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Author Topic: White Balance Tool  (Read 3432 times)

BradSmith

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White Balance Tool
« on: October 07, 2011, 09:45:02 PM »

It seems that the tool choses a single pixel to sample for white balance.  Is there a way, as there is in Photoshop, to enlarge the sample area to, say, 5x5 pixels or 10x10?
thanks,
Brad
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David Sutton

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Re: White Balance Tool
« Reply #1 on: October 07, 2011, 10:50:51 PM »

Make sure the toolbar is showing (T key). Tick the “Show Loop” box and then adjust the scale slider to select the sample grid pixel size.
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elied

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Re: White Balance Tool
« Reply #2 on: October 08, 2011, 06:09:17 PM »

The WB tool uses the average RGB values from a 5x5 pixels sample area. Changing the grid loupe size does not change the sample area which is always 5x5. This is the agreement reached almost 50 posts into this thread:

http://forums.adobe.com/thread/854734?start=0&tstart=0
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David Sutton

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Re: White Balance Tool
« Reply #3 on: October 08, 2011, 07:57:09 PM »

Read the thread. More folks shouting at each other.
The Lightroom help file doesn't seem to be much use here. I wish it was sometimes more detailed.
I tried setting the slider to a 5x5 grid and sampled the white balance in an image. Then I set the slider to the maximum grid pixel number and re-sampled the exact same spot on the image. The white balance was significantly different. Try this yourself.
Unless there is something else going on it appears that dragging the slider to the right increases the number of sampled pixels and may be useful when, for example, sampling a noisy image.
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elied

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Re: White Balance Tool
« Reply #4 on: October 09, 2011, 05:26:34 AM »

I have just performed this test: The image below has a 10x10 pixel green square in the middle, surrounded by a 20x20 blue square. When the WB grid is set to 5x5 and centered on the image it shows, of course, only 25 green pixels. When the grid loupe is enlarged to its maximum, 17x17 (289 pixels) and centered it shows 100 green pixels and 189 blue pixels. However, in both cases the WB set is absolutely the same, which demonstrates that the WB is calculated only from the central 25 pixels no matter the grid size.
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David Sutton

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Re: White Balance Tool
« Reply #5 on: October 09, 2011, 06:12:34 AM »

I have just performed this test: The image below has a 10x10 pixel green square in the middle, surrounded by a 20x20 blue square. When the WB grid is set to 5x5 and centered on the image it shows, of course, only 25 green pixels. When the grid loupe is enlarged to its maximum, 17x17 (289 pixels) and centered it shows 100 green pixels and 189 blue pixels. However, in both cases the WB set is absolutely the same, which demonstrates that the WB is calculated only from the central 25 pixels no matter the grid size.

Yes it does! My mistake was not to do my original test at 11:1 in LR. Went back to the original file and sampled at the pixel level and indeed there was no difference between the slider settings.
So, back to the OP's question, does this mean to set a different sample area it has to go to Photoshop?
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hjulenissen

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Re: White Balance Tool
« Reply #6 on: October 09, 2011, 07:14:43 AM »

If you need a larger averaging window, would it be possible to take 2-4 point readings (wiggling the pointer a wee bit in-between), and then manually averaging the results?

A bit inconvenient, but so is exporting to Photoshop..

Seems that Adobe _could_ let you "click and hold while moving the mouse to define a rectangle" as an extension to the existing "click to define a spot" without messing up the user experience/complexity for those that does not need this functionality.

-h
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BradSmith

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Re: White Balance Tool
« Reply #7 on: October 10, 2011, 10:09:53 PM »

Thanks everyone for the info.  I learned something. 

Guess we're stuck with one sample size, 5x5 unless we do multiple samples and average the results.
Brad
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BartvanderWolf

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Re: White Balance Tool
« Reply #8 on: October 11, 2011, 10:19:51 AM »

Thanks everyone for the info.  I learned something. 

Guess we're stuck with one sample size, 5x5 unless we do multiple samples and average the results.

Hi Brad,

Does zooming out change anything? I'm not a frequent Lightroom user, but I remember something that had to do with the screen pixels/zoom. Maybe it changed with recent versions?

Cheers,
Bart
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BradSmith

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Re: White Balance Tool
« Reply #9 on: October 13, 2011, 11:36:09 AM »

Bart,
It seems from the tests done by the guys above, that no matter what the zoom level, it is 5x5.
Brad
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madmanchan

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Re: White Balance Tool
« Reply #10 on: October 14, 2011, 05:03:56 PM »

It is currently always 5x5 average in Lightroom 3.  There will likely be improvements in the future.
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