im not to sure if this is automatic white correction either. i tested this on a few of my photos and depending on where i click on the image iphoto would apply different tints. in all honesty it basically messed up the images. maybe im doing something wrong?

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here's how it works:
when doing a white point correction, iPhoto (in this case) takes the color value of selected point to be absolut white (and makes it absolut white, which means all color channels go to 100%).

all other colors are changed accordingly - if the red channel needs to go up 10% in order to get the "white point" white, all other colors get 10% more red too.

the black/white values (luminance, contrast) *should* not get changed (if i recall correctly).

why is this useful? well, our eyes are funny - when looking around, our eye automatically makes its own white color correction - but if we take pictures, the camera (or photo editing app) has to do that for us. good cameras actually have that feature.

example: take pictures of a snowy landscape. to your eye (without the camera) it looks white, but the picture will show the snow blueish. use white point correction, and everything looks like it should.

i wish i could explain this better, but maybe you get what i am talkign about :)

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May just be that it's a little overzealous with the other colors or just oversimplified white point correction. To try and ignore those effects, I zoomed in on several different wedding photos (yes, the dress was white... :-p ) so all I could see was white. Seems to definitely alter temp and tint to make the whites whiter. Also, the closer to absolute white the spot you click, the less effect it seems to have on the photo overall.

I'm not a digital image expert, though.

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I think iPhoto is actually adjusting the color cast of the image. Where you command-click it samples the underlying color and adjusts both the tempeture and tint to neutralize the image based on the sample point. For example, if you click on a yellow area, it will adjust the image to make that the 'neutral' point, causing a blue shift in the image (cooler). You can predict what will happen like this:
Yellow -> Blue
Red -> Cyan
Magenta -> Green

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Has any one tried this hint by clicking on something that they know should be gray, such as a gray card, or the grayish asphalt of a road? I don't have a copy of iPhoto 5, so I can't test this out myself.

However, I do have experience with Adobe's Camera Raw converter plug-in for Photoshop, as well as Nikon and Canon's RAW file conversion tools. A tool like this is generally called a white balance picker, but it's really geared towards mid-tones. When you use it to click on an pixel, it should adjust the color temperature and tint to make the red, green and blue values of that pixel equal.

There are a couple problems with clicking on something that is supposed to be white (instead of gray), such as:
• if all three color channels are already at 255 (i.e. blown out highlights), no change will happen
• if any one channel is is at 255, drastic color shifts in the other two channels may be required to bring them up to 255, which will make your image look really screwy

I'd like to hear the results if anyone can try this out.

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iPhoto is not setting the white point, it is balancing the point you click on to be colour-neutral, and adjusting the other colours in the image in relation to it. This has nothing to do with brightness. So if you command-click on something that should be neutral black or grey or white, it will make adjustments.

Photoshop lets you set independent white point, mid-grey and black points and takes luminance into account. If you have all three of those in a photo, you can correct both colour and density perfectly.

iPhoto is adjusting the tint and temperature only. Quite useful, but it may take a few tries. The thing to keep in mind is that the point you command-click on does not need to be white, it can be grey or black as well.

If your photo has more than one type of light source (sunlight, flourescent, incandescent), this will not work perfectly because the different colour "temperature" of light sources is what causes photos to be off in the first place. If you don't have a uniform colour temperature from the light sources in your photo, some things that should be white will have a blue, yellow or green cast.

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Yup, this is definitely a gray balance.

I've used it to rebalance a number of outdoor photos I took in the summer, with the white balance accidentally set to fluorescent.

It works really well, but you have to be careful what you pick because it's really easy to introduce a nasty colour cast. It works best if you can find a mid-tone gray somewhere.

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Technically, white/black point correction is a completely different thing (ie, turning the brightest/darkest levels in your photos to perfect white/black). This is, technically speaking, exactly called White Balance correction, which tries to correct the tint that the dominant light is sheding (warm orange for a bulb, greenish for fluorescent) or Color Temperature, which your eyes usually adapt to, and hence you do not see with the naked eye. When trying to correct Color Temperature you should point a pixel which does not have any color channel at 255 o 0 values (max o min values), you should rather point a pixel which you think should be grey between mid gray and full white instead of yellowish of blueish. If you choose a full white one, iPhoto cannot compare how each channel is biased from another and thus chooses a default (high) color temperature, which is NOT what you want.

This way of correcting photos is actually commonly done professionally, provided that you carry a small card which is proven 100% perfect neutral gray. That way you photograph the card in the same context as you will make the rest of your photos, correct that photo later on, and apply the same correction to the rest of the photos which do not have a neutral gray card photographed.

Rob, you should change the title of the hint to read something like "Set White Balance correction in iPhoto 5 with point and click".

PS: I actually just implied this from the hint's text, since I do not have iPhoto 5 ^_^

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To those new to this "white balance" concept, here http://www.whibal.com they sell a "neutral gray card", and there you can see how and what one of those is for, and how it is used in professional photo editing software. Usually you can only accurately correct white balance on photographs in RAW format, not JPEG or other. I do not know about what iPhoto 5 does or how accurate its corrections are, though, since as I said, I do not have it.

You can see a live demo of its use at http://rawworkflow.com/WhiBalManual/index.html

I am not related to that guy in any way, BTW.

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(This was sent in as an anonymous hint, but I think it works better as a comment to the original. -rob.)

In revisiting a previous hint on holding down the command-key while clicking on a white part of an image, in Edit mode, to automatically balance the color, I found that in iPhoto 6, you will get more consistent results if you do the command-click on a black part of the image. Even then I had inconsistent results which I then corrected manually or selected another black point. The original hint (for iPhoto 5) rarely worked using a white point. So, in this case, black is better.

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