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Author Topic: No way to balance color with R,G,B points?  (Read 8346 times)
walter.sk
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« on: November 25, 2012, 03:15:58 PM »
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Sorry if my Subject Line above doesn't describe what I'm trying to say, but here it is:

In Photoshop, one of my favorite techniques, even if seldom used, is to color-balance in Levels, using each color channel in conjunction with the Alt key to show me the darkest and lightest pixels in each channel.  So far, I have found no way to do that in LR.  I tried Curves, using the R, G and B curves but the Alt key has no effect.  Dragging the endpoints of the curve in each channel seems too crude to use without seeing the brightest or darkest pixels.

Dragging the ends of the histogram works with the Alt key, but of course you can't adjust individual channels there.

Is there any way to accomplish this in LR?  And if not, is there anything about LR structure that would prevent this technique from being written into the program?  And if not, maybe some kind of simulation of it?
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Tim Lookingbill
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« Reply #1 on: November 25, 2012, 11:04:58 PM »
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Have you tried holding down the Alt key with the Black Point or Exposure slider?

It works for me in ACR with preview indicators similar to Levels.
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walter.sk
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« Reply #2 on: November 26, 2012, 02:10:52 PM »
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Have you tried holding down the Alt key with the Black Point or Exposure slider?

That works well, but not for color balancing, which works by adjusting the end-points of the individual R, G and B channels separately.  The closest I can come in LR or ACR is to go to Curves, select the individual color curves, and try by eye to move the endpoints of the curve to just meet where the data seems to start.  However, it is no as accurate as it would be if holding the Alt key would let me see the darkest and brightest pixels in each channel.
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Scott Hargis
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« Reply #3 on: November 26, 2012, 11:32:38 PM »
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Walter, I'm right there with you. The ability to set a true black point in LR would be WONDERFUL.
You use Levels; I normally accomplish this in Photoshop using a Threshold adjustment layer to identify the black/white points, and then a Curves adjustment layer to eyedropper them - colors and contrast across all tones "snap" into place.
I have a lot of images that would never need to leave LR if I could get this done on a RAW file.
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Schewe
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« Reply #4 on: November 27, 2012, 12:00:15 AM »
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Walter, I'm right there with you. The ability to set a true black point in LR would be WONDERFUL.

No, actually, what you think you want you really don't want. Two entirely different tool sets and workflows.

It would do you guys well to forget and ignore what you do in Photoshop VS ACR/LR. Why? Because in Photoshop you have already committed to a gamma encoded color space. In ACR/LR you are dealing with raw images in a linear gamma and in the camera's native, undefined color space. That's a really big friggin' difference in tool sets.

You may wish you could use techniques you've found that may work in Photoshop, but you are spitting into the wind...it ain't gonna happen and your only option is to learn how to use ACR/LR...then do the stuff that can't be done there in Photoshop. The more you learn to do in ACR/LR, the better your images will be (and the less time you spend diddling images in Photoshop).

Seriously, break the bond between Photoshop tools and ACR/LR tools...it'll only hold you back.
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BartvanderWolf
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« Reply #5 on: November 27, 2012, 04:01:58 AM »
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No, actually, what you think you want you really don't want. Two entirely different tool sets and workflows.

It would do you guys well to forget and ignore what you do in Photoshop VS ACR/LR. Why? Because in Photoshop you have already committed to a gamma encoded color space. In ACR/LR you are dealing with raw images in a linear gamma and in the camera's native, undefined color space. That's a really big friggin' difference in tool sets.

You may wish you could use techniques you've found that may work in Photoshop, but you are spitting into the wind...it ain't gonna happen and your only option is to learn how to use ACR/LR...then do the stuff that can't be done there in Photoshop. The more you learn to do in ACR/LR, the better your images will be (and the less time you spend diddling images in Photoshop).

Seriously, break the bond between Photoshop tools and ACR/LR tools...it'll only hold you back.

Hi Jeff,

While I agree that one should be careful and not try to mimick Photoshop controls in Lightroom, the comparison between ACR and LR functionality where both are using e.g. Process 2012 is tempting. Sure, LR offers some controls that are not found in ACR, but that's because ACR can in principle relay those activities (and more) to Photoshop itself. However, the ACR Tonecurve panel has a Point tab next to the Parametric tab, and that Point tab does allow to do per channel Black point adjustments.

Obviously, that ACR Point tab functionality will only kick in after the actual Raw conversion because it needs RGB rendered image data to work on, but that doesn't mean that LR could not do something similar, like in its very useful Softproofing mode which works with RGB data, when creating the exported output.

