Unaltered raw VS mildly post processed raw - any real diff?

[samester]

Hey ppl,

Just wondering what the subtleties are between compensation before and after a raw pic is taken.

For example if I set my D70 to WB auto with some comp, it's generally ok on a sunny day but when using fill flash in certain modes it usually needs to be warmed up a little. I could change the WB settings to optimise the colour temp but it's much quicker to shoot with a known suite of settings that'll work 80% of the time and correct WB in nikon capture.

The crux of my question is, will a perfectly exposed RAW be appreciably different to one that has been mildly post processed (i.e. slight WB correction or exposure comp in nikon capture.

I know that in theory the perfectly exposed pic has more info etc etc but practically if I wanted to print a full page pic in a glossy colour mag for example, would there be a visible difference?

Cheers,
Sam

[Aussie Dave]

Hi Samester
I'm sure I'll be told I'm wrong, if I am, however I don't believe WB has anything to do with correct exposure. White Balance basically tells the camera how to manipulate the various tones/shades of colours, "after" the image is taken.

This is why you can manipulate the WB (and also exp. comp.) of a NEF/RAW image, on the PC afterwards....as the NEF file hasn't created the final image yet, it is only a memory of what the CCD saw (with a few mathematical algorithms thrown in for good measure)

In theory, I don't think it would make any difference.

If I am incorrect here, please enlighten me.....

[xorl]

Dave is right. White balance is done in software, either on a PC or in the camera itself. Any white balance changes you make when processing the raw file will give the same result as a raw file with the white balance correctly set at capture time. As an aside, I've seen some hints which suggest it might be slightly different on the D200, some white balance may be performed at the AD conversion stage in the camera - but I'm not sure.

However, exposure compensation during raw conversion is different. -EV compensation (making the image darker) will basically give the same result unless the image contains highlights which have blown out (making it much worse). Theoretically there is an advantage to doing this with a fully 16bit workflow, in practice people debate this. Have a look at discussion on "expose right" for more details.

+EV compensation (making the image brighter) will increase noise visible in the image. This is may be ok, but getting the exposure right in the first place is always better.

Hope this helps.

[samester]

Dave is right. White balance is done in software, either on a PC or in the camera itself. Any white balance changes you make when processing the raw file will give the same result as a raw file with the white balance correctly set at capture time. As an aside, I've seen some hints which suggest it might be slightly different on the D200, some white balance may be performed at the AD conversion stage in the camera - but I'm not sure.

However, exposure compensation during raw conversion is different. -EV compensation (making the image darker) will basically give the same result unless the image contains highlights which have blown out (making it much worse). Theoretically there is an advantage to doing this with a fully 16bit workflow, in practice people debate this. Have a look at discussion on "expose right" for more details.

+EV compensation (making the image brighter) will increase noise visible in the image. This is may be ok, but getting the exposure right in the first place is always better.

Hope this helps.

cheers guys.

i just want to filter through the theory to try and find some practical answers.

i've push processed slide film in the past without being able to tell the difference, i reckon pushing a raw image would be similar.

slight adjustments probably have negligable effect - ideally i'd rock up to a magazine printer, give them a few samples and get them to print a few pages for me then check for visible differences between an unaltered raw and one slightly altered.

converting raw to tiff for printing would be more of an issue quality wise i imagine.

sam