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Ch 1, Professional Photoshop 5th Edtion
rutt
Registered Users Posts: 6,511 Major grins
[size=+1]Introduction[/size]
But I have learned how to think about color correction in a way that allows me to innovate and solve problems I have never encountered before. I have learned to love processing images and have come to be proud of my results (usually.) Mostly, I've learned to approach image correction as a craft with a huge engineering component that repays clear thinking about light, color, and vision.
You can take this as far as you like. In the first five chapters or so, the book covers simple techniques which will help nearly every image. Learn these and you'll be able to make quick corrections which will offer dramatic improvements.
Venture further and you'll be on your way to retouching as a competitive sport. This is not for everyone, but I've found it very rewarding.
[size=+1]Chapter 1.[/size]
Of swine and vision The book starts out with a before/after of one of Dan's photos from a recent trip to Italy. He doesn't say so, but people familiar with Dan's ideas will know that he has used curves to set light and dark point and and remove remove a slight yellow cast and then used USM to sharpen. It isn't the best that Dan knows how to do; it is the minimum he knows how to do. Anyone who looks at the two versions of this image will agree it looks more realistic after these corrections.
Since Dan starts with a before/after of one of his shots, I'll do the same and offer a before/after of one of mine. I've done more different things to this shot than Dan did to his, but everyone should agree that it looks more realistic after these corrections.
More realistic? What does that mean exactly? The camera is a mechanical device "sees" in a predictable and objective way. The colors and contrast it records, well aren't those what was actually there when the shot was exposed. Supposing that the exposure and focus were set properly, how can we possibly improve on that?
Our vision is very different from a photograph.
Following an image which Ginger posted posted (left) and my correction (right). I was very confident that nobody would prefer her version to mine. I carefully conformed to Dan's rules. I got much better contrast, particularly on his face. I corrected the cast to make the jeans blue and the fleshtones closer to plausible values.
Turns out I wasn't quite right. Ginger liked her yellow cast and at least one other person thought it was a more realistic take on artificial street light. Surprising. I can't see this, but that's what makes it interesting. I wonder what would happen if we took a poll?
But here is another comparison. Left is a naive B&W conversion of Ginger's image. I just did Image->Mode->Gray-Scale. The image right is the green channel with a pretty steep curve applied (and NO additional sharpening). Which is better?
The point here is that better contrast is nearly always preferable even when there is room to disagree about proper color.
Channel structure
The primaries in light are red, green, and blue. We can mix these different colored lights to get any color by altering their relative amounts. Monitors and slide projectors work this way. But when we make prints, the situation is different. Red ink reflects just red light and blocks the other two primary colors. Similarly for green and blue inks. So what if we want a yellow area in our image? How can we mix our primary colored inks to make yellow? Yellow light is composed of red and green light. Suppose we try to mix red and green ink? What happens? Well, actually, we get black. Why? Because red only reflects red and not green and visa versa. Put them together and nothing is reflected, ergo black.
So for printing, we need inks that only block one and reflect two primary colors. We call these colors cyan, magenta, and yellow. We say they are the opponent colors of red, green, and blue (respectively). Cyan blocks red and reflects the other two colors, &etc. Mixing cyan and magenta inks results in an ink that blocks red and green light, reflecting only blue. So in a world of perfect ink, we'd be in business with these three colored inks. Unfortunately, inks aren't a perfect as light, but that's a topic for a later chapter.
For now, we need to know that almost all printing processes add a fourth black ink (called K to differentiate from blue). So the CMYK color space was initially designed to model printers.
The quiz Don't panic. It's easy to be spooked by this. Don't let it get you. Nobody gets this right the first time. Not many people get it 100% right the tenth time. The big point here is that every image comes with 10 different B&W versions, or channels which might or might not come in handy for that particular image. In the case of the flower example, which is the best B&W? The answer depends on how dark you think those flowers should be. The cousin channels, red and cyan have by far the best detail in the flowers, but the flowers are also light. How to get this good detail into the dark red flowers, well that's a good challenge that we'll be working on during later channels.
