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Thread: White spot in almost every picture

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    Default White spot in almost every picture

    Hi anyone expert ,my digital camera is starting to have white spot or a dot of white light at the same position of almost every picture that I shoot.
    Is there anyone with this problem with your digital camera? Is it the camera lens faulty, I have tried cleaning the lens but no different.Can someone help to explain.I only used for 2 months only. Thank you.

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    no expert , but It could be a hot pixel, that is a transistor ( millions of them forms the LCD display ) got shorted and becomes permanently in a white color state.
    Last edited by steely; 25th February 2004 at 10:27 PM.

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    And there's nothing u can do about it..

    Quote Originally Posted by steely
    It could be a hot pixel, that is a transistor ( millions of them forms the LCD display ) got shorted and becomes permanently in a white color state.

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    Quote Originally Posted by Flare
    And there's nothing u can do about it..
    Its a hot pixel. If your camera is still under warrenty, just send it in for servicing. They should be able to solve it for you.

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    Quote Originally Posted by Flare
    And there's nothing u can do about it..
    If it's a hot pixel, it should only appear on pictures shot at a slow shutter speed. Those pics you see the white dot, were they shot a shutter speed slower than 1/15sec?.

    Shoot some pics in bright daylight at higher shutter speed, 1/250 or 1/500 and see if it's still there?.

    Once I had 5 hot pixels in my cam, brought it back to the workshop and the technicians were able to re-map the CCD. They do not have to open up the camera, the re-mapping is done thru the USB terminal of the camera.

    If your camera is still under warranty, I think you should bring it to the workshop for a check-up. Don't worry if it's a hot pixel, it won't have to go on the operating table.

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    well, if its only on the lcd screen, the pictures wouldn't be affected, right?

    Hot pixel only occurs on lcd screen.. so if your pictures are fine when you download without that white spot.. mabbe can bear with it if warranty over

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    Found this on a website, it taught me more abt hot pixel, mebbe some will find it interesting as well...

    You just bought a thousand dollar digicam with full manual control and you want to show off. You take some long exposure night shots and are horrified to see a bright spot in the same part of every picture -- and it isn't a star. It's the infamous hot pixel.

    "More than a defect, hot pixels are a fact of life."

    Is your CCD defective?

    Actually, no. More than a defect, hot pixels are a fact of life. Understanding them will make you feel better, certainly, and may even suggest when you should return your digicam. So let's take an in-depth look at them.

    Your CCD is a grid of elements, each of which is sensitive to brightness.

    A hot pixel is created by an element with a higher rate of charge leakage than its neighbors which, on a long exposure, may cross the threshold of an exposed value. Many digicams don't permit exposures longer than a quarter second, which effectively eliminates the chance that any element with a dark current, so to speak, will consistently report an exposure value.

    In fact, with a long enough exposure to darkness, a disturbing pattern of exposure will appear from any CCD, because CCD elements tend to leak current. They may not all produce a bright white spot, but they are all -- with a long enough exposure -- capable of reporting exposure in darkness.

    In addition to dark current, temperature is also a factor in creating hot pixels. The higher the temperature, the higher the charge leakage. A 10 degree change in temperature can noticeably change what the CCD reports.

    Yet another factor is the ISO rating of your CCD. At ISO 400 you'll notice more hot pixels than at ISO 100, simply because the signal is amplified.

    A hot pixel can range from bright white to something just barely distinguishable from black. Or, we might say, from an artifact to noise.

    To see your camera's hot pixels, set the camera to do no image manipulation or enhancement. Use ISO 100 (if you have variable ISO settings), turn off any sharpening, contrast, or brightness settings. Assuming your indoor temperature is less than 76 F, go into a dark room, turn off the LCD monitor, cover the lens, and make exposures of 1/4, 1/2, 1, 2, and 4 seconds.

    Then take a look at these "dark frame" images. Higher magnification (say, 400 percent) makes it easier to see noise. You should expect to see a gradual increase in noise relative to the exposure length. If you find one bright pixel at every exposure setting, repeat the test with shorter exposures. You may find it does not disappear at any exposure. If that's the case, save your results to document the problem for the manufacturer and try the test again.

