11 Replies Latest reply on Jan 7, 2016 2:09 PM by Todd Shaner

# Average luminosity of an area

I like to optimise the appearance of faces on fotos placed in rooms with a non-optimal light.

I like to have an averaged value of an area, like a face, for that.

I have seen that I can get the RGB value of pixels. That is not bad. But I would rather have those values from an user defined area and also summed up values.

Is there a way to do that? I would then make a virtual copy of a foto and push the brightness before printing.

• ###### 1. Re: Average luminosity of an area

Hi,

Lightroom Tone Curve has a small button on the upper left corner which allows adjusting by dragging up and down using the mouse. When used, this tool shows two figures: original and adjusted brightness %.

Here, the area under my pointer has an original brightness of 62% adjusted to 64% (as shown by the curve shape).

To create the virtual copy of the Photo, right-click on the image and choose create virtual copy.

Thanks

• ###### 2. Re: Average luminosity of an area

Hi,

thanks a lot. The area under the pointer - how big is that? Can I adjust that area?

• ###### 3. Re: Average luminosity of an area

So I answer my own question:

In LR I can crop an area. The histogram will then only show that area. But LR does not produce average values for the channels or any other statistic. Same us true for the tone curve.

In PS, I can also make the histogram to show a cropped area. However, in PS, the histogram shows all kinds of statistics,  just what I was looking for! So, to do what I want, I need to export to PS, meter there and then... Well not quite sure. Either adjust in PS or do it in LR until it us Ok. Statistics for the LR histogram would be a nice feature...

I also toyed with WB. I get a 5x5 matrix which I can make to cover a face by zooming out. But then I only see relative % of RGB values which is if no help.

• ###### 4. Re: Average luminosity of an area

joachims25232702 wrote:

I also toyed with WB. I get a 5x5 matrix which I can make to cover a face by zooming out. But then I only see relative % of RGB values which is if no help.

Turn on Soft Proof with Profile set to ProPhoto RGB for LR's native color space or choose a target color profile. The Histogram RGB readings will then be 0-255 8-bit readings. The White Balance Eyedropper tool will show you the "average" RGB reading of the area being sampled (5x5 up to 17x17 pixels @ 1:1 Zoom View). You can further adjust the sample size by changing the Zoom View setting.

• ###### 5. Re: Average luminosity of an area

Thanks. That is good, but I rather wanted to see the "luminosity" of an area and hence the absolute RGB values. Using WB would have just been an example how I believe the histogram pipette should work (with averaged values too...)

• ###### 6. Re: Average luminosity of an area

To see the Luminosity value you can change the Histogram to show 'Lab Color Values' instead of RGB % values. No Soft Proof required.

• ###### 7. Re: Average luminosity of an area

...but that is then not an average value for an area, is it? Not even for a cropped region? (not like in PS)

• ###### 8. Re: Average luminosity of an area

The White Balance Eyedropper tool provides the 'Average Value' of the selected area. I suggested this capability be implemented over 5 years ago and it was implemented in LR4.

Lightroom: Add options for larger sample sizes for White Balance Eyedropper Tool

The primary difference between the LR and PS's Eyedropper tool is that the sample size varies dependent on Zoom View setting in LR. In PS it is a "fixed" sample area dependent only in the selected 'Sample Size.'

I just tested the LR CC 2015.3 WB Eyedropper and only appears to work as expected (i.e. Average reading) with 5x5 Scale setting at 1:1 Zoom View and higher (2:1, etc.). I'll be reporting this as a bug at the above link.

• ###### 9. Re: Average luminosity of an area

Hi Trshaner,

we are almost there. So, yes, I see what probably is the averaged LAB value for the 5*5 area. That is good. Whatt is LAB, sorry for the dumb question? Does it relate to absolute luminosity?

A bit of background: I like to measure the average "brightness" of a faces to be able to produce prints that I can adjust so the look pleasant in a 50 lux living room. I can pretty much establish a "calibration" by looking at how prints came out in the past. I also opened another thread for that purpose where I ask it an ICC profile could be tweaked to do a similar thing: make the softproof look like a photo illuminated with 50lux and then adjust brightness.

Thanks

• ###### 10. Re: Average luminosity of an area

joachims25232702 wrote:

we are almost there. So, yes, I see what probably is the averaged LAB value for the 5*5 area. That is good. Whatt is LAB, sorry for the dumb question? Does it relate to absolute luminosity?

L = Luminosity or Brightness.

"The red/green opponent colors are represented along the a* axis, with green at negative a* values and red at positive a* values. The yellow/blue opponent colors are represented along the b* axis, with blue at negative b* values and yellow at positive b* values."

Lab color space - Wikipedia, the free encyclopedia

You can use the L value to determine the absolute brightness independent of skin color. Since the color component and Luminosity component are separate readings you can also check skin color independent of light level using the 'a' and 'b' readings.

I just remembered there is also a bug with LR Soft Proof RGB readings. The below bug report is marked 'In Progress' so hopefully this will be corrected in the next update (6.4). Fortunately, the Lab values in the Develop module are correct and should work fine for your purpose.

Lightroom CC: Soft Proof Histogram Displays Incorrect RGB Values

• ###### 11. Re: Average luminosity of an area

Here's the problem report for the LR WB Eyedropper tool sample area issue:

Lightroom White Balance Eyedropper Tool No longer Working Properly