Photoshop Lab Color: Ch. 1

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  • DavidTODavidTO Mod Emeritus Thousand Oaks, CARegistered Users, Retired Mod Posts: 19,160 Major grins
    edited September 12, 2005
    Humungus wrote:
    Didnt you blokes say to keep A & B the same ?


    Apparently each one needs to be symmetrical at this point, but they do not need to be the same. I guess in the future we're going to learn how to adjust them asymmetrically, but for now that's the deal. So the A highlights are moved an equal amount as the A shadows. Same for B, but B does not need to equal A.
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  • ruttrutt Cave canem! BostonRegistered Users Posts: 6,511 Major grins
    edited September 12, 2005
    In the book, Dan keeps A and B the same through most of Ch 1 and only at the very end of the most technical part does he give an example where he does not. At that point is arguing that this LAB adjustment can't be duplicated in any other colorspace.

    Anyway, I just wanted to restrict the recipe as much as possible at this point. More options tend to confuse people at first and the simpler the recipe the more likely it is that people will try it out.

    Chapter 2 is a pretty technical (and numerical) explanation of LAB. I'm going to write something about it this week. A few people have told me that it's intimidating. I don't think it has to be, so I'll try to help sort out what you really should know from stuff you can absorb over time.

    Chapter 3 is where we'll start changing the recipe. David volunteered to kick off that discussion by writing a summary of it once he gets his book and gets through the first two chapters.
    If not now, when?
  • TristanPTristanP Major grins Wilmington, DelawareRegistered Users Posts: 1,107 Major grins
    edited September 24, 2005
    Here's my try
    I don't know if this is the best image to try it on, but this technique has been intriguing me for awhile and I thought I'd try it tonight.

    Original

    path.jpg


    a+b curves

    a_curve.jpg
    b_curve.jpg


    After a+b curves

    path_ab_curves.jpg


    L curve

    l_curve.jpg


    After L curve

    path_l_curve.jpg


    Final after sharpening L only (100/1.0/10)

    path_final.jpg
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  • DavidTODavidTO Mod Emeritus Thousand Oaks, CARegistered Users, Retired Mod Posts: 19,160 Major grins
    edited September 25, 2005
    TristanP wrote:
    I don't know if this is the best image to try it on, but this technique has been intriguing me for awhile and I thought I'd try it tonight.

    Original

    path.jpg

    .........

    Final after sharpening L only (100/1.0/10)

    path_final.jpg

    How much processing did this image get before LAB? I'm curious, because the road is cool in the B value and warm in A. That makes for magenta and blue, which ends up looking kinda purpley.

    But your greens are very yellow. So if you were to add yellow for the road you'd throw the vegetation out.

    This image (IMO) is a more advanced problem. This requires work that won't be covered until Chap. 4 or later.

    Aside from those challenges, what you did (given the constraints of where we are with this) made sense and improved the image (while exagerating some problems already in the image).

    Try again with another image. It's good to work with an image that you know has an area that's neutral, or nearly so. Any neutral area will have A and B values of 0.
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  • SystemSystem Registered Users Posts: 8,195 moderator
    edited October 2, 2005
    rutt


    just to let you know I'm still here--

    trying to catch up on chapters 1-5 while working on chapter 6--

    will take chapter 9 or 10 but you might want to wait til you see how I do on 6--

    this is a pretty neat way to go thru a book, especially so technical, and get all the different viewpoints--

    interesting how you've asked for us to take these directions on faith and how some have difficulty doing just that--

    if any of these go to church I'm sure they're not the preacher's favorite--
    I never was but it was for other reasons--

    please don't get me wrong--nothing like some healthy skepticism and seeing all the different personalities coming thru--

    my guess is that when I get the opportunity to look at the galleries of your respondents that the photos will reflect their personalities--

    anyway, enjoying this and thanks to all who are participating--

    george
  • SystemSystem Registered Users Posts: 8,195 moderator
    edited October 2, 2005
    ps got called in to the hospital in the middle of the night (ultrasound tech) (always taking pictures) and did not get any sleep--


    just took some ambien which makes me somewhat looney and really shows when I'm on a forum--had to quit the high school sports forum because I was probably way too embarassing to my kids--

