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Old Sep 19, 2004, 3:41 PM   #1
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Can someone explain why my C-750 photos get extremely grainy after the camera has been on for 20 or 30 minuites. I was taking pictures of a flag football game that lasted 2 hours and when I downloaded my pictures the first 20 minuites of photos were great but after that they slowly got so grainy that they were unuseable. Anybody have an idea?
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Old Sep 19, 2004, 6:40 PM   #2
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Without seeing your photos (and looking at the camera settings), it would be hard to say for sure.

Was the light changing (slowly getting a little darker out after the first 20 minutes or so)?

If so, then the camera may have been boosting ISO speed to try and keep shutter speeds faster. This increases the sensitivity of the CCD Sensor to light (but it also increases noise -- which is the grain you're seeing).

The other possibility is that the CCD was getting hot (heat can also increase noise). This cause is very unlikely. Chances are, it was just the ISO speed.

The camera settings used for your photos are in the EXIF (a header in the image files). If you don't have an image editor than can see this information, download irfanview from http://www.irfanview.com (it's free). Make sure to download the plugin's, too.

When you open an image, the camera settings will be under Image, Information, EXIF.

Rather than using Auto ISO (which will automatically increase it up to a point as needed), you can also set the ISO speed to a fixed value with your model (50, 100, 200, or 400). Each time you double the ISO speed, the camera can use shutter speeds twice as fast for the same lighting conditions and aperture.

The upside of increasing ISO speed is that you will have less motion blur. The downside of increasing ISO speed is higher noise levels.

So, in some lighting conditions (unless you want blurry photos), you may have no choice to increase ISO speed. If your football game was in the evening, then you will need to increase ISO speed to have any chance of getting photos without motion blur (the light in a well lit stadium is actually pretty dim compared to daylight, even though it looks bright to the human eye).

There are some good tools to reduce the appearance of noise. Here are a few:

http://www.neatimage.com

http://www.picturecode.com

http://www.imagenomic.com (this one has a free version)
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Old Sep 19, 2004, 8:40 PM   #3
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My ISO was set at 100 and it was a clear sunny day at about noon. I would send the pictures but it keeps telling me the file size is to big and gives me an error message. I down sized them to 640x480 but it still said they were to big. This is the first time I have left my camera on for a long period of time without cutting it off or letting it go into sleep mode. Do all digital cameras suffer from hot CCDs and cause grain in fotos?
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Old Sep 19, 2004, 8:54 PM   #4
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arowana wrote:
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My ISO was set at 100 and it was a clear sunny day at about noon. I would send the pictures but it keeps telling me the file size is to big and gives me an error message. I down sized them to 640x480 but it still said they were to big. This is the first time I have left my camera on for a long period of time without cutting it off or letting it go into sleep mode. Do all digital cameras suffer from hot CCDs and cause grain in fotos?
No. That's why I said that it would be very unlikely. Usually, heat impacts longer exposure photos (which is not what you're doing).

E-mail me one and let me take a look to see what you're talking about. I'll send you my e-mail address via a PM.

Added:

I sent you my e-mail address. Also, let me know if you want me to post a copy to the forum here.





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Old Sep 19, 2004, 10:22 PM   #5
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Here are the settings for your two images from the EXIF (minus the "data dump" section). As discussed via e-mail, the grain you are seeing is actually being caused by noise (due to an ISO speed of 200 used by the camera).

My guess is that the mode you were in ignored your ISO speed settings. With some models, ISO speed settings are only honored in certain modes.

The date/time information has been stripped from the EXIF (probably when you downsized the images for e-mailing).

flag football 2.jpg

ImageDescription - OLYMPUS DIGITAL CAMERA
Make - OLYMPUS OPTICAL CO.,LTD
Model - C750UZ
Orientation - Top left
XResolution - 72
YResolution - 72
ResolutionUnit - Inch
Software - v753u-79
DateTime - 0000:00:00 00:00:00
YCbCrPositioning - Co-Sited
ExifOffset - 550
ExposureTime - 1/250 seconds
FNumber - 3.20
ExposureProgram - Creative program
ISOSpeedRatings - 200
ExifVersion - 0220
DateTimeOriginal - 0000:00:00 00:00:00
DateTimeDigitized - 0000:00:00 00:00:00
ComponentsConfiguration - YCbCr
CompressedBitsPerPixel - 2 (bits/pixel)
ExposureBiasValue - 0.00
MaxApertureValue - F 3.25
MeteringMode - Multi-segment
LightSource - Auto
Flash - Not fired, compulsory flash mode
FocalLength - 34.70 mm
UserComment -
FlashPixVersion - 0100
ColorSpace - sRGB
ExifImageWidth - 640
ExifImageHeight - 479
InteroperabilityOffset - 1268
FileSource - DSC - Digital still camera
SceneType - A directly photographed image
CustomRendered - Normal process
ExposureMode - Auto
WhiteBalance - Auto
DigitalZoomRatio - 0.00 x
SceneCaptureType - Standard
GainControl - Low gain up
Contrast - Normal
Saturation - Normal
Sharpness - Normal

Maker Note (Vendor): -
SpecialMode - 1504
JpegQual - 1
Macro - 0
Unknown - 0
DigiZoom - 1.00
Unknown - 7.16
Unknown - 1532
Software Release - SX753
PictInfo - [pictureInfo] Resolution=1 [Camera Info] Type=SX753
CameraID - OLYMPUS DIGITAL CAMERA


flag football 3.jpg

ImageDescription - OLYMPUS DIGITAL CAMERA
Make - OLYMPUS OPTICAL CO.,LTD
Model - C750UZ
Orientation - Top left
XResolution - 72
YResolution - 72
ResolutionUnit - Inch
Software - v753u-79
DateTime - 0000:00:00 00:00:00
YCbCrPositioning - Co-Sited
ExifOffset - 550
ExposureTime - 1/200 seconds
FNumber - 3.70
ExposureProgram - Creative program
ISOSpeedRatings - 200
ExifVersion - 0220
DateTimeOriginal - 0000:00:00 00:00:00
DateTimeDigitized - 0000:00:00 00:00:00
ComponentsConfiguration - YCbCr
CompressedBitsPerPixel - 2 (bits/pixel)
ExposureBiasValue - 0.00
MaxApertureValue - F 3.73
MeteringMode - Multi-segment
LightSource - Auto
Flash - Not fired, compulsory flash mode
FocalLength - 63.00 mm
UserComment -
FlashPixVersion - 0100
ColorSpace - sRGB
ExifImageWidth - 640
ExifImageHeight - 479
InteroperabilityOffset - 1268
FileSource - DSC - Digital still camera
SceneType - A directly photographed image
CustomRendered - Normal process
ExposureMode - Auto
WhiteBalance - Auto
DigitalZoomRatio - 0.00 x
SceneCaptureType - Standard
GainControl - Low gain up
Contrast - Normal
Saturation - Normal
Sharpness - Normal

Maker Note (Vendor): -
SpecialMode - 1504
JpegQual - 1
Macro - 0
Unknown - 0
DigiZoom - 1.00
Unknown - 7.16
Unknown - 1532
Software Release - SX753
PictInfo - [pictureInfo] Resolution=1 [Camera Info] Type=SX753
CameraID - OLYMPUS DIGITAL CAMERA

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