ISO on a digital camera

[page3]

We were chatting in the office, what does it actually do if anything when taking in RAW?

[Scott330ci]

Same as it does when shooting in JPEG

[bramley]

Eh? Increasing ISO increases the sensor's sensitivity to light, whether it's in jpeg or RAW mode, the function is the same.

Or am I missing the point of your question?

[Bee_Jay]

http://blog.dpreview.com/editorial/2009/09/sense-a... + http://blog.dpreview.com/editorial/2009/09/moving-...

[Scott330ci]

As I understand, I think he means you can take practically an underexposed photo (so much so the photo looks black) and still recover it, so why use the ISO function?

[page3]

I was under the impression that RAW takes a snapshot of what the sensor is seeing, so why would sensitivity come into it?

I understand what is does on a film camera.

Perhaps I'm just being dim.

[Bee_Jay]

ISO picks the brightness 'middle' level that the image is recorded at (i.e. the amplification level)

Since RAW files contain way more depth of detail (12-14 bits) than an 8-bit JPEG you can usually rescue 3-4 stops rather than about 1-1.5. Still better to shoot the image at 800 ISO in the first place in RAW than shoot everything at 100 ISO and rely on RAW to magic things out of the dark for you... ;-)

[page3]

Ah I see. I knew I'd get a sensible, concise answer here

[_dobbo_]

If in doubt, give it a go - pull the exposure up on an underexposed RAW file vs increasing the ISO in a camera.

There is a limited amount you can do with a RAW file, before you get ridiculous amounts of yukky noisy areas in the shadows.

[bunyarra]

The data recorded in a RAW file is dependent on the ISO setting used to capture it. It is as hard coded in RAW as your shutter speed, F stop and focal distance. RAW is just that - the dump of the sensor at that moment in time.

You indeed cannot decide you want an ISO 100, noise free image if you capture it at ISO 800 and find it is riddled with horrible coloured dots in the shadows (and the reverse obviously applies).

The variable RAW elements are primarily white balance - you can adjust this however you wish while having little or loss of data. You will also find, depending on the camera, that there is some more information stored in the RAW data at the edges of the histogram (under exposed and over exposed). Using Photoshop etc. you can "pull" or "push" this data into the image and can sometimes recover information otherwise lost if it was a JPEG capture.