    so if I say something that offends, then f-f-forgive me, please--
  • ruttrutt Cave canem! BostonRegistered Users Posts: 6,511 Major grins
    edited October 2, 2005
    gefillmore wrote:
    ps got called in to the hospital in the middle of the night (ultrasound tech) (always taking pictures) and did not get any sleep--


    just took some ambien which makes me somewhat looney and really shows when I'm on a forum--had to quit the high school sports forum because I was probably way too embarassing to my kids--

    so if I say something that offends, then f-f-forgive me, please--


    Wow, I guess birds of a feather...
    If not now, when?
  • ruttrutt Cave canem! BostonRegistered Users Posts: 6,511 Major grins
    edited October 3, 2005
    You need to say more about what you did and what you were trying to accomplish here. Can you post the curves you used? Off hand, I'd say this image is also in need of a little TLC in the L channel.

    Really these posts belong in one of the chapter discussions if we only knew which one.
    If not now, when?
  • SystemSystem Registered Users Posts: 8,195 moderator
    edited October 3, 2005
    sorry--


    meant to put this in chapter 1 dialog--

    so engrossed in trying to get the photos posted that I lost track--

    I can get too 'focused'--

    use pc vs mac--for those who know, is it easier to post with mac??

    how are you posting your curves?

    does anyone know what a gates keyboard is?? (answer at bottom)




    administrator--if you need to or want to move my last few posts, no problem with me--mainly making sure I can get the photos up





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  • ruttrutt Cave canem! BostonRegistered Users Posts: 6,511 Major grins
    edited October 3, 2005
    gefillmore wrote:

    how are you posting your curves?

    I gave these instructions to Ginger and they seem to have worked for her:

    http://www.dgrin.com/showpost.php?p=162050&postcount=38
    If not now, when?
  • SystemSystem Registered Users Posts: 8,195 moderator
    edited October 3, 2005
    ok--is everybody posting to smugmug including graphics files and then on to the forum?


    I was using the manage attachments and it was very tedious--

    oh well, I will keep at it but right now I need to get back to chapter 4--

    thanks for the help--

    george
  • DavidTODavidTO Mod Emeritus Thousand Oaks, CARegistered Users, Retired Mod Posts: 19,160 Major grins
    edited October 3, 2005
    gefillmore wrote:
    trial run curves


    Whoa. Check out those curves!
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  • DavidTODavidTO Mod Emeritus Thousand Oaks, CARegistered Users, Retired Mod Posts: 19,160 Major grins
    edited October 3, 2005
    gefillmore wrote:
    ok--is everybody posting to smugmug including graphics files and then on to the forum?


    I was using the manage attachments and it was very tedious--

    oh well, I will keep at it but right now I need to get back to chapter 4--

    thanks for the help--

    george


    I use attachments if I'm only attaching one file. But for the LAB posts you need to attach (usually) a before and after and three curves. So in that case I would upload to smugmug first.

    In the future in order to show your LAB work show us what you started with, what you ended up with, and describe how you got there, showing the curves that you used to get there.

    We can't be much help without that info, and others can't learn from your experience without it.

    Keep on having fun. It's kind of addictive, ain't it?

    Oh, and also if you need specific help with the mechanics of posting, feel free to PM me.
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  • ruttrutt Cave canem! BostonRegistered Users Posts: 6,511 Major grins
    edited October 3, 2005
    DavidTO wrote:

    We can't be much help without that info, and others can't learn from your experience without it.

    I want to add something. It's very important when you retouch a photograph to have a goal in mind. If you don't, then at least when you are done you should be able to say what you acheived. Without at least one of these, it's very hard to access the technical success of your work. If you get in the habit of thinking in terms of goal directed photo retouching, you will learn more and do it more quickly than if you just fool around and try stuff until you think it "looks better".
    If not now, when?
  • SystemSystem Registered Users Posts: 8,195 moderator
    edited October 3, 2005
    rutt and david--


    thanks for the help and the advice--

    yes, it's addictive--


    george
  • photomomophotomomo Beginner grinner San FranciscoRegistered Users Posts: 4 Big grins
    edited October 10, 2005
    Is it just me??
    The flesh tones look fine but there is too much green with everything else???
  • StanStan Major grins 52.085 -0.095Registered Users Posts: 1,077 Major grins
    edited October 11, 2005
    I will try not to post too much while I catch up but if anyone can help with some early pointers...

