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Custom White Balance (Canon 20D - notes)
Old 11-11-2004, 04:52 PM   #1 (permalink)
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Based on the thread titled "Camera Calibration?", I thought the following might be interesting to some. While I was using the 20D, the same information applies in general to all of the digital SLR cameras.

When you are shooting under more or less fixed lighting situations, then it is often wise to use a custom white balance rather than just AWB. For the 20D, you take a photo of a white or gray card and then make that the reference photo for the 20D Custom White Balance setting.

Contrary to what many will say, it makes no real difference whether you use a white card or a gray card for the reference image. Here are two photos which illustrate this point:





Both of theses shots were made in identical CFL light. These are the actual images, cropped and resized, but otherwise as is. I changed the custom white balance in the 20D between each shot.

Just for reference, here is the same shot with the same CFL lights shot with AWB:



If you shoot RAW only, then you don't need to worry about White Balance. But if you shoot combined, then it is wise to get the white balance right. That being said, I use Custom White Balance whether I shoot RAW or not.

Another note: Place a white coffee filter over the lens and shoot the scene in the light you're balancing for. Use that image as the CWB reference image. Gives the same results as above.

Also note, that it can be very helpful to calibrate the meter on the camera. I use a Black/White/Gray target for this and the camera's histogram. I find the 20D much closer to the proper exposure than the 10D was. But my flash meter is generally up to 1 to 1 1/2 stop different, so I adjust the camera appropriately.

Cheers,
rfs
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Re: Custom White Balance (Canon 20D - notes)
Old 11-11-2004, 05:13 PM   #2 (permalink)
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Terrific info! Thanks!

Dave
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Re: Custom White Balance (Canon 20D - notes)
Old 11-11-2004, 07:31 PM   #3 (permalink)
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QUOTE: "If you shoot RAW only, then you don't need to worry about White Balance."

I seem to recall just reading how that statement is completely wrong, I will try to find out where I read that...


anyone else?
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Possible reason?
Old 11-11-2004, 08:36 PM   #4 (permalink)
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Many of the SLRs that let you shoot in RAW, also imbed a JPEG in the file or store it as a seperate image. The Canon 10D is an example of one that imbeds the JPEG, whereas, if you choose the 20D gives you a RAW image and a JPEG file. If one has a JPEG file being written along with the RAW file, then one would want to have proper white balance otherwise the JPEG will be of diminished value. But if you shoot only RAW (and there is no JPEG), then you have the same data that the camera actually saw (the data that hit the sensor). Then at RAW conversion time, you can choose "as shot" or any of the other white balance settings, or you can customize the conversion for any setting you want. As a result, in this case, the white balance you shot the photo with is of low significance. However, if you were going to auto convert a large number of photos, it would allow you to convert them all "as shot". But with something like Photoshop CS and its built in ACR (Raw converter), you can just convert one photo and customize the RAW conversion settings and then automatically convert all the rest using that custom setting.

By the way, here is what Adobe says about this topic:

Adobe article on subject



Cheers,
rfs
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Re: Sounds reasonable, but
Old 11-12-2004, 12:56 PM   #5 (permalink)
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I did find the article, it is on the very last page of the current (Nov/Dec) issue of Digital Pro Photo, I reread it this morning and would have to agree that the writer also makes sence.

I would love to hear your take on that article...

thanks...
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Re: Sounds reasonable, but
Old 11-12-2004, 02:19 PM   #6 (permalink)
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Steven,

I too read that article and found a few flaws in it. To illustrate this best, let me break down my workflow.

I capture in RAW only. I don't really care about the embedded jpg. I do try to get the color temp right in camera. I find it's way easier to get the exposure correct than the color temperature. For some reason, I really like a warmer image than what I set up my camera for. Sometimes, when I am at the back of a church and shotoing the first kiss all the way up at the front, I am forced to underexpose or choose to because I don't want to use ISO 800.

Next, I go to my machine and get into post processing. My post processing machine is an Athlon AMD 64 w/1 gig of RAM, a 256MB GeForce graphics card, one 200 gig (partioned into 2 100 gig) hard drive and a 40 gig (for OS and software), and a 19" LCD. My Dell (backup machine) is a 2.4 P4 w/512 MB of RAM.

So now, I have all of my images loaded to my machine. I keep them in the default folders that the camera creates for me. If you have 300 images in one folder, each time that PS CS browser goes to load the folder, it has to load the previews. Even if the browser was open in the background while you worked on an image. I group the images together in groupings that have similar color temps and exposures (ie under or over). Then, I open one image and make adjustments to the RAW data. Here's the fun part. See RAW is a format that saves an uncompressed collection of alogorithms proprietary to that brand camera. You change color temperature across the whole range with no quality loss. Adobe claims that you can change exposure by 2 stops with no loss in quality. I don't see that, so I am comfortable with about 1 stop. These changes are made before it becomes a jpg. After I make those changes, it opens as a jpg and I close it without saving. Then, I go back to the browser, select all of the images in that group, and right click on one of them. I then select to apply RAW conversion using the 'first selecting image'. PS makes all of the conversions I just did. Tweaking 10 or 15 images may take 5 minutes.

That article did make some pretty good points. It is always better to get it right in camera. I will agree with that. I think what they were leaning towards was seeing RAW as a 'fix all', which it clearly isn't. If your exposure is off by more than 2 stops, RAW conversion definately won't help you. However, if your color temperature is off by 5600K, then a quick RAW conversion in PS can fix it with no image quality loss and very little time.

Now, if you use AWB, your post processing time can increase because you have more variables each time the camera gets to choose. But, if you select the most appropriate WB and stick with it, then you have fewer groupings to fix and it takes you less time.

Mike
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I don\'t have the article ..
Old 11-12-2004, 05:59 PM   #7 (permalink)
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I don't have that magazine available currently so I can't read the article. What was his major point or argument?
Keep in mind that the RAW data will be the same no matter what color balance you set at the time you take the photo. The white balance choice will be written only to the **** data.
I still like to get the white balance right in any event. Why get sloppy?
Cheers,
rfs
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