One important take-away from the quiz is how similar the opponent color channels are. The red and cyan, the green and magenta, and the blue and yellow channels look nearly the same. Get your mind around this and why it's true and I think you will have learned something.
A second important take-away is the black channel. This version of the image which captures the edges so well will turn out to be a very useful tool if you keep it in mind.
There is a lot of detail which I haven't covered here. But there is nothing that we won't revisit in greater detail later.
Homework
Dan wants us to know he is going to teach us to make photographs look very much better than the originals. But he is also going start us on the road to thinking about how to improve our images as much as possible, to make them look as good as or better than he, Dan Margulis, could make them look. No, it won't be enough to read this book once and read the L.A.B. book once and practice constantly and go to Dan's classes. That hasn't been enough to teach me to make corrections which are competitive with Dan's, at least not more often than once in a long while. Mostly when we both correct an image, his cuts mine.Unattributed Beta Reader wrote:Here is a meta thought. People who are reading your books for the first time may take a while to understand what you are about. I have to explain all the time that you are not offering recipes the way other Photoshop authors do, but rather teaching people to think about color correction. In the process, you consider case studies and offer techniques. But the successful reader will come away with much more than just a catalog of techniques.
But I have learned how to think about color correction in a way that allows me to innovate and solve problems I have never encountered before. I have learned to love processing images and have come to be proud of my results (usually.) Mostly, I've learned to approach image correction as a craft with a huge engineering component that repays clear thinking about light, color, and vision.
You can take this as far as you like. In the first five chapters or so, the book covers simple techniques which will help nearly every image. Learn these and you'll be able to make quick corrections which will offer dramatic improvements.
Venture further and you'll be on your way to retouching as a competitive sport. This is not for everyone, but I've found it very rewarding.
[size=+1]Chapter 1.[/size]
[imgr]http://colortheory.smugmug.com/photos/115777776-L.jpg[/imgr]Dan Margulis wrote:If we alter the photograph to make it look like what we would have seen if we had been in the position of the camera, it will look better. That's the whole case for aggressive color correction in a nutshell
![http://colortheory.smugmug.com/photos/115777776-L.jpg[/imgr]](http://colortheory.smugmug.com/photos/115777776-L.jpg[/imgr]){kind=link}
Of swine and vision The book starts out with a before/after of one of Dan's photos from a recent trip to Italy. He doesn't say so, but people familiar with Dan's ideas will know that he has used curves to set light and dark point and and remove remove a slight yellow cast and then used USM to sharpen. It isn't the best that Dan knows how to do; it is the minimum he knows how to do. Anyone who looks at the two versions of this image will agree it looks more realistic after these corrections.
Since Dan starts with a before/after of one of his shots, I'll do the same and offer a before/after of one of mine. I've done more different things to this shot than Dan did to his, but everyone should agree that it looks more realistic after these corrections.
More realistic? What does that mean exactly? The camera is a mechanical device "sees" in a predictable and objective way. The colors and contrast it records, well aren't those what was actually there when the shot was exposed. Supposing that the exposure and focus were set properly, how can we possibly improve on that?
Our vision is very different from a photograph.
- We instantly and unconsciously allocate contrast to see more detail in the objects that are of more interest to us. This is called simultaneous contrast. The camera can focus. It can expose. It cannot easily allocate contrast to suit interest.
- Our vision is self-calibrating. This is called chromatic adaption. We see ambient light as neutral even when it is quite distinctly colored. Look at a gray card under tungsten, fluorescent, halogen, daylight, strobe, and stage lighting. It will always look gray, not yellow, green, blue, whatever. Anyone who has ever struggled with color balance knows that's not what the camera sees.
- We are very good at distinguishing the edges of objects even in low light and even when they are of like color to their backgrounds. How many times have you been disappointed by a shot where the subject didn't stand out well against the background or other elements of the shot.
- We see in almost impossibly high dynamic range compared to any existing camera (or output device for that matter.) People back-lit by bright noonday sun? No problem, we can see enough facial detail to know if they are happy to see us or not. Reflections on skin (as from a flash)? We just don't see them. Even the best camera, on the other hand, is a poor instrument by comparison. Just try taking a picture into or out of a window in daylight.
