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White Balance Rendering

wingman
Apprentice

Hi,

 

I have the Rebel T5i and 6D and have a technical question about how a camera evaluates the white balance and color. 

 

When is the white balance or color cast determined by the camera? Is it when light hits the image sensor or when the camera saves the data and renders it in JPEG format?

 

I'm pretty much trying to determine what part or process of the camera sets the white balance. I hope I asked this question correctly. 

8 REPLIES 8


@wingman wrote:

Hi,

 

I have the Rebel T5i and 6D and have a technical question about how a camera evaluates the white balance and color. 

 

When is the white balance or color cast determined by the camera? Is it when light hits the image sensor or when the camera saves the data and renders it in JPEG format? ...

 


Not the latter, apparently, because WB correction is applied to RAW files as well as to JPEGs. Of course in a RAW file the WB correction is more in the nature of a suggestion, because you can change it at will without penalty.

 

As for how the camera evaluates WB, the overall answer is "unevenly". My 5D Mark III does it surprisingly well, my previous DSLRs (even the 7D!) not so much.

Bob
Philadelphia, Pennsylvania USA

ebiggs1
Legend
Legend

Bob from Boston is pretty correct and on the right track.  But further, the RAW file is not altered in any way.  There is a small data file created that tags along with the RAW file.  It tells the camera and your computer how to display the RAW file.  You can not view a RAW file as it is.  It must be converted.  Even when you make post edits you do not alter the RAW file.

 

So this is why RAW is best because you apply WB after you take the shot.  With jpg or tiff, it is applied when you take the shot.

It is a guess at that point and why people alter it later in a post editor.  Your eye is pretty well adapted to fooling your brain to see what you want to see.  The camera sees what is there!  Your camera has several settings to help in this guessing process.

EB
EOS 1DX and 1D Mk IV and less lenses then before!

TCampbell
Elite
Elite

I'm not sure if it matters.  

 

But more to the point... I would avoid ever using "auto" white balance and for two reasons.  (1) It's generally the least accurate way to set white balance, and (2) it may even vary from frame to frame depending on background.   If you know what sort of lighting you have (e.g. full sun, cloudy, tungsten, etc.) then you can pick the mode and at least if you do that you have a "fixed" white balance that will be consistent (even if it's wrong... at least every frame is uniformly wrong and that makes it easier to fix the entire shoot so that they're all synchronzied to the correct white balance.)

 

But the better way to set white balance is using a white balance tool for it.  I use a "gray card".  The card (my "card" is actually a commercial fabric on a folding spring form called a Lastolite EzyBalance) is formulated to be color neutral (the gray is a true gray and doesn't tend toward red, or blue, etc.)    There are also white balance caps, such as the Expodisc.  

 

To use the tool in JPEG mode, you take a photo of the gray card (the card should be centered in the frame... it doesn't need to fill the frame, but it does need to be in the center and not off to one side) or take a photo with a white balance cap on the camera.  Also, the card doesn't even need to be focused.  With a long lens, you may be so close that you're inside the minimum focus distance and some photographers feel it's better to be deliberately out of focus when you shoot the card.  The card MUST be in the identical lighting that you intend to use for your subject (usually you just put the card in front of your subject for a moment, take the image, and then remove the card and put it away.)

 

 

You navigate to the white balance menu and pick "Custom" white balance.  The camera will prompt you to select a reference image and by default, most Canon cameras will display the last image you shot (which probably is the image of the gray card.)  But if not, you can select any image on the card to find the one with the gray card.  This set that image as the Custom white balance image... but... YOU STILL NEED to set the white balance mode to "Custom" (don't forget to do both if you shoot JPEG.)

 

Now, every shot you take (as long as it's in that same lighting) will have perfect white balance.  Just remember that if you change lighting, you need to repeat this, but every shot you take will have that white balance applied until you change white balance mode.

