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Author Topic: Can You Change the Sample Size of the Sampling Cursor  (Read 458 times)

BradSmith

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Can You Change the Sample Size of the Sampling Cursor
« on: January 19, 2019, 07:14:55 pm »

I would like to be able to vary the sample size of the cursor when I'm checking LAB values under the histogram in Develop Mode.  Can this be done?  I can't find a way to do it.  Anyone know how large the sample size is?
Brad
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Mark D Segal

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Re: Can You Change the Sample Size of the Sampling Cursor
« Reply #1 on: January 19, 2019, 07:23:30 pm »

In the lower right of the GUI, make sure Show Loupe is active, then slide the slider to the right to include more pixels used when sampling a white balance adjustment. See figure.
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Mark D Segal (formerly MarkDS)
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BradSmith

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Re: Can You Change the Sample Size of the Sampling Cursor
« Reply #2 on: January 19, 2019, 09:01:03 pm »

Might be a LR Version issue.  I'm using LR Classic CC, release 7.5.    You said on the lower right of the GUI, but the number selected and file name are on the lower left of my screen.  I assume you meant lower left.  But in that location, I don't see what your screen is displaying.  Here is mine
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Mark D Segal

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Re: Can You Change the Sample Size of the Sampling Cursor
« Reply #3 on: January 19, 2019, 09:20:16 pm »

Yes, sorry, lower left; I'm using Lightroom Classic version 7.1. You need to select the white balance tool before that little menu appears.
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Mark D Segal (formerly MarkDS)
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digitaldog

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Re: Can You Change the Sample Size of the Sampling Cursor
« Reply #4 on: January 19, 2019, 10:17:51 pm »


Color samplers used a zoom-independent sampling such you can zoom in and out and the values should not change. But WB is zoom level dependent. So if you want to average over a larger area, zoom out.

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Andrew Rodney
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digitaldog

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Re: Can You Change the Sample Size of the Sampling Cursor
« Reply #5 on: January 19, 2019, 10:49:32 pm »

Here's the issue with changing grid size: Nothing changes in terms of the values:
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Andrew Rodney
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Mark D Segal

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Re: Can You Change the Sample Size of the Sampling Cursor
« Reply #6 on: January 19, 2019, 10:50:11 pm »

Andrew, for White Balance, I assume you mean the same thing that Martin Evening says on page 175 of his Lightroom 6 book: ""You can adjust the loupe scale setting by dragging the slider next to the Show Loupe item in the Toolbar. ..........and dragging the slider to the right increases the number of pixels used when sampling a white balance point measurement."
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Mark D Segal (formerly MarkDS)
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Mark D Segal

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Re: Can You Change the Sample Size of the Sampling Cursor
« Reply #7 on: January 19, 2019, 10:54:48 pm »

Here's the issue with changing grid size: Nothing changes in terms of the values:

In your illustration it looks like a one pixel measurement right in the center, so whether the portrayal of that same pixel is large or small it's the same pixel and will have the same value. Martin clearly states at the bottom of page 175 that the White Balance sample is zoom-level dependent. If that's the case then it would seem you are not talking about white balance?
(edit for removing typo)
« Last Edit: January 20, 2019, 09:45:12 am by Mark D Segal »
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Mark D Segal (formerly MarkDS)
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digitaldog

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Re: Can You Change the Sample Size of the Sampling Cursor
« Reply #8 on: January 19, 2019, 11:04:10 pm »

Not all pixels are identical and there are a few magenta and green pixels but identical Lab values which is screwy.
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Andrew Rodney
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BradSmith

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Re: Can You Change the Sample Size of the Sampling Cursor
« Reply #9 on: January 20, 2019, 01:34:27 am »

Mark, Andrew;
In playing with it, I noticed that the Scale slider that you mentioned seemed to be just a magnifying glass showing fewer or more pixels, and seemed to have no effect on the actual sampling size.  Yet you quote Martin Evening as saying the sample size is dependent on the Scale.  So to verify this, I decided to test the sensitivity of the cursor position to see if I could figure out how big the sampling size was, and if it was different depending on the Scale. 

In Photoshop, I created a 30 pixel per side square in black.  Then added a white 5x5 box in the center.  Imported it into LR.   In the Develop Module, I Zoomed up to 11x1 magnification, selected the WB tool, turned on "Show Loupe" and moved the Scale slider all the way to the left (greatest loupe magnification) and started moving the sampling tip across the box, watching the lab values and RGB values as I progressed, pixel by pixel.  In the center pixel in the white box, L and RGB=100. That must mean that the sample can't be bigger than 5x5 (but could be smaller).  Then I slid the cursor point into the adjacent pixel,  and the L value dropped. That means it IS 5x5.   It kept incrementally dropping when I moved into the next pixel till I had moved it five pixels right or left, up or down. L and RGB had dropped to zero in the 5th pixel. This confirmed that it is 5x5 with the slider all the way to the left.