- Casts When photos show the impact of ambient light on known colors, this is called a cast. Cameras also see mixed casts from mixed lighting sources and reflections which we might not see. Dan says that green casts always look stupid, but that some warm casts are desirable.
- Contrast Generally we like more contrast through the area of interest in a photo. It is possible to disagree about what is the area of interest.
- Sharpening Just how much sharpening looks good where people have quite a bit of difference. Dan is sort of on one end of the spectrum -- he like a lot of sharpening and doesn't care if it's sometimes visible. But there is nobody who prefers no sharpening so long as the sharpening is effective.
Following an image which Ginger posted posted (left) and my correction (right). I was very confident that nobody would prefer her version to mine. I carefully conformed to Dan's rules. I got much better contrast, particularly on his face. I corrected the cast to make the jeans blue and the fleshtones closer to plausible values.
Turns out I wasn't quite right. Ginger liked her yellow cast and at least one other person thought it was a more realistic take on artificial street light. Surprising. I can't see this, but that's what makes it interesting. I wonder what would happen if we took a poll?
But here is another comparison. Left is a naive B&W conversion of Ginger's image. I just did Image->Mode->Gray-Scale. The image right is the green channel with a pretty steep curve applied (and NO additional sharpening). Which is better?
The point here is that better contrast is nearly always preferable even when there is room to disagree about proper color.
Channel structure
The primaries in light are red, green, and blue. We can mix these different colored lights to get any color by altering their relative amounts. Monitors and slide projectors work this way. But when we make prints, the situation is different. Red ink reflects just red light and blocks the other two primary colors. Similarly for green and blue inks. So what if we want a yellow area in our image? How can we mix our primary colored inks to make yellow? Yellow light is composed of red and green light. Suppose we try to mix red and green ink? What happens? Well, actually, we get black. Why? Because red only reflects red and not green and visa versa. Put them together and nothing is reflected, ergo black.
So for printing, we need inks that only block one and reflect two primary colors. We call these colors cyan, magenta, and yellow. We say they are the opponent colors of red, green, and blue (respectively). Cyan blocks red and reflects the other two colors, &etc. Mixing cyan and magenta inks results in an ink that blocks red and green light, reflecting only blue. So in a world of perfect ink, we'd be in business with these three colored inks. Unfortunately, inks aren't a perfect as light, but that's a topic for a later chapter.
For now, we need to know that almost all printing processes add a fourth black ink (called K to differentiate from blue). So the CMYK color space was initially designed to model printers.
The quiz Don't panic. It's easy to be spooked by this. Don't let it get you. Nobody gets this right the first time. Not many people get it 100% right the tenth time. The big point here is that every image comes with 10 different B&W versions, or channels which might or might not come in handy for that particular image. In the case of the flower example, which is the best B&W? The answer depends on how dark you think those flowers should be. The cousin channels, red and cyan have by far the best detail in the flowers, but the flowers are also light. How to get this good detail into the dark red flowers, well that's a good challenge that we'll be working on during later channels.
One important take-away from the quiz is how similar the opponent color channels are. The red and cyan, the green and magenta, and the blue and yellow channels look nearly the same. Get your mind around this and why it's true and I think you will have learned something.
A second important take-away is the black channel. This version of the image which captures the edges so well will turn out to be a very useful tool if you keep it in mind.
There is a lot of detail which I haven't covered here. But there is nothing that we won't revisit in greater detail later.
Homework
- Examine the channels in RGB and CMYK of some of your images. People, skies, flowers, buildings are all good examples.
- Try some of Dan's experiments. Copy the contents of one channel into another. What happens? Why? Post examples that baffle you.
- Dig through recent dgrin posts and see what you think about the color and contrast. Are there any colors that look really wrong to you? What about contrast? Think about why
If not now, when?
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Comments
Duffy
Thanks!
The trouble is that the term "simultaneous contrast" deals not only with tonal contrast, but also with color contrast. We are better at cameras at focusing on a part of a scene and distinguishing tonal differences in that part. We are also much better at distinguishing subtle shades of color in a scene where a camera does not draw out the same color distinctions. (Bringing out the second kind of contrast is where LAB excels.)