Cheers,
Bart
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Vladimirovich
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« Reply #6 on: November 27, 2012, 09:08:15 AM »
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In ACR/LR you are dealing with raw images in a linear gamma and in the camera's native, undefined color space.
no, you are not... when you work with UI (except probably changing things like "process" and "camera profile") you are not dealing with raw data in ACR/LR, you are dealing with something that was demosaicked and color transformed into a defined color space just w/ linear gamma.
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Scott Hargis
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« Reply #7 on: November 27, 2012, 09:26:59 AM »
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Jeff, thanks for chiming in. I'm reading The Digital Negative now, with Real-World Sharpening waiting just behind it.

I would say that what I'm really after is the RESULT, more than the technique for getting there. But I don't know how to describe it except as it relates to the Photoshop Curves method I described.

Is there a recommended way to identify a black point and then set the R,B,G curves to it? Nothing I know how to do in LR gets me the same result.
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digitaldog
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« Reply #8 on: November 27, 2012, 09:35:19 AM »
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no, you are not... when you work with UI (except probably changing things like "process" and "camera profile") you are not dealing with raw data in ACR/LR, you are dealing with something that was demosaicked and color transformed into a defined color space just w/ linear gamma.

No, Jeff's correct. You are presented with a "gamma" corrected preview (actually not a gamma curve but the sRGB TRC), the data is always processed as Jeff describes.
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Andrew Rodney
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Vladimirovich
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« Reply #9 on: November 27, 2012, 10:09:23 AM »
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No, Jeff's correct. You are presented with a "gamma" corrected preview (actually not a gamma curve but the sRGB TRC), the data is always processed as Jeff describes.


ACR/LR do not operate on raw data (be it RGBG or CMYG or Foveon or whatever) data UI wise... all sliders that you are moving in UI are instructions of what shall be done with the data that was already 1) demosaicked and 2) transformed to a color space with prophoto coordinates and linear gamma... why do you want to argue w/ that ?

the only time when ACR/LR does redemosaicking and color transform of the data from "camera's native, undefined color space." to a defined, internal working spaces (where the raw conversion actually ends) is when you change the process and/or dcp camera profile... that is the core of what Adobe calls "dng processing model" that makes its UI close to real time speedwise, exactly because you do not operate with raw data.

PS: I hope Jeff explains this in his book and not misrepresents the situation.
« Last Edit: November 27, 2012, 10:15:02 AM by Vladimirovich » Logged
RFPhotography
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« Reply #10 on: November 27, 2012, 10:10:04 AM »
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Hi Jeff,

While I agree that one should be careful and not try to mimick Photoshop controls in Lightroom, the comparison between ACR and LR functionality where both are using e.g. Process 2012 is tempting. Sure, LR offers some controls that are not found in ACR, but that's because ACR can in principle relay those activities (and more) to Photoshop itself. However, the ACR Tonecurve panel has a Point tab next to the Parametric tab, and that Point tab does allow to do per channel Black point adjustments.

Obviously, that ACR Point tab functionality will only kick in after the actual Raw conversion because it needs RGB rendered image data to work on, but that doesn't mean that LR could not do something similar, like in its very useful Softproofing mode which works with RGB data, when creating the exported output.

Cheers,
Bart

You have this in LR 4.x with PV2012 as well though, right?  In PV2012, the Tone Curve panel allows you to, when using the Point Curve, select the composite RGB or any of the individual channels.
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Schewe
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« Reply #11 on: November 27, 2012, 10:48:41 AM »
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ACR/LR do not operate on raw data (be it RGBG or CMYG or Foveon or whatever) data UI wise... all sliders that you are moving in UI are instructions of what shall be done with the data that was already 1) demosaicked and 2) transformed to a color space with prophoto coordinates and linear gamma... why do you want to argue w/ that ?

For the purposes of displaying an image preview, yes...ACR/LR is showing you a "preview" of what the raw data "will" look like for the purposes of adjustment, but nothing has been done to the raw data processing pipeline until you actually process the image. Then ACR/LR (export or open in PS) will demosiac the raw data, transform from camera color, run the image through the raw processing pipeline, then do the final gamma encoded color space transform. So, of course, ACR/LR operate on the raw data...all of the adjustments are done to a preview of the raw data...but sure what your argument is?
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digitaldog
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« Reply #12 on: November 27, 2012, 11:44:05 AM »
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ACR/LR do not operate on raw data (be it RGBG or CMYG or Foveon or whatever) data UI wise... all sliders that you are moving in UI are instructions of what shall be done with the data that was already 1) demosaicked and 2) transformed to a color space with prophoto coordinates and linear gamma... why do you want to argue w/ that ?

It's not working on the raw data? What's it working on?

