Misconceptions about ISO speed and how it really works

Things I’ve heard and read about ISO film speed in digital cameras that are wrong:

“Raising ISO…

  • makes the sensor more sensitive to light.
  • makes the sensor collect more light.
  • groups pixels together and adds them up.

In reality, ISO film speed in a digital camera is nothing more than signal amplification, like turning up the volume on a HiFi sound system: Analog signal gain inside the sensor up to some level and digital multiplication after analog-to-digital conversion (ADC) beyond that.

For example: A camera’s sensor can apply 10X signal gain to its output, i.e. ISO 1000. Setting it to ISO 1600 will perform an additional 1.6X digital multiplication on top.

This also makes it clear why raising ISO lowers dynamic range: The ADC maps certain voltages coming out of the sensor to floating point numbers between 0 and 1. Amplification on voltages that were in the high regions to begin with will end up beyond the conversible range, thus the captureable dynamic range shrinks at the same rate as ISO speeds up the film.

Digital multiplication beyond what can be amplified is less affected by this problem, as it’s obviously possible to handle and save floating point numbers greater than 1, but any such number might still appear white when viewed with a program that expects 1 to be the brightest possible value.

Digital multiplication, however, will blindly amplify anything that’s there, including noise, while there is some room for optimization with analog amplification done in the sensor. This interaction between analog and digital amplification and where the cutoff between the two lies in a particular camera explains why some cameras are more or less ISO (in)variant than others.

Cannot mount drive after unlocking with sedutil-cli

So I just did sedutil-cli --setLockingRange 0 rw "..." /dev/nvme0n1 and was still greeted with a locked drive. As evidenced by:

mount: /mnt/nvme0: wrong fs type, bad option, bad superblock on /dev/nvme0n1, missing codepage or helper program, or other error.

The solution was found in a shell script within rear, the “Linux bare metal disaster recovery and system migration solution”.

The following commands then did the trick and the drive was mountable again:

sedutil-cli --setMBRDone on "..." /dev/nvme0n1
sedutil-cli --setMBREnable off "..." /dev/nvme0n1

Looks like the drive was still expecting some pre-boot stuff to happen. The latter command disables this.

Hardware, Software, Firmware, Malware… All the different kinds of computer -wares.

Hardware

Everything on a computer you can touch. You keyboard, mouse, and monitor, but also your hard drive, CPU and power cord.

See https://en.wikipedia.org/wiki/Hardware

Software

Everything on a computer you cannot touch. Programs running on the computer, including your operating system.

See https://en.wikipedia.org/wiki/Software

Continue reading “Hardware, Software, Firmware, Malware… All the different kinds of computer -wares.”

How to completely disable Windows Update (Windows 10 Fall Creators Update 1709)

Microsoft is making it harder and harder for users to decide if and when they want to search for and install Windows Updates, assuming the average user is not intelligent enough to make such a decision for themselves.

To disable Windows Update completely execute the following commands in an Administrator Command Prompt.

Continue reading “How to completely disable Windows Update (Windows 10 Fall Creators Update 1709)”

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GiottoPress by Enrique Chavez