Megapixel Confusion

[Mort]

I have an 8 megapixel camera and shoot my photos at this resolution. When I check the size of my photos in Elements 4.0, I find they are on the order of 22 megapixels. How can I have more megapixels than the what the camera produces?

[Carbone]

What you're seeing in PSE is the size the image is taking in memory in megabytes, not the number of pixels in megapixels. Two different measures, but easily confused!

Ray

[Mort]

Thanks, Ray. It would be less confusing if Adobe called it megabyte dimensions instead of pixel dimensions. But, I am under the impression that an 8 MP file contains less than 8 MB so I still don't see the relationship between a file that is 2,448 x 3264 pixels (7.99 MP) and 22.9 MB. It is still confusing.

[Chuck S.]

Mort, an 8 megapixel image will indeed be around 23 megabytes in its uncompressed state because it takes approximately 3 bytes to characterize each pixel. 8 megapixel images are only smaller when they're compressed, which is what happens in your camera and again if you save the photo to JPEG. Yep....it's confusing....

Chuck

[Mort]

Thanks Chuck. I think you are saying that there is an R,G, & B for each pixel. That would give me about 22 MP and Elements 4.0 is stating this as the pixel dimensions. We don't yet need to get into the discussion of MB since the Resize window only addresses MPs and not MBs.

[Chuck S.]

Mort, you're close: a pixel is made up of R,G,and B channels and requires one byte for each channel. Therefore, one pixel is 3 bytes, 1 megapixel is 3 megabytes. etc. At least according to Photo.Net:

The size of the digital file corresponding to the image which the camera produces depends on the pixel count. In most consumer digicams each pixel generates 3 bytes of data (so called "8-bit data"). One for red, one for green and one for blue. This means that a 3MP camera, which has 3 million pixels, generates 9 million bytes of data, or 9MB (megabytes).

More info at:

http://www.photo.net/equipment/digital/cameras/basics/

Chuck

[virgo1]

Chuck,
Thank you very much for the link. I found it helpful. :)
Eva ;)

[Carbone]

Chuck, you're very good with numbers... Image resolution, Picture dimension, Megapixels...

Chuck, our PSE arithmetic resident teacher :)

Ray

[Chuck S.]

Ray, thanks. I guess everyone needs their niche...

:rolleyes:

[Mort]

So Chuck, following your logic (and your much appreciated reference) and the information presented in the Resize window of Elements 4, my 8 MP camera generates image sizes of ~23 megapixels which just happens to also be equal to 23 megabytes. However, this implies that one megapixel is equal to one megabyte, or that a pixel equals a byte, and we know that is not true. So, I'm not perfectly clear even though I do understand your explanation. It is no wonder that people get confused about these numbers. Any further clarification would be appreciated.

[Chuck S.]

Mort, your camera generates an image that has 8 megapixels; it takes 3 bytes of data to characterize a pixel. 8 megapixels need around 24 megabytes of data storage (uncompressed). Best thing to remember as a rule of thumb: 1 pixel = 3 bytes.

Chuck