Some people have an inclination for color, some rather not, but even if you happen to be included in the latter you can improve with knowledge and practice. GIMP has all the typical tools needed to develop your skills on approaching color from every aspect. The more you get accustomed to these tools, the more you become effective on the technical level -- and you become more creative at manipulating color through personal techniques and styles.
In fact and trying to be precise, there is no such thing as "good method" or "bad method" to do something that someone might think of doing. So do not try to find the "best trick" to achieve this or that. There are possibly many ways to do this or that, and your best strategy will be to practice on all tools and techniques, trying to conquer the most tools and methods you can. Do not reject anything! The outcome of an action is almost never absolutely predictable, and every photograph has its own structure, so the same action in two different photos may well have a different outcome. Your technical skill together with your imagination is the combination that will be helping you on anything that you may want to accomplish.
However of course there are always recommended tools and methods for everything. What i can actually do for you is to demonstrate various tools, in a way to help you perceive different possibilities through different approaches of the same one subject matter: the digital image. This is what you have, this is what you will work on, this is what you will work for. And still more, you must keep in mind that apart from the technical side, there is the aesthetic and the artistic side of the thing you work on. I wish that later on little by little, you realize that the more effective you become technically, the more your artistic side opens up to new horizons as well.
A hint about the philosophy of digital color
We perceive as color something different than what a computer "perceives". A computer "knows" only numbers - nothing else, absolutely. When you see your photo on your computer, it is just a set of uniform primary material: a hell of numerical data representing other secondary data called pixels. Every pixel is again made of three numbers, every one of them between 0-255. In order for us humans to optically perceive the three primary data of the pixels, we consider them on the image level calling them channels: the Red channel, the Green channel, the Blue channel. This is all that there is to it, this is the digital image, nothing more, nothing less.
So while you work on your image performing various actions, the computer in the background constantly recalculates numbers. The more you understand how your actions affect the primary numerical data, the more skilled you become on digital image editing. No worry for numbers -a hell of numbers!- this is a task you leave upon the machine, you do not worry about them, you are only concerned about your actions and their outcome.
A few words about color management
A digital image may pass through various devices and media been used in your workflow. For example, an image taken with your photocamera and intended to be used in a printed material, will pass through the photocamera, your computer's monitor, the image editing application (be it the GIMP), the desktop publishing application in which the image will be used, the computer and the application where the output file will be opened during printing, the printer which will do the final print etc. These devices have their own characteristics. In order to address color yield compatibility problems, for us to be sure that "we see what we have", some device-independent standards have been set for color characteristics, described under the term color profile or working space.
If ever on opening an image file (that originates from a device or application) GIMP notifies you that the file has some embedded color profile prompting you to convert it to the inherent sRGB of the application, your safest bet will be to accept this conversion. This choise will let you work normally on the known three color channels R, G, B. For more information on this topic, you can read the relative GIMP's Help topic.
Three problems in histograms: clipping, spiking, gaps
These three phenomenons are generally considered as situations to be avoided in an histogram. The term clipping is used to describe situations where the black either/or white point is not properly set and pixels above/below those points are rejected/assigned on the same value. This means that there is a loss of tones since the tonal range has less values available, and we finally have an image with less tonal values. The term spiking is used to describe abrupt peaks in the histogram "where they should not be". On the two ends of the histogram it often indicates the presence of clipping, on the shadows showing as unwanted distortion on the image in the form of "pixelization" and on the highlights as blown out whitish areas with no detail. However normal spikes may be present in the histogram, in non-continuous images or photos that have large one-colored areas with no detail. Gaps usually appear after excessive contrast adjustments, either for the whole histogram or for certain tonal ranges, and, even worse, they may appear as by-effects on actions that are not primarily intended for increasing the contrast. Gaps always mean that some information has been lost. When in GIMP you expand a tonal range, on any type of information on any channel, it is inevitable that some of the intermediate values are going to lose their values.
These phenomenons are sometimes considered by experts as severe defects enough to judge an image as rejectable. Technically speaking in the strict sense, gaps in the histogram of a continuous tone image (ie. photograph) indicate jumps in values that are due to lack of intermediate transition tones. In real world situations, this is acceptable to a certain extend, depending on many factors, the most important of them being the actual image itself as seen on a moderately good and calibrated screen. For example, severe gaps in skin or flesh tones in portraits may cause noticable "banding" that can never be acceptable. On the other side, there might be a case of a photo with a technically awful histogram, which however may be an interesting and acceptable photo. Some people rely too much upon the histogram to judge the value of a photograph. Others claim that histograms are just useful tools in context, providing interesting technical information, and they judge an image on a "what you get is what you see" basis.
Reading the histogram at post-processing is an invaluable experience, which can make you a better photographer even from shooting, checking the exposure and the clipping at a glance on the histogram on your camera screen. As a general rule of thumb for shooting, the most important range to be properly captured is the highlights rather than the shadows, that is to say the right end of the histogram rather than the left, hence modern cameras often have a feature called highlight warning, which makes overexposed highlights in the image to blink while previewing immediately after the shot on the camera screen.
The frequency-step problem
Experimenting and practising with your own photos, you will realize that the last two tools must be used with caution, if you want to keep the natural colors of the photograph and stay away from digital alterations. With non-continuous tone images instead, these manipulations are easy: you can focus on a color and make color adjustments safely, since the absence of a color continuum lets you target a specific color area only. The frequency-step problem needs skill that you are going to gradually acquire, following along till Lesson 13.
Phew, what you have learnt!
In the last two lessons, you have learnt about the most basic and fundamental tools on color manipulation. I strongly recommend that you take your time at getting accustomed to using them. Offer yourself a couple of days just experimenting on your own photos. Play with them. Try all the tools and in every way. Shoot some test shots with varying lighting conditions, with varying exposures, and open them in GIMP and experiment. Play, play, play! Image editing can be a very creative and rewarding procedure for you as well! This is meant to be the best present you can make to yourself, if you want to be good at image editing.
To always have in mind: on a layer vs. on a selection
All the tools we have seen in the two last lessons, may act either
- on a layer, or
- on a selection -- if any.
It simply depends on a simple fact: is there a selection or not? If yes, a tool acts on the selection only. If no, the tool acts on the whole layer. This simply means that you have the important option of choosing, either the whole layer or a certain group of pixels on the layer on which to perform an action.
But still more on that, this is closely related to the concept of selection. What actually is a selection? This must be understood in order to fully get the power of these tools. A selection is actually not a certain group of pixels but all pixels at a certain degree each. So with these tools you have the ability to act selectively and at a controlled extend. The key is just the right selection -- and this is so important that it deserves a whole lesson later on. This puts extreme power to your hands. Simply put, you will soon be able to take any image and kick the hell out of it to your heart's desire.
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