The difference between bright and dark parts of an image.

"Never Twice the Same Color" or possibly the National Television Standards Committee, which refers to the standard for analog televisions in North America and some other countries. Two other key standards are PAL, used in Europe, India, and elsewhere and SECAM, used in France and Russia.

Generally, you want the viewer's eyes to focus on a part of the screen. You can do this by motion or lighting. Let's talk about the lighting part. If something is brighter than the rest of the shot, you will pay more attention to it. Sounds simple, but a lot of tools can be employed to do this in subtly different ways.

To focus attention on a subject, you don't simply have to add more light on a subject. You can remove light by using a flag to reduce the light hitting the background. You can also use barndoors, scrims, silks, and foil to reduce the light spilled onto any area you don't want light to go. If a subject must wear a white shirt, you can use some diffusion material in an open-end frame to reduce the light on the shirt without creating a hard edge that will be seen. We'll discuss problem colors later.

If you have bright or shiny objects in the frame, see if you can remove them or cover them. Our eyes are drawn to these things, which is not always desirable. If something metallic must be in the frame, you may use dulling spray on it, which washes off, or you can put Scotch tape on it, which will not be visible on video. You can also change the position of lights to reduce reflections.

If you have the time, you can be very precise with flags to take light off of an area. Several different shapes of flags are available for this. For my budget, I more often just create a shape with black foil.

Sometimes too much of a good thing is bad. For instance, if your subject is in a large open area and you don't want it to look like your subject is in limbo, you will need to add a background light to reveal the background. If the background is a wall, break it up with a cookie and let the light have some variation, instead of lighting it uniformly. Use a background light sparingly. You don't want to draw attention away from your subjects. If the background is too bright, you can use a flag to create a shadow along the wall that makes the background darker and more pleasing.

Most of the time, you will be lighting people, and more specifically, faces. The basic concept is this: focus attention on the subject and make them look more or less attractive and more or less dramatic, bland, happy, sad, scared, etc, by controlling light and shadow.

Try to make the light hit people at angles other than head-on or directly from behind (unless you are shooting silhouettes, but that's a very special case.) If the light hits the subject at a 30 or 45 degree angle, you will get much more interesting modeling.

A heavily-used technique for lighting people consisting of a key light, a fill light, and a back light. The fill light doesn't have to be a light at all. It can be a reflector. Three-point lighting looks good because you can control the quality of the shadows using the fill, and you have separation of the subject from the background using the back light, giving a beautifully modeled image.

The position of lights has a huge affect on the look of the subject, especially people. When people are lit from below, they have an eerie or sinister look to them, which can be used to your advantage. You can light from high above if you shoot a person wearing glasses, to reduce the glare on the glasses. You don't want to key from too high above because you can't get good modeling on a face. On the other hand, if you want to de-emphasize a large nose, you can move a light higher to reduce the size of the shadow cast by the nose. A light directly above and just in front of the person can create dark eyes, à la The Godfather.

You can sometime use spill creatively to provide fill for a key light. You can bounce spilled light back onto a subject with a reflector, a wall or a ceiling. You can also use spill light to light a background, if the background is not too far away.

You can bounce light to your advantage. For instance, having the subject reading a book and lighting the subject from above will bounce light off the white pages of the book and create a soft light that illuminates the face. This can be manipulated to simulate a light source from below which could look eerie, as when a wizard is reading from a book of spells. Two people dancing, if one is wearing white, can effectively provide the same effect. A white or light colored table can produce the same effect, as in an interrogation scene.

Windows can be excellent sources of light for shooting an interior. They can also ruin a shot if not controlled. Here are some ways of controlling light that comes through windows.

Black organza fabric, or the black netting used to make widow's veils. You can stretch these over windows to block some of the light. If you don't focus on it, it won't be seen. If you need less blockage, you can use bridal veil material, or white organza.

White sheet. If a window isn't visible, you can use a white sheet or a silk, but it will give you soft light, which you may not want. If you want the light to be hard, don't diffuse it.

Tracing paper. If you want soft light, and you don't need to see through the window, another option is to put tracing paper on the window. I've never done this, but I know it's used.

ND gels. Neutral Density gels. An expensive option, but more precise. You can precisely control the amount of light coming through with these large plastic sheets calibrated to reduce light in specific amounts that correspond to stop exposures.

