Connectix QuickCam Frame Rates

    Connectix QuickCam Frame Rates

    Connectix QuickCam Frame Rates

    On Wed, 7 Dec 1994

    explained:

    The QuickCam frame rate is determined by several factors:

    Brightness setting (determines how long the CCD is allowed to gather charge for each frame)

    Size of the image (when running certain applications, like the ones Connectix supplies)

    Available processor bandwidth on your Mac (depends on what program(s) you’re running on your Mac)

    Maximum Mac serial port speed (depends on Mac model)

    The actual frame rate you get will be the minimum of the frame rates

    allowed by these constraints. (The chain is only as strong as its weakest

    link). The formula is something like this:

    framerate = MIN(1/exposuretime, 1/imagesize, bandwidth, portspeed)

    exposuretime is an exponential function of the brightness slider setting:

    if the slider is a scale from 0 to 100, each 10 units is about a doubling

    of the exposure time.

    imagesize is in pixels — I think.

    Sometimes when the exposuretime is

    really high, my QuickCam frame rate seems to depend on the *linear* size

    of the image: twice as high, half the frame rate (rather than 1/4 as

    you’d expect)

    bandwidth is proportional to the processor’s Speedometer rating for

    “general” tasks. As I said, it depends on the application. CU-SeeMe, for

    example, chews up a lot of time doing compression, deompression and

    audio.

    portspeed depends on Mac model and sort of (but not always) follows the

    processor speed.

    On 4 Jan 1995

    said:

    I believe this has been mentioned on the list before, but it deserves

    re-emphasis.

    Unlike most cameras, the Connectix QuickCam does not have an

    “auto-iris,” (i.e., the ability to automatically adjust to available

    light).

    Although there are certain advantages to this, a problem results

    with flourescent light fixtures, which apparently cycle in the amount of

    light they give off, producing oscillations in the brightness of the

    displayed video image.

    Aside from the annoyance of the oscillations, this

    behavior defeats the compression algorithm by causing the entire image to

    change with each frame (in the worst case), so frame rates drop

    dramatically.

    I just saw this in action, dropping what should have been 10

    fps or so down to 1 fps.

    The only solution I can think of if you are in

    this situation is to smooth out the flourescent cycle with some other light

    source.

    Even if you add in the price of incadescent bulb and lamp, the

    Connectix is still a good deal.

    Note also that auto-irises are not without

    problems, as slight changes in the subject matter can change the amount of

    light reaching the lens, causing it to open or close, and introducing

    spurious changes in parts of the image that have not changed at all.

    Have you found errors nontrivial or marginal, factual, analytical and illogical, arithmetical, temporal, or even typographical? Please let me know; drop me . Thanks!

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    Connectix QuickCam Frame Rates

    Connectix QuickCam Frame Rates

    Connectix QuickCam Frame Rates

    On Wed, 7 Dec 1994

    explained:

    The QuickCam frame rate is determined by several factors:

    Brightness setting (determines how long the CCD is allowed to gather charge for each frame)

    Size of the image (when running certain applications, like the ones Connectix supplies)

    Available processor bandwidth on your Mac (depends on what program(s) you’re running on your Mac)

    Maximum Mac serial port speed (depends on Mac model)

    The actual frame rate you get will be the minimum of the frame rates

    allowed by these constraints. (The chain is only as strong as its weakest

    link). The formula is something like this:

    framerate = MIN(1/exposuretime, 1/imagesize, bandwidth, portspeed)

    exposuretime is an exponential function of the brightness slider setting:

    if the slider is a scale from 0 to 100, each 10 units is about a doubling

    of the exposure time.

    imagesize is in pixels — I think.

    Sometimes when the exposuretime is

    really high, my QuickCam frame rate seems to depend on the *linear* size

    of the image: twice as high, half the frame rate (rather than 1/4 as

    you’d expect)

    bandwidth is proportional to the processor’s Speedometer rating for

    “general” tasks. As I said, it depends on the application. CU-SeeMe, for

    example, chews up a lot of time doing compression, deompression and

    audio.

    portspeed depends on Mac model and sort of (but not always) follows the

    processor speed.

    On 4 Jan 1995

    said:

    I believe this has been mentioned on the list before, but it deserves

    re-emphasis.

    Unlike most cameras, the Connectix QuickCam does not have an

    “auto-iris,” (i.e., the ability to automatically adjust to available

    light).

    Although there are certain advantages to this, a problem results

    with flourescent light fixtures, which apparently cycle in the amount of

    light they give off, producing oscillations in the brightness of the

    displayed video image.

    Aside from the annoyance of the oscillations, this

    behavior defeats the compression algorithm by causing the entire image to

    change with each frame (in the worst case), so frame rates drop

    dramatically.

    I just saw this in action, dropping what should have been 10

    fps or so down to 1 fps.

    The only solution I can think of if you are in

    this situation is to smooth out the flourescent cycle with some other light

    source.

    Even if you add in the price of incadescent bulb and lamp, the

    Connectix is still a good deal.

    Note also that auto-irises are not without

    problems, as slight changes in the subject matter can change the amount of

    light reaching the lens, causing it to open or close, and introducing

    spurious changes in parts of the image that have not changed at all.

    Have you found errors nontrivial or marginal, factual, analytical and illogical, arithmetical, temporal, or even typographical? Please let me know; drop me . Thanks!

    |

    |

    |

    |

    |

    |

    |

    |

    This page

    is

    1993-2006 by ,

    via the Creative Commons License. Questions and comments? Send

    to the Geek Times Webmaster. (Domain and web content hosting at .)

    Leave a Reply

    Your email address will not be published.