File size

[dave92029]

I have a Canon 30D and I shot in large jpeg. If the sensor has "only" 8.2 mp

how come my files are over 10mp? Here is the shooting information from Canon

ZoomBrowser EX:

 

File Name IMG_0440.JPG

Camera Model Canon EOS 30D

Shooting Date/Time 7/21/2006 11:08:08 AM

Tv( Shutter Speed ) 1/200

Av( Aperture Value ) 10

ISO Speed 320

Image Size 3504x2336

Flash Off

Parameters Settings

File Size 10678 KB

 

The scene is of the court yard of Mission San Juan Capistrano. I used a 24-

105MM f4L IS lens.

 

Thanks in advance

[ekoppel]

The sensor is 8.2 megapixels. If you take the width of the image and multiply it by the height of the image, e.g. 3504 * 2336, you get approximately 8,200,000 which is 8.2 megapixels (mega is a million).

 

If the image is in full color, each pixel consumes 24 bits (8 bits for Red, 8 bits for Green, 8 bits for Blue). So take 24 bits and multiply it by 8,200,000 and you get 196,800,000 bits which converts to 24,600,000 bytes, or 24.6 megabytes.

 

But since you saved the file as a JPEG, the image gets compressed and there is quite a bit of data loss but not so much that it is truely visible by your own eyes.

[PuppyDigs]

JPEG size is subject to the amount of compression you apply, ISO and subject matter. If

you

reduce it from JPEG Large Fine to JPEG Large Medium you'll apply more compression and

thereby reduce file size. If you shot at ISO 100 rather than 320 the file will be even

smaller.

Finally, if you limit yourself to monohues or even textures--blue sky or white wall shots--

your files will shrink even more (complicated scenes don't compress well--less info can be

tossed).

 

Personally I wouldn't waste all that ultra fine optical and MP qualiy on compressed JPEGS.

The RAW

output is so much better...

[wolver]

Eric, that is the best to the point explanation of file size I have ever read on the net. Kudos to you!

[dave92029]

Thank you very much. Your explaination makes a lot of sense. I've tried raw but had problems up loading the files to Smugmug (where I post most of my work) even after converting the raw files to jpeg after working on them. I have a lot more experience now and probably should try using raw files again.

Again thanks for the excellent comments.

[KenPapai]

An 8MP (note ALL CAPS) original image file rendered as a JPG will be anywhere from 1MB to 10MB in size (again, note the ALL CAPS and the 'B' rather than your 'p').

 

Three main variables determine the JPG file size: the amount of compression you choose, how many different colors, and how sharp or variegated the original image is.

[JeffOwen]

As a general rule of thumb I multiply the camera pixel size by three (three colours) to get the uncompressed file size. The final jpg size will vary from 1/4 down to 1/80 of that size. i.e. one of my tiff files from my 8.2M pixel camera is 23.6Mb uncompressed, when I use jpg (best, least compressed) it is 5.64Mb and jpg (most compressed) it is 0.30Mb.