 

If you shoot RAW instead of JPEG, just take a photo with the gray card anywhere in the image (but in the same lighting you plan to shoot your subject).  White balance for RAW is applied on the computer during post processing... not in-camera.  You just need to have captured one image that has the white balance aid.  On the computer you'll set white balance and typically there's an eyedropper tool.... and you'll go pick a pixel on the gray card from your reference photo -- white balance is now set.  You can then copy/sync that white balance adjustment to all of your other images (e.g. Lightroom supports this, as does Photoshop, I previously used Aperture and it also supports it.)

 

 

Tim Campbell
5D III, 5D IV, 60Da


@TCampbell wrote:

I'm not sure if it matters.  

 

But more to the point... I would avoid ever using "auto" white balance and for two reasons.  (1) It's generally the least accurate way to set white balance, and (2) it may even vary from frame to frame depending on background.   If you know what sort of lighting you have (e.g. full sun, cloudy, tungsten, etc.) then you can pick the mode and at least if you do that you have a "fixed" white balance that will be consistent (even if it's wrong... at least every frame is uniformly wrong and that makes it easier to fix the entire shoot so that they're all synchronzied to the correct white balance.) ...

 


I usually agree with Tim, but not this time. At most of the shoots I do, consistent light is a rarity, so I'd have no idea how to sensibly override auto WB. Yesterday I was editing some pictures I had taken on a trek through a wooded park in the Philadelphia suburbs. The sun shone through from various directions at various strengths; clouds came and went; and the light got dimmer and redder as time wore on. And on about half the shots I was using fill flash. My 5D3, set to auto WB, did a much better job of keeping up than I would have done manually and without the hassle of continually checking a gray card. I ended up correcting some of the shots, but a correction of around 200 degrees K was usually enough to get it right.

 

I also worked on some pictures I took at a 4th of July parade the next day. The day was overcast, and the light was very consistent, and I probably could have used a manual setting. But that also made it easy for the camera, again set to auto WB, to get it right. While I made some brightness and contrast adjustments, I don't believe I changed the WB on any of the shots.

 

There may well be situations when I'd override auto WB. But my experience is that those are few and far between.

Bob
Philadelphia, Pennsylvania USA

ebiggs1
Legend
Legend

Bob from Boston, I mostly agree with Tim's dialog. Except, who carries a 18% gray card?
I still maintain post is where it is at. Shoot RAW and don't fret it. Of course you know I am high on post editing.

EB
EOS 1DX and 1D Mk IV and less lenses then before!

ScottyP
Authority
Although on a different note, the "Auto" WB setting in Lightroom is a surprisingly good place to start fiddling if you get an image with poor WB out of camera. Sometimes it is so good that is the end of the story and you don't need to get into the eye dropper or the sliders. It is pretty rare that I stop to place a white/grey card in the scene, though I frequently wish I had.

Other times not.
Scott

Canon 5d mk 4, Canon 6D, EF 70-200mm L f/2.8 IS mk2; EF 16-35 f/2.8 L mk. III; Sigma 35mm f/1.4 "Art" EF 100mm f/2.8L Macro; EF 85mm f/1.8; EF 1.4x extender mk. 3; EF 24-105 f/4 L; EF-S 17-55mm f/2.8 IS; 3x Phottix Mitros+ speedlites

Why do so many people say "FER-tographer"? Do they take "fertographs"?

Thanks for the replies. My understanding now is the white balance correction is made after the RAW file is created. No change is actually made to the RAW file. WB correction is applied when the camera shows a JPEG file on the LCD, or when editing in post. 

I have a 1D Mark IV. I generally shoot AWB and camera gives good results. When the shot WB looks off on LCD I try selecting specific settings. I have never found a specific setting that improved on what AWB did. As Ernie says, post will resolve the issue.
John Hoffman
Conway, NH

1D X Mark III, Many lenses, Pixma PRO-100, Pixma TR8620a, LR Classic
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