Purpose of Color Bars...greenspun.com : LUSENET : Shooting DV Films : One Thread
Hi, I'm going to ask what I assume is a pretty basic question, but being a video newbie, I figure I should ask it/them:
What are the purpose of color bars? I read in the other "color bars" post about official STMPE color bars and wotnot, but why are they there and how do they work?
I assume that you would display color bars on your television or monitor and match it to an actual printed color bar sheet to calibrate your TV.monitor. Yes or no? What's the purpose of having them on your camera?
Basically, why do you use color bars, how do you use them, and how do you get access to them?
-- Dave Lee (email@example.com), November 16, 1998
I do not own any digital recording equipment yet, but I do have several years of experience directing and editing commercials. STMPE color bars are a standardized color bar pattern that will appear as a specific pattern on a waveform monitor and a vectorscope. You should ALWAYS lay down bars on the front of a tape so you can match the camera's "idea" of what true colors are, to your editing system's "idea". Of course if you don't correctly white balance or filter your camera for the scenes you shoot, then throw that out the window. Once you match these on a vectorscope and waveform it really doesn't matter what your monitor looks like because they are identical electronically. TO properly set your monitor so you can see these actual colors, most professional monitors have either "gun controls" or a "blue button" With gun controls you turn off the red and green guns with color bars on the monitor. With a "blue button" simply push the "blue button" The result is a black and blue alternating pattern. Adjust your hue control until the black bars and the blue bars match each other corresponding bar in color and luminance. Even though the XL1 doesn't have STMPE bars still lay bars down on the front of each tape. While the bar patterns will not be as exact as STMPE bars, they will still get you closer to actual color matching than eyeballing it. Trust me, your eyes can see whatever color they want, you will drive yourself mad trying to eyeball your monitor to a correct solor bar sheet.
-- Chad Denning (LONO915@aol.com), December 01, 1998.
Just laying down camera-generated color bars at the start of a shoot won't tell you much, except that the camera is generating color bars and that the monitor you are viewing them on is calibrated.
To really see if the camera is properly set up, you must shoot a color bar chart (an actual card you hold in your hand with color bars printed on it). Shoot it under the lighting and with the white balance settings you plan to use. This will not only let YOU adjust your settings in the field, before you shoot, but will clue your editor in on any post production color correction that will be required.
Regards, Doug Graham Panda Productions
-- Doug Graham (firstname.lastname@example.org), December 17, 1998.
Color bars are extremely important to working with any format of video. Remember, the VX-1000's color bars are not SMPTE sinc. These bars will let you adjust close to SMPTE color on a monitor. Adding bars and tone (if possible) to the head of your tape offers an air of professionalism.
-- Smith (email@example.com), December 22, 1998.
The purpose of color bars on the head of each and every tape is so that the machine that plays it back either in editing or on air can be set for standard playback. It is possible that head wear, mis- alignment and so forth, can cause poor recording. By playing back the bars, weather SMPTE, split field, or single field, doesn't matter, and then adjusting the proc amp controls on the play back machine, using scopes it can be set to bring a sub-standard recording back to standard playback. When set up right, we can do match frame edits using different brand machines in different edit facilities. The key is the bars.
The standard in the broadcast industry is one minute of bars recorded at the head of field tapes. In addition to providing enough bars for propper playback setup, this also guarantees enough leader before good footage. If there is any manufactured defects on the tape, they will probably be in the first or last 30 seconds where the tape was cut to squeeze into the shell. Also, this guarantees more than enough leader for pre-roll. On the master, the industry standard, as noted in the International Teleproduction Society Handbook of Recommended Standards and Procedures, is 10 feet of blank leader (that probably works out to 20 or 30 seconds on most tape formats), 60 seconds of color bars with 1,000 kHz audio tone, 10 seconds of slate and at least 1.8 seconds of black before the program starts. In our facility, which produces network programs among other productions, we include 10 seconds of black between bars and slate and another 10 between slate and program. In my former life I worked in the tape room of a large market TV station and also switched air. Lots of leader and lots of bars and tone always made me happy!
Ken Smith Morning Star Media Group e-mail: firstname.lastname@example.org on the web: www.morningstartv.com (check us out)
-- Ken Smith (email@example.com), January 09, 1999.