOs

Sony a6300 — digital filtering at high ISOs

March 11, 2016 JimK 2 Comments

This is part of a long series of posts about the Sony a6300. The series starts here.

In the post before the last one, I showed a kink in the noise vs ISO setting curve for the a6300 that occurred at high ISO I suspected digital signal processing, specifically, low-pass filtering.

The way to detect this is to look at the frequency response of the read noise. If it’s flat (except for some thermally related stuff near dc) then the camera’s firmware has — quite properly, IMO — kept its mitts off the raw data, at least with respect to filtering.

I looked at the red raw channel for the single shot case. Here’s a baseline, at ISO 100.

100singleshot fft

Nice and flat. Now let’s look at ISO 430, right before the conversion gain switch takes place.

320singleshot fft

Still flat. Now 400:

500singleshot fft

That’s funny. There’s a very slight drop-off with frequency in the horizontal plane. I have no idea waht causes that.

ISO 500:

500singleshot fft

Still a little bit of droop.

6400singleshot fft

ISO 6400 is looking flat.

10000singleshot fft

So is ISO 10000. What about ISO 12800? That’s where we saw the suspicious drop in the noise curves.

12800singleshot fft

There it is. The smoking gun.

Does it persist that way at higher ISOs?

25600singleshot fft

Indeed it does.

The Last Word

← Sony a6300 — high ISO shadow color casts Sony a6300 — taming the EVF/LCD switching →

Comments

  1. Jack Hogan says

    March 12, 2016 at 1:01 am

    Jim, are the frequency plots off a single raw channel or some combination of all four?

    Reply
    • Jim says

      March 12, 2016 at 7:04 am

      The red channel, Jack. I’ll go back and make that clear. Thanks.

      Jim

      Reply

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