The preview is just that, a preview. The raw is just that, raw. You're simply creating instructions along with the preview and at some point raw data to produce RGB data from an engine that works with linear encoded data (even if you feed it a rendered gamma corrected image). That doesn’t happen until you export the data or send it though a module (make me a web gallery).

Quote
the only time when ACR/LR does redemosaicking and color transform of the data from "camera's native, undefined color space." to a defined, internal working spaces (where the raw conversion actually ends) is when you change the process and/or dcp camera profile...

So what's happening when I move a slider? What happens when I export a web gallery or print the image? It sure isn't using the preview (unless I ask to print in Draft mode).
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Andrew Rodney
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BartvanderWolf
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« Reply #13 on: November 27, 2012, 12:34:09 PM »
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You have this in LR 4.x with PV2012 as well though, right?  In PV2012, the Tone Curve panel allows you to, when using the Point Curve, select the composite RGB or any of the individual channels.

Hi Bob,

You are correct, my bad. I overlooked the small icon at the bottom of the Tonecurve palette which after clicking it hides the region sliders and displays a channel selector when you click on the RGB acronym. Then the individual Black points can be adjusted per channel, just like the OP wants (except for the Alt/Option preview). So then the question becomes; Why no preview?

Cheers,
Bart
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RFPhotography
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« Reply #14 on: November 27, 2012, 01:07:18 PM »
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If you turn on the clip warnings on the histogram, does that do it?
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walter.sk
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« Reply #15 on: November 27, 2012, 01:27:46 PM »
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I overlooked the small icon at the bottom of the Tonecurve palette which after clicking it hides the region sliders and displays a channel selector when you click on the RGB acronym. Then the individual Black points can be adjusted per channel, just like the OP wants (except for the Alt/Option preview). So then the question becomes; Why no preview?
You understand my question.  While I get lost in the heady level of discussion at the technical level, my naive thinking says to me that whether or not the per channel adjustments are actual or just simulated in a preview, it does seem to me that the Alt/Option preview should not be impossible in LR, and I would find it helpful.  I am getting better at adjusting each channel's black point and white point by dragging the end point of each channel's curve, which I find *much* more accurate and efficient than clicking around with the eyedropper looking for something that is supposed to be neutral in the image, in the White Balance part of the basic panel. (I know I should shoot a gray card in the field, but that doesn't always happen.)
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BartvanderWolf
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« Reply #16 on: November 27, 2012, 01:47:48 PM »
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If you turn on the clip warnings on the histogram, does that do it?

Yes, in a way, but only for the clipped levels (no info on the proximity to the clipping point, so one needs to slide back and forth for an impression). Maybe it's close enough for Walter's use.

Cheers,
Bart
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RFPhotography
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« Reply #17 on: November 27, 2012, 03:04:30 PM »
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I don't find that the Alt method with Levels in PS works much differently.  It overlays a mask and shows clipped pixels.  Unless I'm missing something.  The thing I'm not sure of in LR is whether the clipping warnings pertain to each channel when in that mode of the Tone Curve module or are still overall RGB clipping.
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Vladimirovich
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« Reply #18 on: November 27, 2012, 04:17:14 PM »
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It's not working on the raw data? What's it working on?

ACR/LR are 2 in 1

1) a raw converter hidden from you (almost, again - you can select the process version and dcp profile) that reads the data, does whatever normalization you need, does demosaick, does color transform and the pass the result to next component with which you actually interact, thinking that you work with raw data

and

2) a version of PS designed to work with images originating from that hidden raw converter - that is what exposed to you through UI, where you do "WB", "exposure compensation" and so on... but you do not do this with the raw data... and hence you can actually do this in a proper raster image editor, the mere fact that PS is lacking something that is present in ACR/LR does not change that fact.


The preview is just that, a preview. The raw is just that, raw. You're simply creating instructions along with the preview and at some point raw data to produce RGB data from an engine that works with linear encoded data (even if you feed it a rendered gamma corrected image). That doesn’t happen until you export the data or send it though a module (make me a web gallery).

the point is - all of your sliders in ACR/LR UI do not work operate on raw data... the mere fact that working color space is linear encoded does not make it raw data - you can as well get that to PS and work there (yes, not convenient)

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Vladimirovich
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« Reply #19 on: November 27, 2012, 04:23:18 PM »
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So, of course, ACR/LR operate on the raw data

operations that you control through UI (except process version and camera profile selected) in ACR/LR do not operate on raw data

...all of the adjustments are done to a preview of the raw data

no - all adjustments are done on demosaicked and color transformed data, you can't call that raw data... if I do something before demosaick then I can say that I operate with raw data, but none of ACR/LR UI sliders or curves do that... not even white balance.

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