The problem of accuracy
The popularity of books by Dan Margulis on color correction in the medium of amateur photographers is very high. And, it should be noted that the popularity of Margulis earned by right. And the new and old editions of his books contain a wealth of useful information both for professionals and for those who are just starting to get acquainted with the problem of correct color reproduction.
The trouble – in another. Unfortunately, many novice photographers somehow have the confidence that the advice Margulis will help them achieve the correct and accurate color on the image (no matter what was behind these epithets: the “right” and “accurate”).
If you buy an expensive album with reproductions of paintings and compare the reproductions with the originals, you’ll notice that, alas, accurate reproduction of all colors polygraphists not achieved. This issue is not simply about books for € 50. Alas, even in very expensive collectible editions colors are not reproduced perfectly. Why is this happening? Printers do not use color profiles? Do not comply with technology?Out of mind? Yes, no, of course. Simply, in most cases to accurately reproduce all colors in principle, impossible.
If the hand is not really expensive album of painting and to the Louvre or other galleries to reach too far, and tricky, the experiment can be simplified. In any search engine can, for example, to search for pictures on request: “Masterpieces, horsewoman. As a result, you get a lot of options for reproductions of classic paintings. And they will be noticeably different in tone. The author of this article could not resist and tried to follow his own advice (see Fig. 1).
Fig. 1. Art Masterpieces. Horsewoman. GTG. Variants of reproductions on the Internet.
Which of the options shown in Fig. 1, correct? A: Unfortunately, no. And do not think that the reason is only carelessness of those who prepared the images for publication on the Internet. The human factor is important. No doubt. But is it possible in principle to create a reference playback bryullovskoy rider for electronic publishing? Once again: alas!
In the first edition of his book, Margulis wrote: “Everyone needs calibration, all need to be able to control the color. However, obtaining excellent results (provided that calibration is not a substitute for the thought process) depends on the understanding that the world’s few absolutes and that the issue of human perception of color, say, hellishly difficult “(translated from the English author of the article).
All causes of errors in color reproduction can be divided into two broad classes: the technical limitations and characteristics of human color perception.
Technical difficulties
Technical problems on the way to an acceptable color reproduction occurs in abundance.
1. Not all colors in principle, can be printed. Some flow abroad gamut printer (gamut).These reproducible colors will be displayed closest possible color. This problem has no unique solution. And building color profiles also, alas, it does not solve perfectly.
2. Often when printing light colors are much more “float”. Repeatability for them less.The fact is that for light colors, even a tiny deviation from the required quantities of pigment (within the limits of technology) are noticeably on the eyes.
3. In the dark colors the human eye, by contrast, distinguishes between a small number of colors. Therefore, printers are often poured uniform black all the points for which the sum of CMYK-components, say, more than 95%. Some algorithms for inkjet and laser printers do the same thing.
4. An ideal uniform for Shading spot color printing press is impossible. As well as printing on the printer. Often this is due to the rasterization of the image. The picture consists of pixels, but also the pixel on the print is transmitted as a collection of smaller elements. Therefore, the result often depends on the technology of printing.Even with ideal profiling through channel printing, images, printed on an inkjet, sublimation and laser printers, will differ significantly from each other.
5. In the printing color can, to some extent depend on the angle at which the viewer looks at the image.
There are other technical problems … Generally speaking, the technique is not anything exactly. In all, there are tolerances, fit and error. Any engineering challenge – it is essentially a problem of creating something functional from non-ideal elements. A “uncompromising quality» ™ – a term marketing and sales.
Features of color perception by man
In addition to the technical difficulty of the task correctly color reproduction difficult and some physiological features of color perception. Take, for example, quoted by Margulis (see Fig. 2).
Fig. 2. The green bars on the right seem to be light green stripes on the left.
However, this is an illusion, as is easily seen by the computer pipette
from the program Photoshop (or any other similar).
Another telling example of the author of this article has somehow led to your site, when I wrote about photogenic. But the repetition of a huge disaster happens. Meet an old friend – the illusion of Adelson (see Fig. 3).
Fig. 3. The illusion of Adelson. Believe it or not – but the squares A and B are identical in color, brightness and saturation (of RGB-components are identical, as is easily seen with any graphics editor) © EH Adelson, 1995
One of the conclusions drawn from these examples is this: should not be one hundred percent rely on their perception of color. The use of expensive calibrated monitor – also not a guarantee of fair and accurate representation of colors. Computer pipette remains important and necessary tool.
Another important and common problem: the chromatic adaptation of the eye.Margulis both wrote about this phenomenon in the first edition of his book: “Although the calibrated monitor are urged to rely on him completely, without checking the numbers meaningless because of the awkward features of the human visual system, samopodstraivayuscheysya under outgoing from the source of light. In response to bright light, the eye reduces the sensitivity to them, allowing us to ignore the unwanted parts. And the longer we look at the image with a stranger colors, the more we cease to notice it, thanks to the phenomenon of humans chromatic adaptation.
This phenomenon can be easily observed when comparing the various reproductions of already mentioned “horsewoman” Briullov. Many of them are white pieces of paintings are not at all white. What is the matter? Inattention? Slovenliness?Unprofessional? No. It’s just that those who prepared the images for publication occurred chromatic adaptation of the eye. In the jargon in such cases say that the “eye zamylilsya. The solution again is to the recommendation to use computer pipette, and not to trust your instincts. In the worst case, you can seek the advice of another person, the perception of which had not yet zamylitsya chromatic adaptation.
