User:MjolnirPants/Colorizing

Colorizing a grayscale image is actually a lot more complicated than just adding the right drops of color. Different objects handle light different ways. I'll start by going over how different kinds of materials deal with color, then we'll get into shadows.

Before you begin
You will need a few things before beginning.
 * A photo editing program Adobe Photoshop is the industry standard, but GIMP is a free alternative with pretty much the same functionality. I personally use both, and have a slight preference for GIMP for colorizing.
 * A properly calibrated monitor This can't be emphasized enough. See here for a useful guide to calibrating the monitor of a Windows 7 or later or Mac computer. If you want to be really exact, you can pick up some Pantone swatches at most paint stores, then download images of those same pantone shades on your computer. Using the program you intend to work in the most, compare the real swatches to the digital ones and adjust the monitor until you get very close matches across the spectrum of colors (blues, greens, yellows, oranges, reds and purples).

There are also a few things I highly recommend.
 * A graphics tablet Painting with a mouse is like painting with a brick. It can be done, and in fact is not quite as bad for editing existing photographs (including by colorizing them) as it is for creating new artwork, but the difference between having the tablet and not is night and day.
 * A selection of web browsers and devices You're going to want to check the image in a number of web browsers and on a number of different devices, to make sure it looks good under multiple conditions.
 * Lots of reference materials You can do it without references, as the ultimate judge of quality is your own eye, but I wouldn't recommend it.

Materials
Different materials must be colorized in different ways. The main aesthetic issue with colorized photographs is that the colorist treats all the materials identically. By colorizing the different materials in the correct ways, you can produce much more realistic results.

Metals
Metals show reflections, meaning that the colors on a piece of metal will be influenced by the colors of the objects it is reflecting. This category includes hard plastics and polished stone. Metals also have their own color. For perfectly reflective chrome surfaces (such as a mirror), this isn't a concern, but for other materials like gold, aluminum and titanium, you will need to account for this. Do this by coloring the entire metal surface with the base color. Then, at a lower opacity, color in the colors of the reflected object. The shadows (as discussed below) on metals are different than on other objects: They are always the same shade as the metal. Do not confuse the shadows on the metals with the shadows on the objects that are reflected in the metals. Below are some RGB values for metal base colors:

For hard plastics and polished stone and other such materials, you must use your best judgement as to what the base color is. It can be anything, and it can even have multiple shades in it. As a rule of thumb, the more detail there is in the material itself, the less it will reflect other objects.

Glass & Water
Glass and water work much the same way as metals, except they are transparent, meaning you can see objects behind them. Most of the time, there will not be enough of a base color to matter with glass and water, so it will take on the base color of whatever is behind them. However, as glass and water get thicker, they take on shades of color. Most people think that water is blue, which isn't exactly true. There is a very slight blueish shade to water, but the main reason water appears blue is because it is reflecting the sky. Whenever you have a scene with water and glass, you must ask yourself how thick it is. If it is not very thick (less than a foot or so), you will not be giving it any base color. Instead, you will be filling it with the base color of whatever is behind it, then adding to that with the colors of whatever it is reflecting. When in doubt, use a sky blue. Colored glass and water will, of course, have a base color. This can be any color imaginable, so I'm not going to provide examples.

Cloth Wood Stone & Leather
Cloth, wood and leather (and other similar materials) are some of the easiest to color. Basically, full coverage with the base color will do. Be careful, because many such objects can have multiple base colors. Leather especially will tend to have two or three different base colors, which are all very close to each other. Usually no more than plus or minus 10 to each channel (RGB).

Skin
Skin is the most difficult material to color. There will be at least 2-6 different colors used. As a general rule, you will always start with a very pale orange for non-Sub-Saharan Africans (even for such people with very dark skin) as the base color. Sub-Saharan African people will tend to start with a medium brown color. This is a mix of the color of the actual skin tissue and the color of the thin layer of fat behind it. Where the skin is perpendicular to a line drawn from the camera to the skin, it will tend to be almost exclusively this color, except for very tanned people. This is the "base" color of the skin, and you can use the same base color on many people of different skin tones, as you will be adjusting it later on.

Once you have a base color down, the next thing to consider is mottling. Skin is hardly ever a smooth, even tone. Even people with very smooth skin colors will have some slight mottling. I've found that shifting the base color tone the yellow, then towards the red, provides two additional tones that can be used to create a nice contrast. Remember to keep this adjustment very slight, unless you want it to be clearly noticed. These colors should never cover all of the visible skin; they should be stippled or scribbled in, to make a semi-random distribution. You will account for less random elements later on, with the skin curvature and blush colors.

Where the skin curves away from the camera, it will take on a deeper orange shade. This is a result of the skin tissue coming to dominate over the fat layer beneath it. This effect is very subtle, and usually cannot be consciously noticed, but it will make a difference in the finished image. When the area of skin to be colored is very small, such as with low resolution photographs, this color can be omitted.