    1 The sky turned the nastiest blue in the lake and desert images and did not resemble the colour in the book. I take it this gets addressed later in the book.(?) I noticed it also in Davidto's correction of Gus' plantation

    2 Sharpening the Lightness channel 200:1:10 made the rocks in the Yellowstone image far too sharp, has he done this for effect or have I missed something?

    3 Is it better to process a RAW image before converting it to photoshop or to open the image as shot and correct it all in Levels?

    Thanks for this fascinating course, I have only now found time to start it so am running very late...

    Stan
  • ThwackThwack Hobbyist Silly-cone ValleyRegistered Users Posts: 487 Major grins
    edited October 18, 2005
    I don't think the dry grass came out quite the right color but the clouds are a definite improvement after playing with the LAB curves.

    The grass looks a bit washed out in the posted version but it looked much better in Photoshop. Converting it to JPEG for posting seems to have washed it out a bit (I had the quality set to max).

    A & B were just pulled in 16% on each end. L was pulled in less on each end and a slightly non-linear curve was used so I could move the lighter and darker portions slightly differently.

    I forgot to take a screen shot of my L curve and I don't seem to be able to bring that curve back up afterwards (once that window is closed, there's no way to slightly tweak an existing curve???). headscratch.gif

    Oh yeah, I made a couple other edits while I was in there and forgot to save to a different file name before adjusting the LAB curves. For the "before" shot, I had to go back to the original which is lacking some cropping, reframing, and some other edits (no color adjustments though).

    "Before":
    40561352-M.jpg



    "After":
    40561171-M.jpg
  • pathfinderpathfinder Drive By Digital Shooter western IndianaSuper Moderators Posts: 14,658 moderator
    edited October 18, 2005
    There's more than just LAB curves here, as the image has been cropped and the telephone pole has been cloned out. But the overall tonality of the second image is much better to my eye. I like the color in the water much better too.
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  • DavidTODavidTO Mod Emeritus Thousand Oaks, CARegistered Users, Retired Mod Posts: 19,160 Major grins
    edited October 18, 2005
    Yep, looks better.

    What else you got? ;)
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  • ThwackThwack Hobbyist Silly-cone ValleyRegistered Users Posts: 487 Major grins
    edited October 19, 2005
    I have several pics from that river trip that I'm trying to clean up but I'm really struggling with the others. If I can make them presentable, I'll toss them up here (and I'll try to remember to save a copy before playing with the LAB curves so I don't have to post a 'before' picture that's lacking the reframing, cropping, etc). :)

    Thaanks for the comments folks.
  • Tom K.Tom K. I post, therefore I am. Connecticut, USARegistered Users Posts: 817 Major grins
    edited November 21, 2005
    I have been reading this thread with great interest. I have a problem that has been driving me up the wall for years.....and it's the fact that I am color blind. I can see colors but I have trouble differentiating between greens, reds, and browns when they are all mixed up in an image. So this LAB method could potentially help me with a "by the numbers" color correction routine........hopefully.

    I have been applying the methods in the thread (book is in the mail on it's way as I write this). I have come up with several dramatic improvements to images that have been sitting on my hard drive for a year or two now. The only thing I really have to figure out is the adjustments to the Lightness channel. Channels a and b I am OK with. Creating that final curve in Lightness has been tough.....mainly due to my color blindness.

    Anyhow....this thread is the reason I registered with this superb photograph forum. I fell upon it with a good old google search. Here's a split image I did using the basic chapter 1 method.

    52557462.LAB9.jpg
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  • pathfinderpathfinder Drive By Digital Shooter western IndianaSuper Moderators Posts: 14,658 moderator
    edited November 21, 2005
    Tom K. wrote:
    I have been reading this thread with great interest. I have a problem that has been driving me up the wall for years.....and it's the fact that I am color blind. I can see colors but I have trouble differentiating between greens, reds, and browns when they are all mixed up in an image. So this LAB method could potentially help me with a "by the numbers" color correction routine........hopefully.

    I have been applying the methods in the thread (book is in the mail on it's way as I write this). I have come up with several dramatic improvements to images that have been sitting on my hard drive for a year or two now. The only thing I really have to figure out is the adjustments to the Lightness channel. Channels a and b I am OK with. Creating that final curve in Lightness has been tough.....mainly due to my color blindness.

