Question about image size

[glamourbyjim]

Hope that someone who is more technical can explain this to me.

Just replaced my D60 with the 20D. Love everything about the camera.

Here is the question: The manual states that the camera will produce a 8+ meg jpeg image at Large Fine Jpeg setting. Medium Fine jpeg of about 4 meg.

After shooting a bunch at the largest fine, and placing them on my PC with Breeze Downloader - on disk they are various sizes, but all about 2 meg each.

Where are the 8 meg images?

Thanks

Jim Malachowski
www.glamourbyjim.com

[Belmondo]

They're there-----compressed using JPEG.

If you want the full 8MP experience, shoot raw.

[Jon]

That's 8 Megapixels. You're seeing the file size in megabytes. File size of Jpegs will vary depending on the complexity of the image. A photo of a blank wall wil lbe very small, while a photo of a flower garden in full bloom will be pretty large. But when you open them in an image editor or viewer, they'll still show the 20D's 3504 x 2336 pixel image size.

[Jim_T]

Yes. You're assuming a pixel and a byte are the same thing because they both start with mega..

Mega simply means 1 imillion.. A million watts of power is a megawatt and despite starting with the prefix 'mega' it has nothing to do with bytes or pixels :)

The camea has a sensor that can produce 8 million samples of the light falling on it. The samples are arranged in a grid. Each 'sample' is a pixel which is short for 'picture element' --- picture = pix, element = el. ........ pixel

These samples are digitized and represented as bytes.. But it takes MORE than one byte to represent the information held in one image sample... Each sample contains a color hue and a brighntess value.

In order to store the informaiton in one pixel using 8 bit format (like JPEG does), you need 3 bytes.. An 8 bit image will then be 3 x 8 Million = 24 million bytes, or 24 megabytes. (This is what you'll see if you save a RAW file in 8 bit TIFF format.). If you save it in 16 bit format, it will be 48 Megabytes.

Your JPEG images aren't 24 megabytes in size because they use compression. They are shrunk down to 2 - 3 megabyes and stored that way. This saves a LOT of memory card space..

When you select 'fine' and 'superfine' in the JPEG menu, you are selecting the amount of JPEG compression that is used. Fine images will be smaller than superfine images because fine uses more compression.. But this doesn't come for free.. JPEG compression is lossy and you lose a bit of image quality when you use superfine, and even more quality when you use fine.

Your RAW files are 12 bit, They should be 32 megabytes, but they're compressed too so they come out much smaller. You can't select the compression rate for RAW.. The RAW compression isn't lossy and doesn't effect the quality of the image the way JPEG does.

[glamourbyjim]

Thank you all for the answers.

Jim