The third color is a pinkish tone. This is the color of the skin where the capillaries are very close to the surface. Noses, knuckles, cheeks, elbows, eyelids and the areas of the body which are generally very sensitive, such as armpits and groins will all have a slight pinkish cast to them. Lips and nipples will quite often have a much deeper pink color, as well as being a shade or two darker.

The last color is optional for many Caucasian people, and it's the color of the melanin in the skin. This color must be judged by eye, and is usually applied as an overlay on the base color (after the mottling colors). There are three basic categories of this color; Peach, Olive and Brown. Peach is a slightly darker and less saturated version of the base color. Olive is low-saturation olive tone, with a bit more emphasis on the yellow than one would usually consider 'olive'. Brown is a dark, highly saturated version of the base color. Below is a table containing some of these colors. Note that these colors represent typical shades. People with dusky or tan skin might use more yellow shades, while people with paler skin might use more pinkish shades. Most differences in lightness of skin tone can be accounted for by using more or less of the curvature color. For people with very dark skin, you will need to add additional adjustments after this is done. For people with very pale skin, you will not need to add any peach, olive or brown overlay.

Shadows and Lights
In the real world, there are two kinds of light: Directional light and ambient light. The directional light is what we usually think of as light. The sun, lightbulbs, street lights, television screens and the reflections of these things are all kinds of directional light. The ambient light consists of the light which has bounced off of objects in the scene, and then goes on to strike other object. The ambient light is what determines the color of your shadows. Outdoors, the largest source of ambient light is the sky, which explains why shadows tend to be blue. Indoors, the ambient light will get colored by all the objects in the room, as well as the directional light source. These shadows are often greenish, but can be brown, purple or blue.

Shadows and lights can be tricky if you're not familiar with the basic principles. There are two:
 * First is that light colors. This means that the areas not in light (the shadows) will have a slightly different base color than areas which are in the light. Sunlight is slightly yellow (it's actually quite yellow, but our eyes work to hide this from us), halogen lights are even more yellow for the most part (this is the most common sort of interior lighting in homes); florescent lights are a very bright, low saturation green color (think of an office building, such as Neo's workplace in The Matrix); sunsets tend to be a richer, slightly redder shade of sunlight; and sunrises tend to be a richer, slightly bluer shade of sunlight. When picking the base color for an object, remember that these light colors should modify the base color, not replace it. That means to take what you think the color of the object would be under perfectly white light, and move it a little bit towards the light color. Also bear in mind what I said about our eyes correcting for the color of light sources: When you look at a room in your home at night, it seems like your lights are white, but when you snap a photo with your camera, you get a strong orange tint. That's not an artifact of digital cameras, that is the actual color of the room. When you are colorizing an image, bear in mind that you will need to find a middle ground between what you think that scene will look like, and what it would actually appear like if the photograph were shot in color.
 * Second is that shadows are always colored by the ambient light. I know I already mentioned this, but it bears repeating. In most outdoor scenes, this will mean the sky, making shadows varying shades of blue. Indoors, this can be green or brown, depending on the light source and the dominant colors in the scene. If the image is predominantly warm colors, the shadows will be warm. If the image is predominantly cool colors, the shadows will be cool. Don't presume that a lot of warm colors require cool shadows just for the sake of contrast. This sounds good on paper, but once you start colorizing you'll see that it just doesn't look natural.

Below are some common examples of shadow and light colors:

Technique
There are a couple of things to remember once you sit down to apply the colors you've decided upon.
 * First is that real-life is never as saturated as you think it is. Looking at the shade in the color picker, you will settle on something that looks perfect. But once you apply it, you will find that it gives the material a bright, cartoonish quality. There are a couple of ways around this, but the best results come from using a mixture of all of them.
 * Second is that the color of an object, and the color it appears to be are not often the same thing. For instance, one might picture brown leather as being a rich brown shade . In fact, brown leather is more red, less saturated and brighter.
 * Here are the two colors side by side for comparison:


 * Third and finally: Your eyes are your friends. An artistic eye is absolutely required for this, it cannot be automated. That means that you must be able to look at the image as a whole and adjust individual elements until they work together. You should always use a program like Gimp or Photoshop, which lets your work on layers which can be modified or erased independently of the rest of your work.

Preparation
Preparing your image for coloring is the first thing you must do. In this case, I am starting with the following image:
 * Tools: Healing Brush or Clone brush, 100% Opacity, soft round

Once all of the major artifacts are removed, you can proceed to adding color.

Skin

 * Tools: Brush, 100% opacity, soft round
 * Airbrush, 100% opacity, soft round, 80% rate, 10% flow

I recommend colorizing the skin first. It requires the most effort and time, and if you save it for later, you may find yourself rushing to finish. Start by creating a new layer, and using a brush (not airbrush), trace around the outline of all the regions of skin showing with a very pale orange color. If the skin appears too orange, you can lower the saturation or value of the color you are using until it looks right. I do not recommend over-saturating the face, although you may over-saturate other objects later on purpose.

