RetouchPRO

Go Back   RetouchPRO > Technique > Photo Retouching
Register Blogs FAQ Site Nav Search Today's Posts Mark Forums Read


Photo Retouching "Improving" photos, post-production, correction, etc.

L*a*b* question: why can't it be simulated in RGB?

Reply
 
Thread Tools
  #31  
Old 09-09-2010, 01:20 PM
Chain's Avatar
Chain Chain is offline
Senior Member
 
Join Date: May 2009
Location: Oslo, Norway
Posts: 551
Arrow Re: L*a*b* question: why can't it be simulated in

Quote:
Originally Posted by andrewrodney View Post
Make a new layer, name it Dodge & Burn, set the mode to Overlay. If you then paint on it with black you burn, paint with white, you dodge.
<offtopic>

Yep, that's a different way of dodging/burning that we haven't addressed in this thread (and I hope we won't, this thread is heavy enough as it is, hehe). I used that technique myself at first, but I've changed to using Curves;
One layer for dodging (a brightening curve), and one for burning (a darkening curve). Then i do my brushing in the mask (using a Wacom tablet, 100% opacity, low Flow setting). What I like about this is I can adjust the curves to get excellent control over how it darkens/brightens the image at any point, and it is easy to do adjustments directly on the mask as well if I need to (e.g. if i realize half way through that I need the dodge layer to be a bit stronger I can increase the curve, and then darken the already painted mask to give me more "room" to work without messing up what I've done so far).

In the examples in this thread I've set the curves layer to blending mode Luminosity to avoid it shifting the hue/saturation, but usually I admit to leaving it set to Normal. The color in the areas that needs to be dodged/burned is usually not the same as the surrounding anyway, so they have to be adjusted - and I can do that afterward if I see the need. When at Normal I can actually adjust the RGB channels individually to manually tweak the color of the dodge/burn, but I usually do this on separate layers for better control. Using one layer as a clipping mask for several other adjustment layers is also a neat little trick (that way several adjustments "share" the same mask).

</offtopic>

Note to self: posting something off-topic on the top of the page is probably not nice for people trying to catch up to the thread... -.-
Reply With Quote top
  #32  
Old 09-09-2010, 01:47 PM
mistermonday's Avatar
mistermonday mistermonday is offline
Moderator
Patron
 
Join Date: Dec 2005
Posts: 3,028
Re: L*a*b* question: why can't it be simulated in

Andrew, a couple of years ago I locked myself away for a long time running benchmarks on some real life Hi Res portrait images trying to improve and short cycle the D&B process. I started with the process you described above but quickly decided that 50% gray layers were the least desirable for me. I tried solid white and black layers masked and set to various blend modes with non linear pixel blending formulae. Created some flters to isolate bands of pixel. Tried using the actual Dodge and Burn tools from the PS tool box (a technique preferred by Amy Dresser). Tried a few unconventional perversions of PS. In the end I found that separate Lighten and Darken curves worked best for me.
Choice of RGB versus LAB is mmade upfront based on how how much unevenness in color already exists in the image, the size and quantity of areas / pixels requiring a reduction in local contrast, and the intensity of the contrast that requires attenuation. I know how to diminish all of those things with good equipment, lighting, and makeup. Unfortunately for those images taken by others, I am at the mercy of poor skill and bad fortune. I work almost exclusively in 16 bit.
When I decide to go with LAB, I do the conversion right up front and stay there until the image is finished. Aside from D&B, fine detail healing is a very important but not a problem as I use Frequency Split layers just as I do in RGB but with some added advantages.
Occasionally I will be half way through a retouch and discover I really need a trip to LAB for something unanticipated. At that point an embedded / nested smart object carried out in LAB color dovetails seamlessly inside that RGB workflow. And I must add conversely that an embedded / nested smart object dovetails equally well inside an all LAB flow.
Regards, Murray
Reply With Quote top
  #33  
Old 09-09-2010, 01:51 PM
mistermonday's Avatar
mistermonday mistermonday is offline
Moderator
Patron
 
Join Date: Dec 2005
Posts: 3,028
Re: L*a*b* question: why can't it be simulated in

Chain, thanks for your latest files. I won't have an opportunity to do much with them until tonight but I will check them out and advise.
Regards, Murray
Reply With Quote top
  #34  
Old 09-09-2010, 02:22 PM
mistermonday's Avatar
mistermonday mistermonday is offline
Moderator
Patron
 
