# How much resolution decrease as we raise the ISO ?

Started May 18, 2012 | Discussions thread
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 Let's make the conditions clearer - In reply to Silverback1988, May 19, 2012

1 - How does DR change w.r.t. ISO?

For example, with Canon cameras, the change in DR at the lower end is not linear: ISO 100 is only marginally better than 400. With the latest Sony sensors, it seems more or less linear, though.

2 - What kind of resolution are we talking about?

In other words, what is the native contrast of the target, assuming we are using some kind of line pattern similar to the ISO 12233 test chart?

3 - What is the noise reduction technology used?

Linear space-invariant filtering is perhaps one of the most naive way and impact resolution the most. This, however, could serve as a lower bound - meaning, ISO 6400 perhaps offers AT LEAST half the linear resolution of ISO 1600.

With high-contrast, well-structured targets, sophisticated image noise reduction algorithms are able to differentiate signal and noise clearly, and process accordingly. After processing, say, an ISO 1600 image of the 12233 target may well have the same measured resolution as the ISO 100 image. However, this does not mean all natural images will look the same - we have a lot of seemingly random and subtle details submerged by noise and they are difficult to recover with any noise reduction method. The perception here is not a loss of resolution but a somewhat unnatural imbalance in different frequency and contrast components - sometimes as watercolor effect or being plastic/wax-like.

Silverback1988 wrote:

Hi,
I curious if someone of you has been calculate this.

As we know, if we keep the noise constant by applying NR, then there would be a decrease in resolution as we raise the ISO.
But by how much from the native resolution ?

For example we had 20 MP camera.
Say we are able to get the full resolution of 20 MP is on ISO 100.

As we raise the ISO, say ISO 1600, then we keep the noise similar to the ISO 100 by applying NR. How much resolution is left ? Surely is not 20 MP anymore.
Would be it 5 MP only ?

I think we could compare it with a 5 MP camera and then shot with ISO 100.
If the picture is identical then the resolution is the same.

And I think the decrease is not linear between ISO 100 and ISO 400.

Opinions are welcome.

Sorry, English is my third language
I hope I state my question clearly.