RAW vs JPG shutter speed/ISO

[aboulfad]

I’ve been learning and experimenting to understand better how to use my iPhone in low light scenarios, and something recently surprised me.

I took identical shots in auto mode in both JPG and RAW with identical lighting conditions and noticed that the ISO is much lower in JPG vs RAW. Granted that the camera processes the captured sensor data in many steps to finally come up with the JPG, including noise reduction. Is that NR post processing somewhat reflected in the ISO field in the EXIF data?

If yes, then the software somewhat must derive that ISO number from some parameters?

or is the ISO influenced by the shutter speed that seems to be slower for JPG shots?

PS: not directly related to retouching but some folks here are quite techie!




Jpg (lower ISO) and RAW (higher ISO)

 

[981S]

To get the same exposure with a faster shutter speed, at the same aperture, the camera needs to crank up the ISO.

I don't know what app you are using to take the pictures, but it looks like the choice of shooting jpg or RAW has an impact on the combination of aperture/shutter speed/ISO that the camera chooses.

Anyway, the lower ISO that it is showing in the jpg is not from any post processing, it is just that because it was shot at a lower shutter speed, more light hit the sensor and therefore the signal required less amplification to reach the same exposure, i.e. a lower ISO.

 

[aboulfad]

Interesting... the attached screenshot was from LR mobile camera app. But even other RAW capable apps behaved similarly. (Camera-M, Halide,...)

 

[Doug Haag]

To get the same exposure with a faster shutter speed, at the same aperture, the camera needs to crank up the ISO.

I don't know what app you are using to take the pictures, but it looks like the choice of shooting jpg or RAW has an impact on the combination of aperture/shutter speed/ISO that the camera chooses.

Anyway, the lower ISO that it is showing in the jpg is not from any post processing, it is just that because it was shot at a lower shutter speed, more light hit the sensor and therefore the signal required less amplification to reach the same exposure, i.e. a lower ISO.

To me, a key question is which came first, the chicken or the egg?

Oops, I meant to say did the iso change come first which demanded an offsetting change in shutter speed? Or did the shutter speed change first and demand a change in iso? Apparently these mysterious setting adjustments are not being controlled by the photographer (er, telephone operator).

 

[aboulfad]

For this experiment, I used auto mode but most other cases I manually set ISO and or shutter speed.

Though the key observation is the difference between RAW and JPG choice of shutter speed/ISO. Maybe we won’t know as this is internal workings of iOS.

 

[SoCalWill]

My guess is that the camera is giving you a sane shutter speed/high ISO with the JPG because it's using noise reduction, whereas the RAW has no processing to remove noise so it's giving you a dangerously slow SS so the ISO will be low as well.

 

[981S]

Interesting... the attached screenshot was from LR mobile camera app. But even other RAW capable apps behaved similarly. (Camera-M, Halide,...)

Just installed Lightroom CC on the iPhone. Here I don't see this happening. Both jpg and RAW formats, shot in auto mode give the same ISO/shutter/aperture.

 

[aboulfad]

In dark conditions? iPhone X or Xs? After you confirm, maybe I’ll erase LR and reinstall. Thanks for trying.

 

[981S]

It's on a iPhone SE, in a dimly rit room both shots were 1/17s, f/2.2 and ISO 500.

 

[aboulfad]

It's on a iPhone SE, in a dimly rit room both shots were 1/17s, f/2.2 and ISO 500.

That made me think a bit, I dug up my iPhone 6s and did the same, the shutter speed is the same and the ISO is closer than on iPhoneX. So there must be some different processing being done on iPhoneX...