Notice how the blush and shadows colors interact. In some regions, the blush color stands alone (the bottom edge of the eyes, for instance), in others, it seems to be a lighter sort of shadow (such as on the cheeks). This is one of the major differences between good and bad coloration: The use of multiple shades. If you closely examine the artwork of talented painters, you will see that they almost always use 2-4 different colors to depict skin.

Hat

 * Tools: Brush, 100% opacity, soft round
 * Airbrush, 100% opacity, soft round, 80% rate, 10% flow

Colorizing the hat is similar to colorizing the skin, but much simpler. In effect, there are only two colors involved in this step; the base color and the shadow color. With larger images, your base color may be more involved, showing mottling and color textures, but in this case, the image is too small for that to be necessary. So we start by creating a new layer, with its mode set to color. Then, we paint in the base color just like we did on the skin. Note how I used the hat color to color in the hair and eyebrows. Normally, I would not recommend this, but with an image this small, subtle variations in color can get lost in the final product, so there's no need to include them.

The Rest
At this point, I'm going to stop documenting the steps I took.. The shirt, the sash and the feathers in the hat were all colored using the same technique as the hat. The only exception was the shirt, which -being white- only required a shadow layer. As a general rule, there are only the four kinds of materials mentioned above. If it's not metal, transparent or skin, then it's going to be colored with only 2-6 shades, tending towards the lower end of that estimate. In large, detailed images, you may use a different base color for the lit regions of an object, as well as adding mottling or color texture to it, but medium and small sized images will usually only need 2 colors per object, the base and the shadow. The key thing to remember is that you will hardly ever stick to just one color. Following are a few more general points about technique.
 * The shadows on metals and liquids or glasses tend not to be the usual shadow color used in the rest of the image. Instead, get a color that is blended between the base color of the object and the shadow color. About 2/3 base object to 1/3 shadow color. This is due to the way that the ambient light interacts with the object: If an object reflects the red parts of the directional light, it will also reflect the red parts of the ambient light.
 * In the case of multiple light sources, making each one a different color will add to the realism. Even if they are all the same kind of light, such as halogen lights, each one will have a slightly different shade. This doesn't need to be very obvious, but making it just different enough to notice when the light spots on an object from each source are right next to each other will do wonders.
 * When working with the layers, color is not the only mode to use. There is also screen, overlay and multiply. Multiply will darken things, screen will lighten things, and overlay will mimic the effects of placing a film over it. Experiment with different modes to find the right combination that works for you. (As a general rule of thumb, richer, more saturated objects will tend to use multiply, bright highlights will tend to use screen, and glasses and metals will tend to use overlay).
 * Use reference images! This is one of the most overlooked details in art in general. Many people will criticize artists who use reference images, but those people don't know what they're talking about. Anything that improves your art is a part of your technique.
 * The point I mentioned earlier about real life being less saturated than you think is important. The final step whenever I colorize something is to create a new layer from the combination of all the layers I've created so far. Then I turn off the color layers (this includes the multiply, screen and overlay layers), move the opacity of the new layer to 0, and slowly turn it up until the image as a whole looks good. This will almost never be at 100%. Then, if certain objects seem under saturated, I can turn back on those color layers and adjust their opacity until it looks good.
 * One technique I've found that sounds like brilliance, but only works under certain specific circumstances is to select the object I want to color on the grayscale layer, then create a new layer from that selection. I can then adjust the levels to wash out everything but the shadows, while bumping up the darkness of the shadows. Then, by creating a layer mask from this grayscale layer, clearing the layer and filling it with the shadow color, you can get a shadow color layer that perfectly maps to the shadows on that object. Be careful, though. Generally, your shadow colors tend to extend beyond the edges of the actual shadows a bit, and this doesn't accomplish that. It usually only works on small images, or in small regions, and only when there is a low contrast between shadows and highlights.
 * A great way to control spilling of colors is to create your base color layer, then use that layer's alpha channel to create a mask for your shadow layers. This will let you work without inadvertently spilling shadow colors onto other objects.
 * Keeping your shadow colors the same or very similar is the key to keeping the objects tied together.
 * Using a small, soft brush is better for tracing the edges of an object than a brush with hard edges. Once you've gotten an outline, you can switch to a harder edged brush to fill in the rest. One trick for this is to switch to the pencil once you've got your outlines done, and go over the inside edges with the pencil tool. This ensures that the inside edges have no anti-aliasing or feathering, meaning once you've gotten all the way around all the edges, the bucket fill tool will do the rest of the work for you.
 * When trying to restore a black and white photograph without adding color to it, you can actually colorize it, then fade the colorizing out just until the colors themselves are not noticeable. This will increase the contrast of the image subtly, without generating artifacts or loosing detail the way directly adjusting the contrast does.
 * Have fun! If you find the work tedious, you're going to do a poor job at it. If you ever find yourself wishing you could just be done with it, save your file and find something else to do. Eventually, the urge to return to it will hit, and you can come back refreshed and re-energized.