White Balance in Lightroom vs in Photoshop

From what I understand, you can get a precise white balance in Lightroom by using the eyedropper tool to find a neutral grey color in a photo, but how can you tell for sure that what you choose is actually natural grey? it's very subjective...
Also, I've read in an article on the web that all you have to do is find an area in a photo where all three RGB colors have exactly the same value, and get a natural color. But, in order to get a natural GREY color all the values must be 128, right? pretty confusing...

And, how is using this eyedropper tool compared to using threshold in Photoshop to get a precise white balance?

TIA

As long as all three channels should have the same value you should be able to use the WB eye dropper to set the correct value in both LR or ACR. If the point you sample is very dark then the result could be skewed by noise, so I would want to be using brightness values above around 25% in LR, which would equate to 64,64,64 in an 8 bit scale. Another issue that you can bump into with very bright values is that you may just run into clipping of one channel so it is usually good to stay under 90% or so. In this case though you do get warning that the WB cannot be set. Picking the correct colour to WB from is a matter of experience. You either include a grey card target in the fame for setting the WB or you have t know that the target you pick should be pure white/grey.

I would not be trying to reset the WB of an image using the tools in PS. If I needed to adjust the WB I would be doing that in my RAW converter, as I use Adobe tools that would either be LR (which I use) or ACR, which is provided with PS. Concurrent versions of LR/ACR both have IDENTICAL toolsets, so it doesn't really matter which one you use. I do though shoot everything in RAW. On the odd occasion that I have to deal with WB correcting RGB images such as TIFF or JPEG I would open them in either LR or ACR too. Both programs can work with RGB formats as well as with RAWs.

The channel values of a grey target can be anything you like, as long as they are all the same. 128,128,128 is only significant as it is the middle value for grey. If you use an 18% grey card for setting exposure then the values for "correct" exposure will be 128, 128, 128. It is important to remember that the "correct" exposure may not always be the right exposure to use depending on the subject, and the resulting image that you may be trying to achive.

Alan

No Al, 18% grey is not the exact center of the tonal range. In sRGB space it is around 118 on the 0-255 scale and a bit less in Adobe RGB, around 117. 18% was chosen by Ansel Adams as the standard for film development (despite opposition from Kodak engineers) apparently because it produced a negative density in the middle of the H.D. Curve with good shadow and highlight detail when properly developed. Today, however, digital camera meters are calibrated in the 12-13% range, around 100-103 in the 8 bit scale.

rfe777, you need to understand that "grey" is any shade from black to white, so long as the three color components are equal. When using the eyedropper you can only be sure the WB is absolutely accurate only if you have inserted into the scene a grey card that is known to be neutral, but complete accuracy is generally not needed, human color perception isn't that good, and it is often more important to go for a pleasing or expressive coloration rather than pure accuracy.

In Photoshop you can use a Threshold adjustment layer to find the exact grey point in an image (assuming one exists). Its a technique developed by Dave Cross and it is described here: Dave's Amazing Trick for Finding a Neutral Gray

You can also use a Threshold adjustment layer to find the black and white points of an image, then use a Levels or Curves adjustment layer to also make them equal.

rfe777 wrote in post #16853591
From what I understand, you can get a precise white balance in Lightroom by using the eyedropper tool to find a neutral grey color in a photo, but how can you tell for sure that what you choose is actually natural grey? it's very subjective...
Also, I've read in an article on the web that all you have to do is find an area in a photo where all three RGB colors have exactly the same value, and get a natural color. But, in order to get a natural GREY color all the values must be 128, right? pretty confusing...

And, how is using this eyedropper tool compared to using threshold in Photoshop to get a precise white balance?

TIA

PixelMagic, that's an interesting technique, handy to know if we just can't "nail" it in Camera Raw/Lightroom, thanks for sharing that!

PixelMagic wrote in post #16853803
In Photoshop you can use a Threshold adjustment layer to find the exact grey point in an image (assuming one exists). Its a technique developed by Dave Cross and it is described here: Dave's Amazing Trick for Finding a Neutral Gray

You can also use a Threshold adjustment layer to find the black and white points of an image, then use a Levels or Curves adjustment layer to also make them equal.

I recall seeing this in a Kelby book somewhere, but had lost track of it. Thanks for the refresher! In fact, now that I look at the link, I'm pretty sure it was one of the Kelby books on Elements. Perhaps version 8?

rfe777 wrote in post #16853591
From what I understand, you can get a precise white balance

All these techniques will get you an accurate colour balance. Which is often a good starting point for the correct colour balance.

Thank you all for your replies.