Then I set the Loupe slider all the way to the right (least magnification) and repeated the test, pixel by pixel.   Exact same results.  5x5 sampling area.   So, my results showed that the size of the sample for the white balance tool is constantly 5x5 no matter what scale you are using in "Show Loupe".  All Show Loupe does is show more or fewer pixels.

I think that 5x5 is a really small sample size and it would be better to be larger and best of all if you could vary its size. 
Brad

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Mark D Segal

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Re: Can You Change the Sample Size of the Sampling Cursor
« Reply #10 on: January 20, 2019, 09:49:30 am »

Yes, when I was playing around with it I had the same impression - the adjustment just changes the number of pixels we see there, not the colour sampling behaviour. Yet there is the quote from Martin who really knows this program, but then your evidence above seeming to indicate that the calculations don't change with the extent of magnification. Deserves further clarification.
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Mark D Segal (formerly MarkDS)
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digitaldog

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Re: Can You Change the Sample Size of the Sampling Cursor
« Reply #11 on: January 20, 2019, 11:02:20 am »

Schewe once wrote:
Pretty sure that White Balance and the Color Sampler are not the same
behavior...Pretty sure White Balance is always 5x5 image pixels while the
Color Sampler is 5x5 screen pixels. As a result, one CAN increase the
accuracy of the color sampler by zooming in beyond 1:1. In the case of White
Balance, I don’t think that’s true...
By zooming in you COULD better determine which 5x5 pixels get factored in
the white balance determination...
For a while, Bruce Fraser (as well as my self) felt that the white balance
tool and the color sampler tool should behave the same...course, Camera Raw
has the ability to add up to 9 color samplers something Lightroom hasn’t
caught up on.


Eric Chan once wrote:
Yes, color samplers used a zoom-independent sampling so that as you zoom in/out the readout values don’t change.
On the other hand, WB is zoom-level-dependent, so if you want to average over a greater area, just zoom out (handy for noisy images) ...

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Andrew Rodney
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Mark D Segal

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Re: Can You Change the Sample Size of the Sampling Cursor
« Reply #12 on: January 20, 2019, 12:03:21 pm »

I read this twice Andrew, and it seems to me that Jeff and Eric aren't saying the same thing about WB behaviour. Am I missing something?
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Mark D Segal (formerly MarkDS)
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digitaldog

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Re: Can You Change the Sample Size of the Sampling Cursor
« Reply #13 on: January 20, 2019, 12:07:54 pm »

Sampling for WB and sampling for the readout's are apparently not the same which is what the OP is asking about.
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Andrew Rodney
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BradSmith

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Re: Can You Change the Sample Size of the Sampling Cursor
« Reply #14 on: January 20, 2019, 12:50:31 pm »

Regarding what you're calling color sampler.....are you referring to the values that show up when you're in the Develop Module and these are the values directly below the curson hand?  If so, I did the same test as the B&W test I did before using the WB tool, but this time with an image that was a 25x25 blue box with a 5x5 red box in the center.  The values displayed below the histogram behaved just like with the WB tool - 5x5 pixel sampling area.

Or more likely, you're referring to the color sampler tool in Develop at the bottom of Adjustment Brush menu.  see attached.  That tool does work differently.  On my blue/red box, when the very tip of the eye dropper crosses the border from 1 actual image blue pixel to the adjacent red image pixel, it value jumps to the appropriate color value.  There is no progression of values.  So it looks like it may be working on reading a very tiny number of screen pixels (maybe 1) rather than actual image pixels.
Brad 
« Last Edit: January 20, 2019, 01:06:40 pm by BradSmith »
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digitaldog

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Re: Can You Change the Sample Size of the Sampling Cursor
« Reply #15 on: January 20, 2019, 12:56:24 pm »

Regarding what you're calling color sampler.....are you referring to the values that show up when you're in the Develop Module and these are the values directly below the curson hand?  If so, I did the same test as the B&W test I did before using the WB tool, but this time with an image that was a 25x25 blue box with a 5x5 red box in the center.  The values displayed below the histogram behaved just like with the WB tool - 5x5 pixel sampling area.
Brad
Yes and yes. Samples for readout AFAIK are always 25 pixels no matter how many appear in the WB overly.
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Andrew Rodney
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