Digital Camera Card Capacities...

[David_Loves_Ubonwan]

I have two digital cameras, both 12MP Nikons and find that the 'remaining photos' available to be stored on my SD cards is wildly under-estimated.

Both cameras on highest quality produce a filesize of around 4.7MB. Putting a formated 128MB card in either of them I'm told I can take 15 photos but dividing 128MB by 4.7MB gives 27 photos???

Similarly putting in a 8GB card my dSLR tells me I can take 1.1k (1,100) photos whereas 8GB divided by 4.7MB tells me I can take 1,730+ photos. I think my compact just says 'more than 999'.

Is this common in all brands of camera? And why when it is such an easy calculation?

David

[Khun Don]

Some of the space must be used for the information that is recorded about each image etc

http://www.tomshardware.co.uk/forum/...t-space-reduce

Explains it better than I can

[aardvark]

It's a complex calculation and one that depends on sector sizes etc.

Lets say you have a 500Mb Card and each sector is 1Mb. Therefore you can store 500 x 1Mb files. However if each file is 1.1Mb then in fact you need 2x1Mb sectors to store each file and the number of files you can now store is only 250 as each file now takes 2Mb despite the actual size being 1.1Mb

This explains how 256x1.1Mb = 281mb will fill a 500mb card.

I know I have simplified it a bit but the above is sort of how it works. In reality the wastage is much lower than this, although the opposite of storing very small files will fill a hard disk quite quickly (unusual scenario though)

Hope this explains it.

[paul_au]

David like every thing, we get ripped off, don't matter what we buy in terms of capacity, it is always less than the generalization specified. I notice this with cars. when ever a car states a 2 litre engine in it's specifications, you can look up the exact specifications and it is something like 1.9654 litres, in all my years I have never seen a car with more than the litres generally specified in the hand book.

[David_Loves_Ubonwan]

It's a complex calculation and one that depends on sector sizes etc.

Lets say you have a 500Mb Card and each sector is 1Mb. Therefore you can store 500 x 1Mb files. However if each file is 1.1Mb then in fact you need 2x1Mb sectors to store each file and the number of files you can now store is only 250 as each file now takes 2Mb despite the actual size being 1.1Mb

This explains how 256x1.1Mb = 281mb will fill a 500mb card.

I know I have simplified it a bit but the above is sort of how it works. In reality the wastage is much lower than this, although the opposite of storing very small files will fill a hard disk quite quickly (unusual scenario though)

Hope this explains it.

Having worked with computers for the last quarter century or so I am aware of the 'overheads'; FAT etc. But I thought the estimatation given by the cameras was so wildly out that it warranted comment.

I did an experiment with a 128MB card. Camera suggested it would hold 15 images, calculation suggested 27 images and in practise it filled up after 23 images. So it held more than 50% more than the cameras suggest and only 15% less than my calculation...

David

[GkapiBreath]

With JPEGs, subject matters: a photo of bushy foliage does not compress as well as a photo of a large area of mostly flat color. I think those "remaining image" counts are based on a worst-case scenario rather than a true average.