maybe just a few zebra stripes????
Posted 29 November 2005 - 12:29 PM
Posted 29 November 2005 - 12:51 PM
Hi folks, I'm brand new to this stuff so please bare with me. Shooting digital video in my house during certain hours of the day, it is almost impossible to get rid of all the zebra strips showing on my LCD. I want the most professional looking footage I can shoot. (I don't have a project going on right now I'm just trying to learn how to get the shots when I want them) My question is: Is it acceptable to have a few items in the frame overexposed (zebra stripes) or is the goal always to rid of "ALL" stripes. I'm just having a tough time getting rid of all of them and then still getting good exposure on the rest of the shot. I've tried stopping down and/or increasing shutter speed until stripes are gone but then the rest of the frame is too dark. Should I buy ND filters or will this give the same results as stopping down too much. I don't have any shades to reduce light in the family room where we shoot....and I just want to work with what light comes in and deal with it somehow with the camera "to learn camera techniques". Sometimes, the overexposed area is an object that can be removed, like a magazine or picture frame but I just want to see what a professional would do in these cases. Thanks.
What camera do u have?
I am asking you this cause in some camera's the Zebra pattern is adjustable.
Or others have two Zebra patterns that u can adjust.One for the 100% of signal (white) and a lower zebra for other percentage of the signal,(like 70-75%) usefull for skin tones (white caucasian skin exposure).
The zebra isn't recorded in the tape if this is what you mean, and u should avoid it only if it's set at 100% of the signal and you see it on a face for example, wich means that you are overexposing the face.
For example 100% zebra can be seen on a cloud, (I hope that psychiatrists don't read this)
in a white table, white walls, highlights of a wet face etc.
It helps you adjust your exposure, or warn you if you are overexposing too much.
Try to use your eye, if it looks good for you, ignore the zebra pattern.
Edited by Dimitrios Koukas, 29 November 2005 - 12:51 PM.
Posted 29 November 2005 - 01:08 PM
Posted 29 November 2005 - 01:22 PM
Properly calibrate the monitor using your cam's colorbars; if you need to know how, refer to:
Having done the above, how does the video look on the monitor? How does the exposure look in general? Overexposed? Or are only small areas of the frame overexposed?
If it's generally overexposed (large areas of the frame are blown-out to white with no detail), turn off the cam's auto-iris and use the cam's manual iris to reduce the exposure or adjust the lighting in the scene.
If only small areas of the frame are overexposed/blown-out, that's not necessarily a problem. If the overexposed areas/object don't contain "useful" information -- in other words, you don't care if they have no visible detail or texture -- it's usually OK for them to be overexposed. It's more an asthetic issue than a technical one.
(For example, if you're shooting in a rush, rush broadcast TV news environment where you have to hand over your footage for immediate broadcast, and even then if it's really newsworthy, no one cares if parts are overexposed -- the station's equipment will auto-clip the highlights and the audience will get their baby-slasher story, the station's ratings will go up, and everyone's happy.)
But if the overexposed areas contain useful info -- or would contain useful info if they weren't blown-out -- then there are almost limitless techniques you might use to reduce the exposure only in those areas or overall.
This website among many others, hundreds of books on lighting & cinematography, university classes, working as an apprentice on real shoots, and your own testing, testing, testing are typical ways to learn about these techniques.
Many of these techniques involve approaches which are free or nearly free, and many of these are extremely low-tech -- often the best approaches are free/low tech, too!
For example, casting a shadow needn't be difficult or expensive. You already know how to cast a shadow -- just think about it a bit and you can probably improvise something to cast a shadow onto the desired area in a few seconds or minutes. A hat rack might work, or an assistant holding a piece of cardboard/foamcore, or a C-stand holding a black flag, and so forth.
To answer one of your questions, an ND filter will make the entire scene darker, which may or may not be the effect you want. It may have undesireable consequences -- such as causing a cam's auto-gain circuit to boost the picture and possibly cause noise (if so, turn off the auto-gain). Of course, an ND filter can be extremely useful in situations related to its intended use, but that's true of any tool. A "graduated ND" (or "grad") filter reduces exposure in part of the frame only. The trick is knowing whether a tool is required, and if so, how to use it.
Another tool: A polarizing filter can reduce or eliminate a hot-spot caused by reflected light.
Noticed how I haven't mentioned zebras since the first sentence?
If your camera's zebras are set to approx. 70-80 IRE they can be useful to indicate that exposure level on, for example, typical Caucasion skin and objects of similar color/tone. It's usually OK if this zebra indicator appears on part of a person's face, but if the indication is overall on a face the lighting may be too flat (no/few shadows, no "modeling") -- but this is an asthetic issue; you might like flat lighting. You may find flat lighting makes a person's face wrinkles less noticeable -- sometimes good for woman and not for a man -- it's your choice.
If your camera's zebras are set to 100 IRE or higher they're indicating what part of the frame is blown out with little or no detail. In video, once something is 100 IRE or so it's gone for good; you usually can't bring it back later. As discussed above, that may or may not be a problem.
Trust you eyes. If possible, use a calibrated CRT monitor. If the picture looks good to you, if it's pleasing, and if important parts of the frame aren't too over (or under) exposed, you're good to go. Or, adjust to your taste or the technical/asthetic requirements of your clients/audience.
I hope the above info is helpful.
All the best,
- Peter DeCrescenzo
Edited by Peter DeCrescenzo, 29 November 2005 - 02:00 PM.
Posted 29 November 2005 - 04:06 PM
Posted 29 November 2005 - 04:58 PM
... I also like the Idea of turning off that feature and using a calibrated CRT monitor and just eyeballing. ... I have a seven year old Hewlett Packard pavilion computer monitor that came with a computer we bought packed away somewhere, I wonder if this would serve the purpose?
Most monitors designed for computer use don't work directly with video sources such as a camcorder. Adapting a computer monitor to be compatible with NTSC or PAL video might not be inexpensive and the results might not be as good as simply using a TV monitor designed for video.
Although a "pro" video monitor is desireable, a TV monitor can substitute in a pinch. Whatever monitor is used should be calibrated. As described in the article at the link above, you can calibrate a monitor which doesn't have a "blue only" switch by using a piece of full CTB gel or Wratten 47B filter held over your eye. It's best to do the calibration using SMPTE "split" bars because they have the NTSC "pluge" bars in the lower right corner and the upper/lower bar segments for adjusting chroma (color) and phase (tint).
The THX calibration feature on some "Hollywood" DVDs can also be used to adjust a TV/monitor fairly accurately, too.
BTW, I suggest both "eyeballing" your video via a CRT monitor as well as also using your cam's zebras. Each has its own value in evaluating your video. Also, once you've trained your "eye" to compensate for the deficiencies of your cam's built-in LCD screen/VF, they can be semi-useful, too.
Once you get comfortable doing the above, you might also research waveform monitors and vectorscope monitors, some of which are now software-based instead of external hardware instruments. For example, some editing software include these features, and there is standalone WF/VS software, too. But for now, get comfortable with using your cam's zebras and an external video monitor.
- Peter DeCrescenzo
Edited by Peter DeCrescenzo, 30 November 2005 - 01:07 AM.