BTW, there are other things that people are good at doing that cameras cannot do. For example, suppose there is a landscape with some power lines or telephone wires in the foreground. On the scene, people are really good at ignoring this sort of clutter and focusing on a subject. I believe that is one of the reasons why so many snapshots stink. Having ignored the clutter, the person looks through the viewfinder and continues to ignore the clutter and focus only on the subject. Then they see the picture in print or on screen and wonder where those ugly power lines came from.
Part of being a photographer is training yourself to see what the camera will see. Also, while we tend to interpret grey as grey regardless of the ambient light, it is possible to make the ambient light so extreme that the phenomenon stops. (As an extreme example put on a black light and start looking at neutral objects under it.) And, if you want, you can also train yourself to start seeing casts from certain kinds of light. You can see the green in flourescent lighting, the orange in tungsten, and its easy to see the warm colors of either candlelight or firelight. In some ways, I think this sort of thing is like the difference between perfect pitch and relative pitch.
Duffy
There is a subtle but important point which I meant to cover. The box on page 9 titled When Do the Eye Adjust discusses what conditions cause our vision to perform chromatic adjustment and simultaneous contrast. Essentially, immersion in a visual environment causes us to adjust for it. The photo shows a late afternoon street scene during the first snow storm of the year. The camera accurately recorded the relative yellow warmth of the artificial light inside and cool natural light outdoors. This is one situation where chromatic adaption seems (at least to me) to snap on and off. I can see that yellow if I look for it and focus on the street scene. I can see the interior in proper color balance if I look at it. What I can't make myself see is proper interior color balance AND a cool cast on the faces outdoors. Probably this is because
Implications for color management and calibration: How many of you have had the experience of editing a photo until it looks good on your monitor and then being disappointed by the print. This happens even in color managed environment and to people with elaborate calibration systems. Ask Baldy who has to look at complaints from people who don't like their smugmug prints. See this post, or this one. I'm sure Andy has lots of stories like this as well.
So what's going on here? Color management is supposed to make the monitor image look exactly the same as the printed version. Gamuts are matched, and often that's not the issue anyway.
Chromatic adaption and simultaneous contrast provide the explanation. Looking at the monitor, especially in the process of concentrating on an image correction is immersive in a way that looking at a print is just not. The monitor dominates our visual field and provides its own light. The print is seen in ambient light, usually smaller than a monitor.
I've found that I'm often fooled by the look of an image on the monitor. But the numbers are, well the numbers. So I've come to rely more on measuring colors to determine whether there is a cast or not and to figure out if my image is really using a full range of contrast in the areas of greatest interest.
When the shot only includes the interior, I think the yellow cast should go. If a person focuses his attention on the interior, then he usually will be able to turn off the yellow cast. But in either 2 or 3, I don't think there is a right answer. It would depend both on the shot itself, and the spin you want to give it.
One other thing on that shot: don't the jeans on the outside look bluer than usual? and even the snow falling seems (at least to me) to have a tinge of blue. I don't know if its really there; its just how it looks to me at first glance. (BTW, this picture is a really nice analogue to the Hopper Night Cafe you posted elsewhere).
Duffy
As to the snow, I do think that snow in shade is a little blue. But that's a long and differerent story.
One think I often see in mammal shots is a blue cast (fur) why? And why does it seem normal, or correct?
There is a long story behind this question. Thusie, why not post some of the old blue squirrel shots and the before/afters. Also you told me that someone recently corrected some of your squirrels to be blue. Can you provide a link to that thread?
I've had my own experiences getting the Cyan out of pictures of my Labrador Retriever. Now we know that labs aren't cyan, don't we? Dan Margulis once scolded me for leaving a cyan cast in a dog's nose (yes happened to be a lab).
Here is a rule of thumb. Don't be too sure it is right until you print it and it still looks right. As I said above, the monitor will fool you, no matter how well calibrated and color managed.
http://www.dgrin.com/showthread.php?t=48861
I would assume the before and after blue sq shots would go into the gallery set aside for PP5E? Or do you want them here?