Join Date: Dec 2005
Posts: 3,028
Re: L*a*b* question: why can't it be simulated in

Hi Flashtones, If I decide to use LAB, I go in right after 16 bit capture and open in PS.
Flows vary depending on the image but for a beauty retouch generally like this:
- Macro tone / color adjustment of the image
- Major physical changes such as Liquify to reshape or any structural surgery
- Frequency Split Layer set(s) usually at one or two different radii using Accurate High Pass method to create a conventional split where LF and HF layers have color interdependency or a type of split where the color is completely separated off the HF layer. Lots done on this layer - texture replacement, general healing, some hair work as appropriate, eye veins etc.
- Degrunge layer created with Accurate High Pass and used to attenuate large areas of excessive contrast but low texture. This done as a means of reducing drudgery and time on the D&B layers. But done only if the right conditions in the image are present and if the results do not in any visible way negatively impact the image.
- Dodge Layer
- Burn Layer
- D&B color correction layer
- Light contouring layer, sometimes incorporated in D&B, sometimes separate
- Conditional layers; eyes, hair, teeth, other
- Final color balance if req'd
- Selective sharpening
- Sharpening for output
There are a lot of variables that come into play in different images so order can vary.
Regards, Murray
Reply With Quote top
  #35  
Old 09-09-2010, 02:35 PM
Flashtones Flashtones is online now
Senior Member
 
Join Date: Apr 2009
Posts: 956
Re: L*a*b* question: why can't it be simulated in

Murray, I'd love to watch you work sometime. Please do an RTP live show with Doug!
Reply With Quote top
  #36  
Old 09-09-2010, 04:22 PM
andrewrodney's Avatar
andrewrodney andrewrodney is offline
Senior Member
 
Join Date: May 2010
Location: Santa Fe
Posts: 1,091
Re: L*a*b* question: why can't it be simulated in

Quote:
Originally Posted by mistermonday View Post
Add a dodge curve, dodge the top right corner until the luminosity of it equals the left side iof the image (eyedropper samplers are there). Add a blank layer set to color and paint with the left side color. Turn off the visibility layer.

In a typical D&B on a portrait, the D/B curves shift the saturation as well as the lightness. Trying to color correct is not that easy or quick. You can add a Hue/Sat layer with a layer mask copied from the D/B curve but that has its issues.
Been an insane day so my head is a bit clogged up. I did take a quick look at the two files. Question: Can I assume that the goal is to have that top “Visualize” layer on, and see the upper right quadrant in the RGB doc appear as I see in the Lab doc, again with the Visual layer on? That is, you are trying to get the “luminosity” of the RGB doc to appear the same as the Lab doc as seen here?

http://digitaldog.net/files/Lab-RGB.jpg
Reply With Quote top
  #37  
Old 09-09-2010, 04:45 PM
andrewrodney's Avatar
andrewrodney andrewrodney is offline
Senior Member
 
Join Date: May 2010
Location: Santa Fe
Posts: 1,091
Re: L*a*b* question: why can't it be simulated in

Quote:
Originally Posted by Chain View Post
mistermonday:

That said, it was very easy in both LAB and RGB to match the brightness of the two colors using a gentle curves adjustment (brightening/dodging).
* In RGB the color did not visibly shift if blending was set to Luminosity.
On my end, it did a bit. If you set the sample points to Lab in the Info palette, the aStar and bStar do change a bit, I don’t know if that’s really an issue but yes, if your goal is to keep the two exactly the same while altering Lstar, Luminosity blend mode does cause the two channels to move. The aStar goes from 11 to 3, the bStar goes from -58 to -44.
Reply With Quote top
  #38  
Old 09-09-2010, 05:40 PM
mistermonday's Avatar
mistermonday mistermonday is offline
Moderator
Patron
 
Join Date: Dec 2005
Posts: 3,028
Re: L*a*b* question: why can't it be simulated in

Flashtones, thanks. For the moment I would be very thrilled if Doug could just get RP Live out of Beta. In the meantime I will see if put together a LAB retouched file for people to play with.
Regards, Murray
Reply With Quote top
  #39  
Old 09-09-2010, 06:47 PM
mistermonday's Avatar
mistermonday mistermonday is offline
Moderator
Patron
 
Join Date: Dec 2005
Posts: 3,028
Re: L*a*b* question: why can't it be simulated in

Andrew,
Quote:
Question: Can I assume that the goal is to have that top “Visualize” layer on, and see the upper right quadrant in the RGB doc appear as I see in the Lab doc, again with the Visual layer on? That is, you are trying to get the “luminosity” of the RGB doc to appear the same as the Lab doc as seen here?
No, sorry to making it difficult to get my point across. Put the LAB file aside for the moment and let me try to explain it differently with the RGB file.

