taking pictures off the tv

[basicbill]

Hi everyone,
New forum member.
I shoot with an Olympus C-8080 digital. Pretty good camera for my use.
I find myself needing to take pictures off the tv and I continually get a moire pattern that wrecks the image.
The tv is a HDTV, LCD type.
With the proliferation of lcd tv's and digital cameras, it's remarkable that there isn't much information on this particular problem.

All my shots have been tripod with remote so that's not the issue.

Anyone do this successfully? and how?

tia,
basicbill

[mtbbrian]

I don' know what shutter speed you are using, but I would experiement around 1-/60th of a second.
That "should" be the best shutter speed for what you're trying to do.
Keep in mind, the picture your camera takes won't be the same as what you see from the TV.
I don't know how to explain it, but you will always get patterns or lines that come from the screen.
Good Luck!
Brian

[brmill26]

The explanation is because the TV is constantly refreshing the picture via scan lines, usually top to bottom left to right. The refresh rate is usually around 60 hertz, so shooting it at 1/60 gives the best chance for you catching a single scan frame.

If you're really needing to take images off TV so much, why are you using a still camera? It would be far easier to hook up a camcorder, or even easier, run the cable straight into your computer via a tuner card. Then you could use software (even Windows Movie Maker will take stills from video) to pause the video and capture whatever frame you wished - that would eliminate the scan and moire pattern.

[basicbill]

Thanks Brian and Brad.
Unfortunately the camcorder/tuner card option is no good for me. (old guy with not much money).
My attempts thus far have been at very slow shutter speeds.... 1/2 .... 1/1.3 .... 1 ..... etc. Any slower and the picture is just too dark. (aperture at 4 to 5.2).
Your explanation is good regarding the moire. Interference lines seem likely if the camera is processing 60 scans (1 second shutter).
I'll try again at 1/60 and open it up all the way.
I'll let you know how I make out.

(all pictures are attempted after 'freezing' the tv image)

thanks again.

[freygr]

The frame rate is thirty frames a second so simple math is shutter speed is 1/30. You can also tell wither the shutter is slow or fast just by looking at the photo. A slow shutter will have a bright line in the raster, a fast shutter will be missing part of the image. The percentage of error can be calculated off the photo without any problems just by measuring and simple division.

The best way is to use a video capture card with a computer much cheaper than using any kind of camera as you can purchase a USB video capture device for las than a $100 now days. And with the software you can pull out just one frame from the video file, and it's much easier to.

[brmill26]

Freygr - don't confuse NTSC video frame rate (29.97 frames/sec) with a video monitor's refresh rate. They're two very different things.

Excerpt from Wikipedia:

Televisions

"When the cathode ray tube was developed in the 1920s, technology limitations of the time made it difficult to run monitors at anything other than a multiple of the AC line frequency used to power the set. Thus producers had little choice but to run sets at 60 Hz in America, and 50 Hz in Europe. These rates formed the basis for the NTSC (60 Hz) and PAL & SECAM (50 Hz) sets used today. It was widely perceived that this accident of chance gave European sets an advantage, because the slower 50 Hz refresh rate gave the CRT time to scan more detail. However this rate also introduced more flicker, and exacerbated the negative effects of interlace, so sets that use digital technology to double the refresh rate to 100 Hz are now popular.

Another problem with 50 Hz standards is that motion pictures cannot be easily presented in the typical 24 fps rate used for 35 mm film. These must be accelerated by 4% - with an accompanying slight shift in the pitch of the audio. NTSC sets can display both 24 fps and 25 fps material without speed shift by using a technique called 3:2 pulldown, but at the expense of introducing Telecine Judder.

Unlike computer monitors, HDTV and some DVDs, analog television systems use interlace, which increases flicker compared to a progressive scan image at the same refresh rate. The amount of extra flicker is largely dependent on the content of the image, and the brightness of the screen. Many newer televisions are flicker-free."

Full text: http://en.wikipedia.org/wiki/Refresh_rate