Gray sq fur is banded, black, brown and white and in shadow, where they seem to be most times, the brown becomes invisable (seems to) leaving mostly black and white. Since black and navy blue are quite close, with the bit of white+ shade= blue cast?
Rabbit and groundhog fur, also banded, will do the same. So I'm thinking it is those colors and light or lack there of and how that light reflects???
What's the point? If you take a pure white dog, like one of my Samoyeds, and put it outside under those conditions, then the side of the dog that is lit from the west will be reddish yellow, and the side that is toward the east will be bluish. How much a person can see this in the live surrounding will depend on how strong the effect is, where the person is in relation to the subject, and how sensitive the person is to color. If the dog is backlit, the reddish orange fringing around the fur will be obvious. If the light is side light (person standing North or South of the dog), then the white dog might appear bluish on one side and red on the other. More likely, the reddish side will appear warm, and the eye will adjust the blue to be neutral.
Shadows areas are always naturally more bluish than lit areas. There are a variety of ways to adjust these. The idea that the white fur is never blue is fine under normal lighting conditions, and probably fine even for a very large range of lighting conditions. But there are times when fur appears bluish, at least to some people's eyes.
The squirrel in the link above should obviously have white fur. But if you had a shot of a polar bear on a snow field in mid-morning, surrounded by bluish ice, and if half the bear was in shadow, then I think there is a range of choices on how to render the shadow fur, and a slight blue in that fur is not something I would reject just because there is a rule.
BTW, I take lots of pictures of dogs. I run accross this blue on shadow side, yellow on lit side almost every time I take pictures, and I'm still trying to come up with the best ways of dealing with it. Making the dogs appear all white has always been unsatisfactory, but that may just be a reflection on my technique. Now, I tend to warm up the entire picture, or sometimes warm up the shadow side to neutral, but lessen the effect on the lit side with the "Blend if" sliders. And I've taken many pictures of black labs and thrown almost all of them away. That slick black fur is really tough to get decently.
Duffy
At issue isn't the white fur, it is the top fur. Plus if you add a color cast either by choice or accident and don't make it specific you gobally change the colors in the whole shot. Would that be the correct thing to do or not?
So getting back to the sq shot, when was it taken? Is there any reason for the fur to have a blue cast, not belly fur but top fur? Better yet, after almost a month of driving Rutt nuts, I trained my eye to really look at the sqs in all types of lighting and their fur is never blue.
The shot below is in extremes of early sun and shadow, there are only two tiny spots, none on the top fur, that have a slight blue cast, and I just found them, slight but there. Most would never notice. I'm sure black labs are tough!!!
http://thusie.smugmug.com/gallery/2154157/2/116478551/Large
It's usually pretty easy to kill the blue with either Photo Filter or by using a LAB curve adjustment in B. If you do either move on a new layer, you can then typically do a "Blend if" that applies the move only where the original layer has a positive blue value. (There are even ways to do this without hitting the sky). Then it is a trivial matter to move back and forth between the two corrections in the History palette to decide which works better.
In short, I don't think there is a right answer to this question, even though there are probably very many wrong answers.
Duffy
1. to reproduce a photograph as accurately as possible,
2. to reproduce what a viewer who was in the position of the camera would have seen.
Throughout this book Margulis seems to support the second option, but I think he even goes beyond that, and will modify a photograph just because it will look better; even when a viewer in the position of the camera would’ve seen it. An example of this is the women with the purple shirt and the canal with the pink cast. His decision to modify or not modify was not based on whether a human would’ve seen it, but his subjective view on what looked better.
I found this chapter pretty informative, especially the parts on the human visual system, and what differentiates it from the lens of a camera. The only part I didn’t fully understand was the purpose of images 1.8C and 1.8D, where he mixes the other blank channels in at 50%.
Trent.
Brisbane Property Photos
Hey I really liked 'blue' sqs
Thusie, I wasn't to replying to the blue cast topic. I was replying to the first post as a general comment on the chapter. Thats why you probably didn't understand my post.
Trent
Brisbane Property Photos
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