When taking photos with a digital camera it is useful to know how many photos will fit on your memory card (SD, Memory Stick Duo, USB, etc), and know how large the JPEG images are.
There are a lot of tables out there showing this kind of information. I don’t trust other people’s numbers so I decided to calculate them myself and produce some charts to show how the number of megapixels you use when taking the photo affects how many photos will fit on the card.
| MP | 0.3 | 1 | 2 | 3 | 4 | 5 | 7 | 10 | 12 | 15 |
| 256MB | 1896 | 569 | 284 | 190 | 142 | 114 | 81 | 57 | 47 | 38 |
| 512MB | 3793 | 1138 | 569 | 379 | 284 | 228 | 163 | 114 | 95 | 76 |
| 1GB | 7585 | 2276 | 1138 | 759 | 569 | 455 | 325 | 228 | 190 | 152 |
| 2GB | 15170 | 4551 | 2276 | 1517 | 1138 | 910 | 650 | 455 | 379 | 303 |
| 4GB | 30341 | 9102 | 4551 | 3034 | 2276 | 1820 | 1300 | 910 | 759 | 607 |
| 8GB | 60681 | 18204 | 9102 | 6068 | 4551 | 3641 | 2601 | 1820 | 1517 | 1214 |
The table above is what I came up with. I made the assumption that the images are stored as JPEGs and the compression ratio is 15:1. That is a rough average of what my Sony Cyber-shot W80 camera is compressing my photos at.
The compression ratio can have a big effect on the size of your photos. It can for example make the difference between your photo being 2MB in size or being 4MB in size.
This graph shows the JPEG photo size when using low compression (which I’m defining as 10:1) and high compression (which I’m defining as 20:1).
My second graph shows how many photos you can fit on a 4GB card. I chose 4GB as this is quite a typical memory card size for today’s digital cameras. You can see that a small decrease in the megapixel resolution (that you shoot the image at) can allow you to fit a lot more photos on the card.
Here’s a table of the average JPEG image sizes for differing megapixel resolutions.
| MP | 0.3 | 1 | 2 | 3 | 4 | 5 | 7 | 10 | 12 | 15 |
| Size (MB) | 0.14 | 0.45 | 0.9 | 1.35 | 1.8 | 2.25 | 3.15 | 4.5 | 5.4 | 6.75 |
If you take a lot of photos then I’d recommend you try decreasing the number of megapixels in your photos. Most digital cameras will allow you to do this very easily. Today 10MP and 12MP cameras are common, but this level of detail is way more than most people need. Megapixels are a marketing game played by camera manufacturers.
By having the resolution too high you are just decreasing the amount of pictures you can take, increasing the space they use on your computer, and increasing the time it takes to process or upload them.
I have a 7MP camera. I have turned it down to 5MP because I find 5MP to be sufficient. You get great photos at 5MP – they look great on screen and great when they are printed out on 6×4 inch or 7×5 inch photo paper.
Give it a go, and see if you notice any difference.