However, I do feel that that with Photoshop you can get the most precise white balance. Lightroom and ACR seem to do a more general editing, while Photoshop does a "surgical" one...

Or maybe I'm wrong?

tzalman wrote in post #16853789
No Al, 18% grey is not the exact center of the tonal range. In sRGB space it is around 118 on the 0-255 scale and a bit less in Adobe RGB, around 117. 18% was chosen by Ansel Adams as the standard for film development (despite opposition from Kodak engineers) apparently because it produced a negative density in the middle of the H.D. Curve with good shadow and highlight detail when properly developed. Today, however, digital camera meters are calibrated in the 12-13% range, around 100-103 in the 8 bit scale.

rfe777, you need to understand that "grey" is any shade from black to white, so long as the three color components are equal. When using the eyedropper you can only be sure the WB is absolutely accurate only if you have inserted into the scene a grey card that is known to be neutral, but complete accuracy is generally not needed, human color perception isn't that good, and it is often more important to go for a pleasing or expressive coloration rather than pure accuracy.

That's interesting. Maybe that explains why Datacolor suggests to use the second patch from white in their SpyderCheckr chart for WB, instead of the more 'greyish' ones.

rfe777 wrote in post #16855809
Thank you all for your replies.

However, I do feel that that with Photoshop you can get the most precise white balance. Lightroom and ACR seem to do a more general editing, while Photoshop does a "surgical" one...

Or maybe I'm wrong?

Well, no surprise that PS has tools that you could call more "surgical", it's just a question of what is the best approach for you and the photography you do!

For me, Lightroom handles things nicely with my Raw workflow. If I need "surgery", sure, I can take the time to go into Photoshop..."Nurse, come and assist!"

rfe777 wrote in post #16855809
Thank you all for your replies.

However, I do feel that that with Photoshop you can get the most precise white balance. Lightroom and ACR seem to do a more general editing, while Photoshop does a "surgical" one...

Or maybe I'm wrong?

You're wrong (IMHO). By the time you get the image to PS - no photograph gets to PS without first having started life as a Raw and having passed through a converter - it has already had a WB applied to it. PS can only change an already existing situation by doing WB #2 on top of the first, the one done during conversion from Raw to RGB. LR or ACR work on a tabula rasa, which gives them both greater latitude and greater precision.

tzalman wrote in post #16856629
You're wrong (IMHO). By the time you get the image to PS - no photograph gets to PS without first having started life as a Raw and having passed through a converter - it has already had a WB applied to it. PS can only change an already existing situation by doing WB #2 on top of the first, the one done during conversion from Raw to RGB. LR or ACR work on a tabula rasa, which gives them both greater latitude and greater precision.

Yeah, like Elie says!

rfe777 wrote in post #16853591
From what I understand, you can get a precise white balance in Lightroom by using the eyedropper tool to find a neutral grey color in a photo, but how can you tell for sure that what you choose is actually natural grey? it's very subjective...
Also, I've read in an article on the web that all you have to do is find an area in a photo where all three RGB colors have exactly the same value, and get a natural color. But, in order to get a natural GREY color all the values must be 128, right? pretty confusing...

And, how is using this eyedropper tool compared to using threshold in Photoshop to get a precise white balance?

TIA

If all three RGB channels have the same values then that item should already be grey/white/black and using the eyedropper on it won't get you any change.

I just started using a grey card for white balance. Using the presets from LR is a good start but I find using the grey card isn't far off from the auto WB in LR, most of the time.

In my opinion the latter part of your comment regarding "greater precision" needs qualifying. If there's a spectrally neutral grey card used as a reference in the photo there shouldn't be any difference between WB in the raw converter (LR or Adobe Camera Raw) and Photoshop.

However, if a grey reference is not used Photoshop can provide a more accurate white balance since you can use tools like a Threshold adjustment layer, the Info panel, and Curves adjustment layer to precisely identify neutral grey areas in a photo and adjust it accordingly. On the other hand, with Lightroom/ACR its a guessing game to find out where the actual grey point is in an image unless you send it to Photoshop as a Smart Object, identify the area, then go back into the raw converter to click on the grey point.

Also, Photoshop has another advantage of allowing color correction "by the numbers." Once that's understood you can do adjustments on an uncalibrated monitor with confidence that those adjustments are accurate.

tzalman wrote in post #16856629
You're wrong (IMHO). By the time you get the image to PS - no photograph gets to PS without first having started life as a Raw and having passed through a converter - it has already had a WB applied to it. PS can only change an already existing situation by doing WB #2 on top of the first, the one done during conversion from Raw to RGB. LR or ACR work on a tabula rasa, which gives them both greater latitude and greater precision.