The task of grading
But as soon as accurate and true color reproduction are unattainable, then why spend time on mastering techniques grading?
Margulis answers this question thus: “And now, criticized all stages of the printing process, we must say that it is actually not so bad. If we can not achieve on the printed page as a real image, or at least the image on film, so it is not available
anyone. The audience (consciously or subconsciously) understands this and makes the appropriate discount. Evaluating the quality of printed images, it compares with other print same images, but not with the original slides and, of course, not so that I could see in reality. ”
Thus, it is important to understand that an exact match with the reality of work not reasonable. The problem is posed differently.
The purpose of color correction – this is repeatability, predictability, and naturalness.On these three pillars and is based Professional work with color. On accuracy, whether we like it or not, we are not talking. However, this is a topic for separate discussion …
What? Where to go?
There is no doubt that the study and practical mastery of color correction techniques – a necessary and important. The main thing – to understand the objectives and capabilities. Alas, often amatours not think about it. As a result – disappointing and pointless wasted time.
The author does not undertake to say that he is well known that to study and where to start. If your intentions are serious, start with the study (and, no doubt, from thinking too!) Margulis books – really good option.
But many may be limited and less. Realizing that it is absolutely accurate color is not to reproduce, many are ready to restrict removal of extraneous color from the picture. Sometimes, in fact enough and a glance at the photo to see that image of “yellow”, “green”, etc. In this case, go back to the good old method of trial and error.
Incidentally, some people, printing photos in laboratories, mistakenly believe that having a profile for Photoshop for specific equipment allows us to hope for accurate color reproduction. Again, not too lazy to recall: the presence of a profile – a guarantee of predictability and repeatability, not accuracy. Moreover, many laboratories are embedded color profiles are ignored at the hardware level printers, which itself works with some errors. Conclusion: when it comes to achieving the desired result, recall the method of trial and error and have the presence of profiles.
Trying to make mistakes, you can navigate to the following scanty plate (see Figure 4).
Figure 4. Removing unwanted hue from images.
(Terms of the table, see the text of the article)
Fig. 4 left shows a list of unwanted tones, which must be eliminated in the image. In the table rows using the arrows symbolically shows that we must take to achieve this goal. At the same time in each row of unidirectional arrows must necessarily integrate the conjunction “and”. For example, to eliminate the undesirable green color (third row from top) should be: either at the same time reduce the components CYAN AND YELLOW, or to increase the component MAGENTA. Of course, if necessary, you can combine all three steps in one line.
Consider the application of this simple plaque in practice. Suppose we had printed out some images and found that the gray tones become undesirable orange color (the leftmost square in Fig. 5).
To avoid misunderstanding, it should once again emphasize specifically the fact that it is not about color correction of digital images on the computer, but the correction that seeks to compensate the errors of the press!
Fig. 5. Removing the orange tint
Beginners, of course, is not easy to see in “dirty” tint orange. But with a little practice to get the desired skill is easy. If the printed image can be digitized with reasonable accuracy, the problem becomes simpler: it is enough to increase color saturation, and a dirty shade of the extreme left of the square will be easily recognizable orange color (box in brackets). You can also make independently in Photoshop (or other similar program) file-plate “dirty” colors, and if necessary, consult with her. But it certainly is possible only if the monitor reproduces colors without large errors.
So how do you remove the unwanted orange hue with the above signs? Looking at the list of colors available, we do not find it orange. We’ll have to remember mnemonic reminder “every hunter wants to know where the white and blue. The orange color in the spectrum is located between the red and yellow. Compare the top two rows in Fig. 4. Arrows in the channel Magenta different direction. We assume that in the interim version with multi-directional offset each other. And in the other two channels is unidirectional arrows, ie, in the interim version of their action to save. So, to eliminate the orange hue in the leftmost square in Fig. 5 should increase the Cyan, Yellow, and reduce left unchanged Magenta.
The next question: where to implement these changes? Answers may be multiple. If you are printing on your home printer, you can try to make a correction in the driver installation. If you are working on neotkalibrovannom equipment, then you can make the correction directly in the file by using the Channel Mixer tool, or Color Balance (Photoshop). Paying for the lack of calibration will need to have two copies of the images: one – for print, another – for viewing on your monitor.
In computer simulation of the process the printed image author used tool Color Balance: -50 (cyan-red) and +50 (yellow-blue). The result is a square, as shown in Fig. 5 right. He, of course, not ideal gray: R = 175 G = 178 B = 177. But for the correction of a quick fix result is quite good.
In conclusion, it should once again draw the reader’s attention to the fact that the author did not call to abandon traditional professional tools and methods for color correction. Just like: in some cases, acceptable results can be obtained in a hurry, working with neotkalibrovannym channel.
Conclusion
According to the author questions the correct color reproduction and color correction – quite complex. Either they should be dealt with seriously and with full understanding, either initially should be limited to simple amateurish ways, similar to what has been described in the final section of this article. People “got stuck in the middle, would inevitably be disappointed.
However, the author, following the usual routine, do not dare to insist. If after reading this article, the reader has at least one issue or one less than the illusion, the author will consider his goal has been achieved.