Different card capacity depending on ISO setting?

[colintinto]

Hi Guys,

Discovered something slightly strange at the weekend. With my 300D, and an empty 1Gb memory card, in RAW mode, it estimates it has space for 140 pictures at ISO 100, but only 119 at ISO 1600.

I think I have an explanation - 'noisy' pictures don't compress as easily as clean pictures, as there is effectively more detail, even if it's unwanted detail.

I've noticed that with video - recording an anaog TV programme that's slightly fuzzy takes up more space than one with a nice clean signal.

Does that sound plausable? I didn't think they'd take that into account when calculating how many images would fit...

As an aside, took quite a few pics at ISO 1600 at the weekend, and I was impressed at how little noise there was!

Colin

 

[hobbes28]

That would sound plausable but the RAW image is uncompressed. The estimation for how many shots you can take are just that, an estimation. The size of a picture depends on the colors, detail, lighting..etc. When you take the picture at ISO 1600, you're already adding in the details that will be picked up by having a speed that's that much faster so it's making an estimation based on the potential to pick up more information.

Hope this helped.

 

[Big Mike]

I've also heard that the actual image can affect file size. For example, a very busy scene with many color/shades etc. will be bigger than a shot of blue sky.

 

[Marctwo]

That would sound plausable but the RAW image is uncompressed.

I don't know of any raw formats that are not compressed - they just use a less efficient lossless algorithm.

If they weren't compressed, you'd only get about 40-50 shots on a 1GB card.

 

[Meysha]

I've also heard that the actual image can affect file size. For example, a very busy scene with many color/shades etc. will be bigger than a shot of blue sky.

True! This happened to me yesterday. I was taking photos of chocolates but because I can only use my flash in manual mode it takes me a couple of shots to get the flash at the right strength. So a couple of pics were completely blown out - just white, they were a lot lot lot smaller than the well exposed, lots of detail and colour pictures.

Which makes sense, because there's less data therefore smaller file size.

 

[NeoDude]

If they weren't compressed, you'd only get about 40-50 shots on a 1GB card.

I disagree. You would be able to fit about 160 uncompressed 6 Megapixel images on a 1GB card.

 

[tr0gd0o0r]

I disagree. You would be able to fit about 160 uncompressed 6 Megapixel images on a 1GB card.[/quote

Dang it, i knew my camera was adding stuff to my photos..... i only get about 70

 

[Marctwo]

I disagree. You would be able to fit about 160 uncompressed 6 Megapixel images on a 1GB card.

How do you work that out?

At 36bit each pixel is 4.5 bytes if stored efficiently, so 6MP = 27MB at the very least.

 

[Meysha]

I disagree. You would be able to fit about 160 uncompressed 6 Megapixel images on a 1GB card.

Hmmm... That sounds like too many to me. Are you sure they're not compressed jpegs? Or are you sure you're shooting at the full 6MP?

 

[NeoDude]

Ignore me. I was being stoopid. I was taking a 6mp RAW file to equal 6MB.