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What are the trade-offs between higher resolution pictures and camera/computer performance?

As the size of images increase with greater MegaPixel cameras, the space the image consumes in camera memory device, hard drive space and RAM increases rapidly.  Almost all digital camera color images are at least 24 bit color which allows them to choose between over 1 million colors to record for each pixel.  That means that for each pixel there are 24 bits of information.  Each byte (as in Megabyte, click here to learn about Megabytes) contains 8 bits which means there are (24/8) 3 bytes for each pixel.  That seams like a small amount, but consider my camera which has (1152x864) 995,328 pixels or (995,328x3) 2,985,984 bytes.  That means that each picture needs about 2.85Mb (Megabytes) of disk space uncompressed.  Considering that a typical 3.5" floppy disk only holds 1.44Mb, that means 1 picture would require 2 floppy disks.  In terms of floppy disks the image is quite large.  If you consider a typical 3 Megapixel camera with 1920x1600 resolution pictures, you end up with pictures that are 8.79 Mb uncompressed.  That equates to 116 pictures for every Gigabyte of disk space, or 3.24 rolls of 36 exposure 35mm film.  If you have a 20 Gb hard drive just for picture storage, you can only capture 64.7 rolls of film.  You can compress the images and most cameras do, but you sacrifice some quality, although not much if the compression is low.  My camera at the highest quality setting compresses each picture to about 0.6Mb and to about 0.2Mb at the lowest quality setting.  This allows approximately 2 pictures to be stored on a floppy at the highest quality or 6 images at the lowest quality.  A 6 Megapixel camera should end up with almost 4Mb of disk space for each image.  That's 138 rolls of film for 20Gb of hard drive space.  That's a lot of space.  I scanned an 8x10 into my computer at 600 dpi creating approximately a 28 Megapixel picture, and that picture brings my system to a grinding halt (I have a 1.4GHZ pentium 4 with 256 Mb of RAM).  Doing anything with that picture makes my computer pause for about 45 seconds before continuing (even just right-clicking on it).  That picture is equivalent to only about 4-5 six Megapixel images.

Hard disk space is not the only concern.  Most digital cameras have a rather limited storage devices in them that images can be saved on.  My camera uses the Sony Memory Stick, until recently the largest size available was 64 Mb now that has been doubled to 128 Mb.  The memory stick that came with the camera was only 4 Mb.  4 Mb is only room for about 6 images, not nearly enough to have a useable camera.

Transferring pictures from the camera or its memory device and the computer also slows down as the images become larger.  For 1 Megapixel images and larger any connection slower than USB will be unbearably slow.  USB claims transfer speeds of up to 12 Megabits per second.  The Sony USB memory stick adapter that I have claims speeds up to 3 Mbps.  Transferring 36 pictures @ 0.6Mb each (21.6Mb total) took my memory stick and USB adapter 45 seconds which is not too bad.  Transfering 36 six Megapixel images @ 4Mb each (144Mb total) should take approximately 5 minutes.  Cameras that take larger pictures or hold a lot of images should transfer by firewire.  You can see from the chart and table below that current firewire is about 30 times faster than current USB, which cuts wait times down dramatically.

After looking at all the aspects, you may want to consider the trade-offs before running out and buying a camera with a lot of pixels.

 

Technology

Theoretical Maximum Throughput
Megabits

Theoretical Maximum Throughput
Megabytes

Used For

Apple Desktop Bus

0.01 Mbps or 10 Kbps

0.0013MBps

input devices like mice, keyboards, joysticks, etc

Serial Port

0.23 Mbps or 230 Kbps

0.029MBps

printers, telephony devices, modems, etc

USB at low data transfer rate

1.5 Mbps

0.19MBps

most devices

Geoport Port

2 Mbps

0.25MBps

Geoport modem

10Base-T

10 Mbps

1.25MBPS

Laser printers, network connections, etc

USB at high transfer rates

12 Mbps

1.5MBps

most devices

SCSI

40 Mbps

5MBps

hardrives, removable storage, scanners, etc

Fast SCSI

80 Mbps

10MBps

high performance drives

100Base-T

100 Mbps

12.5MBps

Laser printers, network connections, etc

Ultra SCSI

160 Mbps

20MBps

high performance drives

Wide Ultra SCSI

320 Mbps

40MBps

high performance drives

Ultra2 SCSI

320 Mbps

40MBps

high performance drives

FireWire

400 Mbps

50MBps

hard drives, scanners, digital video

USB 2.0 (Intel)

480 Mbps

60MBps

Standard due in late 2000 or early 2001

Wide Ultra2 SCSI

640 Mbps

80MBps

high performance drives

FireWire

800 Mbps

100MBps

hard drives, scanners, digital video
Now available (3/21/00)

Ultra3 SCSI

1280 Mbps

160MBps

high performance drives

FireWire

1600 Mbps

200MBps

hard drives, scanners, digital video
(Design spec up and running 3/21/00)

 

 

How Stuff Works: decent examples of compressed images

Good Explanation of 24 bit

 


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