card capacity

This is no big deal but I'd really appreciate it if someone could explain to me this apparent anomaly:

1gb Sandisk card in *istDS shows a JPEG capacity of 334 images at 6mp
Same card in S50 shows a capacity of 309 images at 5mp.

Does anyone know why?

Ken

Hi Ken,

can't help.. sorry. I just had a look at the specs of each, and the only thing I can come up with is that the S50 uses 12 bit jpeg, and the DS uses 2.21 exif. I was looking to see if the S50 used 16 bit and the DS 12 bit, which may have explained it, but that didn't work.

I think this is one for Matt, or one the other techies here.

Cheers

Liam

JPGs are funny old things

You have to remember that the size of a JPG file is more related to visual frequency than pixel count. The more high frequency information, the larger the JPG. Added to that is the "quality" of the JPG save - a higher quality will retain more of that high frequency information.

My guess is this:
1. The CCD on the *ist-DS is much cleaner. All compact digicams produce a ton of noise in comparison. Image noise = high frequency which bloats the size of the JPG

2. It is likely that the S50 will tend to oversharpen in comparison to the *ist-DS, and again this increases the high frequency components

3. The image count is only a guide. Actual number of shots depends on the nature of the image

4. Not sure if there's a way to work out what quality setting was used for the JPG creation. The S50 and *ist-DS have completely different operating firmware, and you can't quite tell what setting they're using. The choices available in the camera settings are usually quite "coarse", but the JPG algorithms allow a very fine degree of tuning (like when you save under Photoshop).

There are lots of articles on the web about JPG that I could dig up to explain it all. Let me know if you need any
Matt

Thanks to both of you.

I'm quite happy to live without worrying about the intricacies of this!

Ken