Go Back   Steve's Digicams Forums > Digital SLR and Interchangeable Lens Cameras > Pentax / Samsung dSLR, K Mount Mirrorless

Reply
 
Thread Tools Search this Thread
Old Aug 30, 2011, 12:52 AM   #1
Senior Member
 
Join Date: Aug 2010
Posts: 120
Default Pentax K-X File Size

I thought that if you have a 5MB camera, the jpeg file size would be 5MB. So, with the K-X, should it be 12.4MB? My files are only 5 to 6MB each. I already set to the best quality.
raylee011 is offline   Reply With Quote
Sponsored Links
Old Aug 30, 2011, 6:04 AM   #2
Senior Member
 
Join Date: Apr 2010
Posts: 584
Default

Quote:
Originally Posted by raylee011 View Post
I thought that if you have a 5MB camera, the jpeg file size would be 5MB. So, with the K-X, should it be 12.4MB? My files are only 5 to 6MB each. I already set to the best quality.
Don't confuse bytes with pixels.

An uncompressed image file will be the number of pixels stored
times the number of bytes stored for each pixel. This never works
out in practice because most cameras use some form of compression.

JPEG files use lossy compression which gives a substantial reduction
in file size. Some RAW formats use non-lossy compression which
gives some file size reduction without any loss of image quality.

Most if not all cameras will produce files which are smaller than
the size of the uncompressed RAW image. Your K-x captures
12.4MP at 12 bits (1.5 bytes) per pixel. You could expect RAW
images to be over 18MB. The actual K-x RAW files are about 12.5MB
and JPEGs are around 5MB (depending on image).

Last edited by corkpix; Sep 1, 2011 at 3:21 AM.
corkpix is offline   Reply With Quote
Old Aug 30, 2011, 9:31 AM   #3
Senior Member
 
Zuken's Avatar
 
Join Date: May 2009
Location: Cincinnati
Posts: 175
Default

Quote:
Originally Posted by corkpix View Post
Don't confuse bytes with pixels.

Most if not all cameras will produce files which are smaller than
the size of the uncompressed RAW image. Your K-x captures
12.4MP at 12 bits (1.5 bytes) per pixel. You could expect RAW
images to be over 18MB. The actual K-x RAW files are about 12.5MB
and JPEGs are around 5MB (depending on image).

Excellent explanation. Simple and easy.
__________________
Armando
PentaxK-x
Kit lens 18-55mm
Sigma 70-300mm f/4-5.6 DG Macro Autofocus
http://razzi.me/zuken
Zuken is offline   Reply With Quote
Old Aug 30, 2011, 10:01 PM   #4
Senior Member
 
mtngal's Avatar
 
Join Date: Nov 2005
Location: Frazier Park, CA
Posts: 16,052
Default

To add a bit more to the file size/pixel differences (corkpix's "depending on image" qualification) - if your pictures are raw files or full sized jpg files, they will always have the same number of pixels across and down (multiply the two numbers and you'll get the total number of pixels the camera is capable of). However you can have two pictures that have the same number of pixels but different sized files. A picture of a featureless sky will have a smaller file size than a picture of some complicated, busy pattern like the bark of a gum tree or a sugar pine. I'm a knitter so I imagine the file size working like a knitting pattern. The simpler the pattern, the shorter the directions and the chart. A more complicated one is longer and has a bigger chart. In the same way, a file of a picture filled with a solid color (like a featureless sky) will be smaller than a picture filled with the bark of a gum tree or sugar pine (both have complicated bark patterns).
mtngal is offline   Reply With Quote
Old Aug 31, 2011, 5:13 PM   #5
Senior Member
 
Join Date: Jan 2011
Location: Australia, New South Wales central coast
Posts: 2,891
Default

G'day raylee

You have discovered "our old friend JPEG"
As mentioned above, JPEG is a method of compressing the ex-camera image via some very smart maths so that the pixels that reach the memory card are reduced in quantity thus making saving quicker & reducing space-used on the memory card.

The JPEG maths also puts copies of those pixels back again during printing, so that you end up with the same megapixel count as you started with, although some / many of the pixels are copies ~ that's another story - see below

Your camera will offer you several menu choices of "image quality" relating to JPG images ~ they may be called "Fine or Normal or Basic" or "Best or Normal or Email" or "3-stars or 2-stars or 1-stars" ... whatever it is, the JPEG math formula removes pixels on the way to the memory card but don't worry too much as it puts 'em back for viewing or printing

eg-like this sketch shows


The "However" side of things is that if you compress the image too much [ie- delete too many pixels during saving] then you don't have enough pixels to view/print later on, thus the image will look "chunky" when viewed/printed

Regards, Phil
__________________
Has Fuji & Lumix superzoom cameras and loves their amazing capabilities
Spends 8-9 months each year travelling Australia
Recent images at http://www.flickr.com/photos/ozzie_traveller/sets/
Ozzie_Traveller is offline   Reply With Quote
 
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -5. The time now is 4:11 PM.