Expert: Candice Anderson - 5/15/2006

Question
My daughter insists that, when she opens a JPEG file from her Canon EOS350D (an 8 million megapixel digital camera), Photoshop opens it at around 22 megabytes.  This is the figure (approx) that appears on the bottom left-hand corner of the screen - as 22M.

I appreciate that opening a JPEG file in Photoshop uncompresses it but I do not believe that the file could be this large.  I say that the 22M refers to megapixels, not megabytes.

Please advise what this figure at bottom left of screen refers to: megapixels or megabytes?  

Also, is there a direct relationship between megapixels and megabytes?  For example, if the image size of a file (in Photoshop)is shown as 2272 x 1704 megapixels (at 72 pixels / inch) and the pixel dimensions are shown as 11.1M (this figure is also shown at bottom left of the screen), can you calculate the file size?

I would appreciate your advice!  

Philip  

Answer
hey Phillip,

sorry, your daughter is right.  That file is very much 22 megabytes.  Put it to you this way, I have a 4 megapixel camera and mine open up to 11 megabytes. Her camera is able to make very large photos :)

there is a relationship between pixels and bytes.  I don't know the exact calculation, but there is one.  Megabytes, or bytes, are how big the file will be.  Pixels or Megapixels are how many dots are in each picture.  So her very awesome camera is able to take a picture containing 8 million pixels and is able to print that at around 8.5 by 11 inches without making it bigger.  My little camera has 4 million bytes and therefore will print out smaller.

bascially, the more pixels, the more information, the bigger the file size.

and the bottom left number is bytes or megabytes.

Also, my apoligies if you already know this, since you have photoshop, create a new file and make sure your dpi is at 300.  72 dpi, or dots per image is very low for print.  When you move the picture over to the 300 dpi document (litterally take the image from one block and move it over :) )  you will notice that it will shrink. this is because 300 dpi is more, but is the approiate amount for printing. It will not only shrink your photo to 8.5 by 11, but the make your file quite large in bytes.

hope this helps :)

Candice