-Imagine that the orange area is nice skin - its just right. Consider that the blue side is a freckle or a deep pore, too dark because it was inadequately illuminated, etc. The goal is to Dodge the top right corner and color correct it to match the adjacent nice skin.
-I add a Dodge / Brightening curve above the background layer, invert the mask so it's completely black and make a selection of the upper right corner.
- Turn on the visibility layer.
- I have dodged that upper right corner until visually the brightness of it appears to match the brightness of the orange side of the image. I think I did a pretty good job but for this example I make sure by making the visiblity layer active and changing my eyedropper samples to LAB to confirm that both eyedropper values are equal - in this case 58/58 but the number doesn't really matter, the goal was to match brightness.
- Turn off the visibility layer. (Color correct layer is still OFF).
- Looking at your image you see that while the freckle has been dodged and although its brightness matches the surrounding skin, its color / saturation does not match the skin exactly (in this extreme case it is bright blue. So we need to correct that.
- Above the Dodge curve, add a blank layer and set its blend to Color. Sample the right side orange (good skin) and now paint over the dodged blue corner. Behold the colors don't match because in RGB, when you add color you move the lightness.
- OK, so now according to Andrew and Chain, change the blend mode of the Dodge curve from Normal to Luminosity. You would expect the problem to be solved BUT it is not. It is close but if you look closely, the colors are not a perfect match. If you turn back on the visibility layer you will see that the two gray areas are not identical and if you check the color samplers you will see the brightness is different between the dodged corner and the right side. The difference is small if you measure with L and larger with RGB but if you have a reasonable monitor you can see a notable difference whether you view it in grayscale or color. This is the way RGB works. And while you tried to make RGB act like LAB by changing to luminosity blend - it is not the same.

Switch now to the LAB and walk through the same process. Notice that once you have dodged the upper right corner and to the point where its brightness exactly matches the that of the left side of the image, and you add a color layer and paint over the right corner, the color match is perfect because the lightness does not budge. In fact after you have matched the brightness you can paint with any color you want and the lightness won't budge. You don't need to go back and fiddle with the curve or dodge more or burn back. You don't need to add a Hue/Sat adj layer and fiddle with it to obtain the corrections you need, although you can just as you can in RGB.
I can show you this on real skin but I thought it would be easier for you to see it and try it with these dumb tiny files. Depending on the image and the amount of contrast and the intensity of the dodge curve the effect may be more or less difficult for you to see on real skin but the problem is the there.
Regards, Murray
Reply With Quote top
  #40  
Old 09-09-2010, 07:24 PM
andrewrodney's Avatar
andrewrodney andrewrodney is offline
Senior Member
 
Join Date: May 2010
Location: Santa Fe
Posts: 1,091
Re: L*a*b* question: why can't it be simulated in

Quote:
Originally Posted by mistermonday View Post
No, sorry to making it difficult to get my point across. Put the LAB file aside for the moment and let me try to explain it differently with the RGB file.
No, I get where you’re going with this (based on my post above about the a&b Star values changing). You want to affect just the tone without the color. It could be a legitimate issue I suppose. The good news (for me) is that tonal moves, using say the Exposure brush in Lightroom does so without any color change. Don’t have Lab values in that app but the percentages do update such that the ratio of color is maintained.
Reply With Quote top
Reply

  RetouchPRO > Technique > Photo Retouching


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Converting CMYK to RGB and back to CMYK. xxxmen Input/Output/Workflow 23 01-06-2011 11:56 AM
my 1st post..red cast on Lacie 324/CS4 RGB to CMYK nadaman Hardware 47 03-10-2010 02:31 PM
Adobe RGB (1998) profile problem * Sinisa Software 7 07-10-2009 11:08 PM
RGB Help PSE JohnTravers Salon 5 10-13-2008 07:28 PM
silly question Tinkerbella197 Photo Restoration 5 09-15-2008 11:46 AM


All times are GMT -6. The time now is 10:11 AM.


Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
SEO by vBSEO ©2011, Crawlability, Inc.
Copyright © 2016 Doug Nelson. All Rights Reserved