Q. How many pictures would
you estimate will fit in the computer? I know it depends on the HD so how many
per gig?
A.
You ask how many pictures can be stored in 1 GB of hard drive space. This is
determined by the average "size" of your pictures. The size of importance here
is not the familiar one of 8" x 10" or 4" x 6" but the computer file size like
50 KB or 400 KB or 2 MB. You can judge for yourself what your typical picture
file size is on your computer by examining files sizes using Windows Explorer. I
have many thousands of photos that are in the range of 350 to 500 KB. These are
JPEG files holding pictures from a 2 MP camera. I also have a lot of files in
the 600 to 650 KB range from my 3 MP camera.
So, the short answer to your question for my typical photos would be:
About 2000 or 2500 pictures per GB for my 2 MP pictures and
About 1600 pictures from my 3 MP camera.
With a 80 GB hard drive you could store some 80,000 2 MP pictures and still use
up only half of your drive -- that's a lot of pictures!
How do I arrive at these numbers?
There are several things that determine how "big" picture files are on your
disk:
1. Resolution (i.e., pixel dimensions) - how many pixels are in the image (e.g.,
1600 x 1200 or 720 x 480)
2. Bit Depth (or color depth) - how many bits or bytes it takes to record each
pixel of the picture.
3. Format (and options) that the file is written in
You get the actual number of pixels in the image by multiplying the width (e.g.,
1600) by its height (e.g., 1200) to get its total number of pixels (e.g., 1600 x
1200 = 1,920,000 pixels -- typical for a 2 megapixel camera).
Each pixel is simply a single code number that identifies the color or shade for
that particular point on the image. The "bit depth" of the image determines the
amount of computer space that is needed for this code number of each pixel. The
most common bit depths that you will encounter are 8 (for the 256 possible
shades of gray in a gray scale ("black and white) photo and 24 bits for the "16
million" possible colors in a color photo. Remembering that a byte is 8 bits
then we can see that a gray scale picture requires 1 byte per pixel while a
color photo requires 3 bytes per pixel. So our typical 2 megapixel photo
mentioned above will require 1920000 pixels x 3 bytes each = 5,760,000 bytes of
memory.
The actual size of the picture file depends upon the format used to write the
picture -- the file may be larger or smaller than the size calculated above
because the file may contain other data besides the image pixels and the format
may be able to compress the gross number of pixels to a smaller number by doing
some smart math on the image pixels. When the image file is opened to view or
edit the picture then the compression must be undone to restore it to the
original gross pixels.
Examples of other data that may be stored in the file in addition to the image
pixels are: date picture was taken, date picture was last edited, exposure
settings, focal length of the lens, photographer's name, etc. This is commonly
called EXIF data.
Some formats may store a very large amount of additional data, for example the
PSP format may store multiple layers, alpha channels, etc. that could increase
the amount of data stored by several fold.
Many common formats apply compression to reduce the size of the file. BMP, GIF,
TIFF and JPG files all are capable of varying amounts of compression. BMP, GIF
and TIF formats may only reduce the file size by 10%, 20% or a bit more, whereas
JPEG may reduce the size by 90% or 95%! There is a major difference between
types of compression though -- BMP, GIF & TIFF use lossless compression to do
their relative anemic reduction while JPEG uses a lossy compression to do its
much greater magic. What this means in practical terms is that the restoration
to original size is perfect for the lossless formats but not for JPEG -- there
is some loss of detail or introduction of noise in the lossy restoration. So
there is a tradeoff between file size and quality.
Alex