Atherton & District Amateur Photographic Society

Please note that I do not care whether you are shooting JPEG or RAW. Its a free world so get on with it.

What has been really troubling me is the issue of correcting the white balance of an image taken in mixed lighting. And whether correcting a JPEG is the same as correcting a RAW file.
This was highlighted in the Rylands library post.
So I have done some testing.

I set up a black piece of board with an 18% greycard in the middle and some strong colours around the edge.
The only light source was a table lamp. The camera was set to daylight white balance, spot measuring but no other changes were made to the standard settings of my Canon 40D.
I took a JPEG and a RAW image.
Next both images were pulled through Camera RAW and Phase One where the only adjustment made was to correct the white balance by using the eyedropper on the grey card. All other corrections were switched off when converting the RAW to JPEG. The results were surprisingly different.
From the pictures below you can see that the best results were obtained using a RAW file in Camera RAW. It is clear that you should not use Phase One to correct JPEGs as it gives a strong green cast (which was also seen in the Rylands one)
I was able to correct the "corrected JPEG" from Camera RAW to be very nearly the same as the RAW by using channel mixer. I did not manage to correct the original JPEG in Photoshop.
I learned something and hope some of you will find this of interest.

Theo

If the only light source was a table lamp, the appropriate JPEG white balance setting would be Tungsten (Incandescent in some menus). What you have here isn't mixed lighting, but an alternative light source.

Mixed lighting would be say daylight through windows combined with tungsten bulbs or fluorescent. That is a problem whatever you do with it. In that case I'd see what AWB did and use Daylight if that seemed better.

Theo Dibbits wrote: What has been really troubling me is the issue of correcting the white balance of an image taken in mixed lighting....
The only light source was a table lamp. The camera was set to daylight white balance....

Hi Theo

Perhaps the best course of action is to be prepared in advance if you know that the lighting is going to be uncertain.

I shoot in mixed lighting on location almost all the time and I get around it by carrying a Digital Grey Kard in my camera bag and taking a test shot at the start of the shoot which is then used in the RAW conversion. Such a device would have been handy in the John Rylands shoot.



Link to Digital Grey Kard on Amazon:
http://www.amazon.co.uk/Digital-Grey-Wh ... 789&sr=8-1


Having said that, I quite often deliberately use the 'wrong' white balance setting when processing an image for effect.

Hi,

Put this on one of my websites, a few years old now, but some may find it interesting, not only about different light sources, but the colours emitted by lights and how shutter speed can also affect the resulting image.

http://www.oakeycoke.co.uk/portraits.html

You may need to turn your speakers up or down depending on whether you like the background music, something i was experimenting with at the time. (must do some updating sometime)

Phil.

PS. You Canon users should be using DPP, its free and its the only program that knows Canon algorithms, compression, lens distortion etc.