CTO gels. Color Temperature Orange gels. You can also change the color temperature of the light coming through to "warm it up" by using these orange gels. They come in different strengths from full CTO to fractional strengths like 1/2, 1/4 etc.

CTB gels. Color Temperature Blue gels. Nobody says that daylight in a film must come from the sun. You can use a tungsten light outside a window and put a CTB gel on it or the window.

Nocturne fabric, or opaque white fabric. At some point, you will probably want to block most of the light from a window. This will do the trick. This, and organza are found, not surprisingly at fabric stores.

Typically, you should manually set the white balance by filling the frame with a white object, but you can also use available presets, usually, one for daylight and one for tungsten. One useful time to use the tungsten preset is when taping a concert that employs colored lights. With some cameras, such as the Canon XL1s you may be able to use Auto White balance when you are shooting with commercial fluorescent lights.

Just because you can control everything to be realistic doesn't mean that you have to. You can mix lights of different temperatures for stylistic reasons. You can choose to have light from a window be more blue than interior light. You can "warm up a scene by adding gels to a light, or by adjusting the white balance by using a blue object next to a white card when you white balance. You can make this more blue by replacing the blue object with a yellow object.

These lights are notoriously bad for shooting video and film. They come in many different temperatures, but the primary color that shows up on video is green, especially if you are mixing light from them with professional lights. In such a case, you can't use the white balance on the camera, because you will have different temperature light coming from different sources. Consumer fluorescent lights and their shades are more likely to change color with time, so adding a gel to correct the color is not always reliable. If you want to experiment, you can green gels to correct a tungsten light to match commercial fluorescent lights, often 4500K. Don't forget to white balance when you have your lights set up.

If you want to create realistic images, you should use motivated sources, which means that the viewer must know or infer what or where the source of the light is. The light source does not have to be visible, but it often is, at least at some time. When you have practicals in the scene, be sure that the light appears to come with them, even if you are primarily lighting from another fixture. For instance, if you show a lit desk lamp, don't have shadows going toward the lamp, unless those shadows are motivated by a stronger light that the audience is aware of. It isn't always possible or desirable to have motivated lighting. Shooting at night is a commonly accepted exception. Part of the reason is because of the difference between our eyes and video. We have to put some ambient light into night scenes because otherwise, it would be too dark on video to see the actors or the environment.

Better video cameras have zebra patterns to help you detect over-exposure. You should use it. When it detects that part of your frame is over a specified exposure (from between 70 to 100 IRE), it will show a striped pattern in the viewfinder. In general, you do not want to over-expose any part of the frame because then you cannot get back any image information from that area. In reality, you can't often correct this while shooting, but you should still make a conscious decision to allow a part of the frame to over-expose so that you can see the part of the image that matters most.

Be wary of shooting with colored wall, because they will reflect the color onto subjects that you might not notice until later. Avoid bright red with video because NTSC has problems displaying it, causing the color to appear to be alive and "crawl." More important still, avoid shooting with white walls in the background. They look awful and draw attention away from the subject.

Definitely avoid bright red clothes because of color crawl problems. Avoid white clothes if the person wearing it has dark skin; it will be hard to get an even exposure in that case, and harder to see the subject's face.

Shooting outside during the day is nice because you don't have to lug around expensive lights and worry about electricity. It's also difficult because you don't have any control over the sun and clouds. The quality of your light can change in just a few minutes.

If you have problems with the sun coming in and out between clouds, try to move your subject to a shady area, reducing the variation in the light. If this is not possible, you can diffuse the light by using a large diffusion screen supported by C-stands. Make sure that you put sand bags on the stands to keep them from toppling over.

When the sky is clear, the sun is the ultimate hard light source. You can soften it with diffusion. You can also bounce some light onto the subject for fill using a white, silver, or gold reflector, depending on whatever look is more pleasing.

Shooting in the shade is important if you don't have other lights or reflectors available. Otherwise, the brightness and hardness of the sun will produce undesirable contrast ratio that might look bad on video (and even film). If you cannot place your subject in the shade, you can place your subject so that the sun is behind them, giving them a nice backlight, putting their face in flatter, soft light and reducing the amount they have to squint.

