To celebrate 100 years of color imaging, from hand painted frames to video formats, let’s take a closer look at what color means to video producers in post.
One hundred years of color development has produced stunning color representation in our moving media. In the past, manipulating color images has come with its burden of being time consuming and chock full of restrictions. Today, video not only needs to fit in finite storage spaces such as Mini DV tapes, DVDs, hard drives, etc., but it also needs to travel through limited bandwidth, such as across the Internet or via satellite transmission. This electronic method of acquiring and distributing video restricts file sizes. Therefore, compressing video is a necessity and can affect the amount of color information in the resulting image.
Let’s look at why we would want to change the color our camera has recorded, some of the technical details of how our camera compresses color, and a few of the techniques we might employ to correct or enhance the color in our image.
When to Change Your Color
There are two dominant circumstances in post that would make us take the time to change our video’s color:
1. If we need to correct color in our image that has not been shot the way we intended, or
2. If we want to stylize our image.
Probably one of the most common problems when dealing with color is correcting a poorly white balanced shot. We have all done it: forgotten to manually white balance our camera or left it on a setting from a different location and lighting set-up. Though we never advocate consciously deciding to “fix it in post,” there are times when you will make these mistakes in the field or studio. Or, you may choose a stylized look for your work, such as the Coen brothers did in their film O Brother, Where Art Thou? (2000) or David O. Russell did with Three Kings (1999). Keep in mind, these directors most likely got their look “in camera,” (e.g., choosing a certain film stock and film process), but it can also be done in post. You also might want to remove the color altogether or create a colorized dream sequence.
What is the Make-up of Color?
The human eye can identify more subtle differences in brightness than it can in color. Thus, engineers have developed modern video compression methods that leave out elements of color that we do not usually perceive, leaving more room for detail in luminance or grayscale level and smaller files sizes. This is not a perfect science-it’s more of a rounding off-but it does get the file size of video, along with other forms of compression, much smaller than uncompressed video.
Here is an oversimplified explanation of video color compression. A digital video signal converts from its original RGB color space into three main signals: a luminance signal and two Chroma (color) signals. Together, these three signals make up a new color space best known as YUV (although, technically speaking, YIQ and YCbCr are also commonly used in NTSC video). What’s important to note is that the luminance (Y) signal holds most of the video signal detail, because it’s made up of the total luminance of the original RGB image space. The Y signal is basically your black and white image and the two Chroma channels help fill in the color, although, with not nearly as much detail as the luminance signal. Combined, these three signals make what we perceive as a full color picture. Yet, the image still needs to be sampled before the compression is complete. Because the human eye can tell much more subtle differences in luminance, this component is fully sampled while the two color variables are sampled less.
When an image is digitized, usually within the camera these days, groups of four video pixels are analyzed and samples are taken. With a 4:2::2 color sampling used with Digital-S (from JVC), DVCPRO-50 (from Panasonic), Digital Betacam, D-1 and D-5, all four luminance pixels and only two pixels of each Chroma signal are sampled. This makes the file size much smaller than full, uncompressed 4:4:4 video. With a 4:1:1 signal used by DV, DVCAM and DVCPRO, all four of the luminance pixels are sampled while only one pixel of each Chroma signal is sampled. This makes the file size roughly half the size of 4:2:2 but the color reproduction is not as great. The average human eye, in most circumstances, cannot tell the difference, but there are times when this could be a hindrance to an editor.
Having more color information helps when an editor wants to make large alterations in the color space of an image in post. A good example is with green/blue screen work. Though technology has made it easier to achieve a good looking key using a 4:1:1 color image, say, from a Mini DV camera, results will be more pleasing with an accurately keyed 4:2:2 image or a 4:4:4 image. The same principle goes for any extensive color correction.
How to Become a Color Expert
There are many tools to learn the art and craft of color correction and enhancement. Some are free on the Internet, others come in books, DVDs and in the form of online tutorials and there are even multi-day classes available.
Though their names may differ, here is a sampling of the color tools found in most current editing software Effects bin or folder.
- Auto Color Drop this filter on your poorly white balanced shot and you’ll get a greatly improved image. Although not perfect, it’s a great starting point to correct your white balance woes.
- Hue, Saturation & Luma Adjusting This filter alters the grade (or angle), intensity and brightness of color, by using a series of sliding bars for fine tune fixes.
- Three-Way Color Correction This is the granddaddy of color correction and alteration. There are numerous tutorials produced to aid in the use of this one tool. It allows precise control over hue, saturation and brightness in highlights, midtones and shadows.
- Waveform Monitor A digital oscilloscope (device that measures and displays wave forms and voltage) that displays the luminance information of video.
- Vectorscope A digital oscilloscope that graphically displays the Chroma, or color, portion of video.
These are just a few of the filters and tools that will not only let you fix color mistakes you made while shooting but can let you enhance the color of your moving image to further your storyline. With these powerful tools, your knowledge and imagination are the only limits to the limitless color possibilities.
Morgan Paar is a nomadic producer, shooter and editor currently making documentaries in South America.