    Anyhow....this thread is the reason I registered with this superb photograph forum. I fell upon it with a good old google search. Here's a split image I did using the basic chapter 1 method.

    52557462.LAB9.jpg


    It warms up the image nicely. :):
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  • ruttrutt Cave canem! BostonRegistered Users Posts: 6,511 Major grins
    edited November 21, 2005
    Tom K. wrote:
    .....and it's the fact that I am color blind. I can see colors but I have trouble differentiating between greens, reds, and browns when they are all mixed up in an image. So this LAB method could potentially help me with a "by the numbers" color correction routine........hopefully.
    The second (more technical) half of Chapter 3 advances the theory that red/green color blindness really is magenta/green, i.e., A channel, color blindness. Dan has some interesting empirical evidence to back this up.
    Tom K. wrote:
    Creating that final curve in Lightness has been tough.....mainly due to my color blindness.

    When I took Dan's class two weeks ago, he made us correct a set of images with our monitors set to greyscale, so we had to rely entirely on the numbers for color info. The results actually looked pretty good in color. In some ways correcting like this is liberating because it removes the temptation to look at the image so hard and long that one can no longer see it. If the numbers are right, well if one can't see the colors, that's the best one c an do.

    Here is an approach for writing those pesky L curves which may help you. Turn off the visibility of the A and B layers (click on the eyeballs next to them in the layer palette.) Now you are looking at a B&W image. Adjust the L curve to make it look the best you can. And there is a by the numbers approach to that. Select light and dark points in the image, spots where you are willing to blow anything lighter or plug anything darker, respectively. Bring up the L curve and mouse over those points while left-clicking. You'll see a point on the curve representing the luminosity of the image at that point. Drag the endpoints of the curve close to thoee points (but not all the way there, you'll see why.) Now mouse over the areas of greatest interest in your shot (say a face in a portrait) and consider adding a point to the curve to make it steeper over those areas: perhaps just to the dark side and pulled up a bit or just to the light side and pulled down a bit.

    What some concrete examples? Why not post a couple you are having trouble with and I'll show you. Higher resolution is much better and easier, so please provide that if possible.
    Tom K. wrote:
    Anyhow....this thread is the reason I registered with this superb photograph forum. I fell upon it with a good old google search.

    On behalf of all the participants in the reading group, I'm flattered. Thanks.
    If not now, when?
  • Tom K.Tom K. I post, therefore I am. Connecticut, USARegistered Users Posts: 817 Major grins
    edited November 21, 2005
    rutt wrote:
    Here is an approach for writing those pesky L curves which may help you. Turn off the visibility of the A and B layers (click on the eyeballs next to them in the layer palette.) Now you are looking at a B&W image. Adjust the L curve to make it look the best you can. And there is a by the numbers approach to that. Select light and dark points in the image, spots where you are willing to blow anything lighter or plug anything darker, respectively. Bring up the L curve and mouse over those points while left-clicking. You'll see a point on the curve representing the luminosity of the image at that point. Drag the endpoints of the curve close to those points (but not all the way there, you'll see why.) Now mouse over the areas of greatest interest in your shot (say a face in a portrait) and consider adding a point to the curve to make it steeper over those areas: perhaps just to the dark side and pulled up a bit or just to the light side and pulled down a bit.

    What some concrete examples? Why not post a couple you are having trouble with and I'll show you. Higher resolution is much better and easier, so please provide that if possible.


    I am thankful for the quick response and extremely helpful info. The "L" curve method you described looks very promising. I have posted a very large original image along with my final rendition with a screen cap of the curve I used. I am quite sure the "L" curve could be improved upon as this is my first attempt at using your suggested method. Hopefully after practice (and with your assistance) I can get the hang of that "pesky" L curve technique. I use the USM settings of 200 > 1.0 > 10. Ten I resized down to 1200 x 800 with no further resharpening. As noted above I am color blind. My wife isn't and said that the final image looks good. That said.....she did not analyze the image closely.
    52573247.watch_hill_lg.jpg

    52573249.watch_hill_final.jpg

    52573251.watch_hill_LAB_curves.jpg

    I am so very thankful for the help.
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  • ruttrutt Cave canem! BostonRegistered Users Posts: 6,511 Major grins
    edited November 21, 2005
    Not exactly. Your L curve should look more like this:

    45421410-M.jpg

    What does this curve do? The horizontal (x) axis represents input L values and the vertical (y) axis represents output L values. The brightest spot I could find in the picture was in the clouds and it only measured about L=80. By moving the leftmost endpoint of the curve inward by about 15, I specified that anything with L=85 or more should become L=100, i.e., as bright as possible. The darkest area I could find in the original was in the roots of the grass about 1/3 in from the left. It measured about 10. By moving the right endpoint of the curve inward by about 10, I specified that this spot and anything darker than it should be as dark as possible (L=0). This L curve completely loses all contrast for anything lighter than that patch of cloud or darker than that place in the roots. But that's OK, because there is nothing else that light or that dark. That's how I picked those values in the first place. With this curve active, when I mouse over the picture with the left mouse button pushed, the point on the curve moves through the whole range of the steep part. The sky and clouds occupy the upper 1/3, the sand and tops of the grass occupy the midtones, and the roots live in the lower 1/3 of the curve. Now we are using the entire range of luminosity. Should look a lot better. Does it?

    45421531-L.jpg
    Full size
    If not now, when?
  • jfriendjfriend Scripting dude-volunteer San Francisco Bay Area, CaliforniaRegistered Users Posts: 8,097 Major grins
    edited November 21, 2005
    rutt wrote:
    Not exactly. Your L curve should look more like this:

    45421410-M.jpg

    What does this curve do? The horizontal (x) axis represents input L values and the vertical (y) axis represents output L values. The brightest spot I could find in the picture was in the clouds and it only measured about L=80. By moving the leftmost endpoint of the curve inward by about 15, I specified that anything with L=85 or more should become L=100, i.e., as bright as possible. The darkest area I could find in the original was in the roots of the grass about 1/3 in from the left. It measured about 10. By moving the right endpoint of the curve inward by about 10, I specified that this spot and anything darker than it should be as dark as possible (L=0). This L curve completely loses all contrast for anything lighter than that patch of cloud or darker than that place in the roots. But that's OK, because there is nothing else that light or that dark. That's how I picked those values in the first place. With this curve active, when I mouse over the picture with the left mouse button pushed, the point on the curve moves through the whole range of the steep part. The sky and clouds occupy the upper 1/3, the sand and tops of the grass occupy the midtones, and the roots live in the lower 1/3 of the curve. Now we are using the entire range of luminosity. Should look a lot better. Does it?


    Full size
    By way of making sure I what you're doing here, is this conceptually similar to "pushing in the ends" to the edges of the histogram in a levels adjustment layer?
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  • ruttrutt Cave canem! BostonRegistered Users Posts: 6,511 Major grins
    edited November 21, 2005
    jfriend wrote:
    By way of making sure I what you're doing here, is this conceptually similar to "pushing in the ends" to the edges of the histogram in a levels adjustment layer?

    Jeez, I don't know. I never use the levels histogram. Someone else will have to answer.
    If not now, when?
  • aporiaaporia Major grins Niagara Region (CAN/US)Registered Users Posts: 145 Major grins
    edited November 21, 2005
    jfriend wrote:
    By way of making sure I what you're doing here, is this conceptually similar to "pushing in the ends" to the edges of the histogram in a levels adjustment layer?
    The concept seems similar to me. Margulis recommends changing the defaults of the pure white and pure black points permanently to 97L, 0A, 0B (white) and 6L, 0A, 0B to improve the auto adjustment commands in every colorspace.

    Pushing or sliding in the ends in Levels or Curves also has a similar effect to using the eyedropper endpoint tools or adjusting the output numbers at the bottom of the histogram.

    Now, if I can only figure out how to color correct by the numbers, I'll be home free. :D
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  • DavidTODavidTO Mod Emeritus Thousand Oaks, CARegistered Users, Retired Mod Posts: 19,160 Major grins
    edited November 21, 2005
    jfriend wrote:
    By way of making sure I what you're doing here, is this conceptually similar to "pushing in the ends" to the edges of the histogram in a levels adjustment layer?


    If all you're moving is the ends, yes. Curves are much more powerful, but the ends would do the same thing as Levels.
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