When the sky is overcast, the entire sky is the ultimate soft light source. You won't be able to effectively bounce much light from it with a reflector. The shot will be relatively low contrast.

ND filters should often be used when shooting outdoors. You can limit depth of field by allowing the lens aperture to be larger. This will give you more of a "film look" and it will focus attention on your subject (assuming your subject is in focus!) Without an ND filter on a sunny day, you will be forced to shoot at extremely high f-stops outdoors (f11 to f16), resulting a very deep depth of field. Often this huge depth is what makes video look bad. Moreover, shooting at very small apertures can degrade the image, due to diffraction effects at small apertures. See the appendix for more information.

Use a polarizer filter if you want to reduce reflections from glass or other shiny objects. You can also use a polarizer to make a blue sky more blue because the polarizer can absorb light reflected by particles in the air.

If you shoot on green grass, surrounded by green trees, you will get green light reflected onto your subject. You can control this some by having a neutral colored blanket under the subject, out of frame. This is subtle, and may not be a serious concern. Just know that it is an option.

If you want to make a more pleasing exterior shot, don't shoot at mid-day if the sky is clear. The lack of shadows makes things look unpleasing.

Remember that as the day progresses, the position of the sun (and resultant shadows) will change, making it more challenging to match shots. Also, you will need to adjust reflectors and diffusion to keep up with the sun.

No discussion on exterior shooting would be complete without bringing up the term magic hour. This is the time near dusk and dawn when the light from the low sun, or non-visible sun, makes everything look golden and beautiful with a soft quality of light. The duration of this time depends on the time of year and the latitude of the location. With the sensitivity of video cameras, you can extend this time but watch out for shots that don't match previous shots. This works best when you shoot scenes in the same order they will be seen on the screen.

You should avoid most automatic settings on your camera, but in one case, you can use them as a convenient light meter when light conditions change. Simply switch to automatic mode and note the suggested exposure and use that to compare that to subsequent readings. Make sure that you use the same framing, and that you frame the area of interest when you take the measurement. In other words, if you are shooting someone and 80% of the frame will be the sky and 20% will be the subject, zoom in until your subject takes up the majority of the frame. Use this framing for your measurements, then zoom back out for your shooting frame. Be very careful to avoid changes in shutter speed as this will affect the look of your video. It's best to keep your shutter speed consistent from shot to shot.

You will need light, so try to make the lighting motivated. Still, you can add some ambient light with subtlety, and most people will accept it when they see it. Viewers are accustomed to this. I find it useful to add some background lighting to foliage so that subjects are not surrounded by black.

Moonlight is simulated by adding blue gels to tungsten light. Be sure to white balance before you add the gels. The trend in films is to make night shots less blue. I think that low budget films are probably best served by using more blue than expensive films because we can't afford to create a convincing world on our budget. If you don't use enough blue, it will look like you shot under artificial light instead of moonlight. Depending on your tastes, you might try using 1/2 to full CTB gels for moonlight, and you should underexpose about a stop.

I'll mention that shooting day-for-night is an option that you can read about, but since I have not successfully done this, I can't help you much.

Shooting in a car is challenging, whether by day or night.

The biggest challenge during the day is that if you are shooting from the side, the driver will be backlit, or lit from behind. If you open the aperture to allow more light into the camera, the images in the window behind the driver will be blown out and look amateurish. You can mitigate this by reducing the light from the window with gels or by increasing the light in the car. On a bright day, you should rent a battery-operated HMI to light the subject from inside the car. Be sure to diffuse the light so that you do not get strong shadows indicating the direction of the light source. If you can't afford an HMI light, use tungsten battery lights and put full CTB gels and diffusion on them. This will reduce the light output tremendously, but it's better than nothing.

Even in a car, the lighting should be motivated, but this is another case where viewers are used to unrealistic light levels. At night, you can motivate the idea of lights coming from an instrument panel. If you show that the panel lights are orange, for instance, you can use a good amount or orange light to light the interior. Don't get too wrapped up over this, though. As I said, viewers are very accepting of this unreality.

If you need to shoot through a car window and you want to see through the glass as much as possible, use a polarizer filter on the camera lens, This removes polarized light and can reduce glare on the auto glass.