    Given that any CCD is going to exhibit some noise in a dark frame image, consider whether what you have is something you can live with. If you typically take long night exposures, it may not be acceptable. But remember, there's no escape. Astronomers have learned to live with the devil they know, rather than look for that elusive, perfect CCD.

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    Quote Originally Posted by Pinkishy
    well, if its only on the lcd screen, the pictures wouldn't be affected, right?

    Hot pixel only occurs on lcd screen.. so if your pictures are fine when you download without that white spot.. mabbe can bear with it if warranty over
    It could happen on your CCD as well. What you see on the LCD is a fault on the CCD, when the same is seen on your pics.

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    Hee... my ignorance... U mean they can remap the CCD, and avoid hot pixels by not using the bogus transistor on the CCD or via some other means? Man... I was told that they are part of life, as it happens and it would be commercially impratical to built CCDs with extremely small amount of hot pixels or stuck pixels (pixels that are stuck in one colour irregardless of exposure), so I'll have to live with it...

    I understand that there's a colour gride on the CCD and each transistor could actually only 'see' in one of the colour (RGB and what's the extra one on the 828?), and the final coloured pixels are actually calculated based on adjacent pixels 'seeing' in a different light (literally).

    So, just curious, what does the mapping does? disregard the stuck/hot pixels in the calculation of the pixel colour?


    And well, there's always the option of a dark frame subtraction to make hot pixels less noticable... some cameras has an automatic dark frame subtraction (I know the A1 has), and it could be done manually...

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    Quote Originally Posted by Flare
    Hee... my ignorance... U mean they can remap the CCD, and avoid hot pixels by not using the bogus transistor on the CCD or via some other means? Man... I was told that they are part of life, as it happens and it would be commercially impratical to built CCDs with extremely small amount of hot pixels or stuck pixels (pixels that are stuck in one colour irregardless of exposure), so I'll have to live with it...

    I understand that there's a colour gride on the CCD and each transistor could actually only 'see' in one of the colour (RGB and what's the extra one on the 828?), and the final coloured pixels are actually calculated based on adjacent pixels 'seeing' in a different light (literally).

    So, just curious, what does the mapping does? disregard the stuck/hot pixels in the calculation of the pixel colour?


    And well, there's always the option of a dark frame subtraction to make hot pixels less noticable... some cameras has an automatic dark frame subtraction (I know the A1 has), and it could be done manually...
    Hey you're very technical. I don't know much about these technical stuff. But I do know that if it's HOT pixel, it can be re-mapped, DEAD pixel then live with it or get the CCD changed.

    According to my unprofessional knowledge, there's one pixel for each RGB color in normal CCDs, 828 I think has an additional for purple.

    Really flare, I'm not too technical.

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    Quote Originally Posted by nokin
    Hey you're very technical. I don't know much about these technical stuff. But I do know that if it's HOT pixel, it can be re-mapped, DEAD pixel then live with it or get the CCD changed.

    According to my unprofessional knowledge, there's one pixel for each RGB color in normal CCDs, 828 I think has an additional for purple.

    Really flare, I'm not too technical.
    Hee... OooOO... Ok thanks thanks... I guess I read too much and shoot too little... =)

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    Quote Originally Posted by Flare
    Hee... OooOO... Ok thanks thanks... I guess I read too much and shoot too little... =)
    Good to read more to broaden knowledge. But photography is one thing that requires lots of practice, advice and critiques to progress and improve.

    CSers are very friendly and helpful.

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    Quote Originally Posted by Flare
    So, just curious, what does the mapping does? disregard the stuck/hot pixels in the calculation of the pixel colour?
    i think this is how its done,
    The mapping is done only to identify the location of the hotpixel
    A corrective algorithm / sub routine whatumightcallit is loaded into the camera's OS ( for those OSes that do not have this existing)

    After an image is formed
    The algo using the hotpixel map info to id the whereabouts of the hotpixels, will take a average reading of the surrounding pixels and touch up the digital image by superimposing an interpolated value into the hot pixel location.

    This can be done for the CCD, but not the LCD as LCD is the actual display element, similarly for PC LCD panels - hotpixels, you live with it.....

    cheers
    Last edited by steely; 27th February 2004 at 10:05 AM.

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