ISO and file size

[Markk9]

Does a lower ISO make for a smaller or larger file? If i took 2 photos of the same object one at ISO 100 and the other at ISO 1600 which would have the smaller file size? Or is there not that much difference to worry about?

Mark

[Kolor-Pikker]

Raw data uses compression where noise, detail and exposure increase file size. a Raw from my 5D2 can range from less than 22mb for a dark ISO100 shot handheld, to over 33mb for a bright ISO3200 shot on a tripod.

Jpeg depends on details as it preserves edges and smooths flat areas - so detail, noise and sharpening account for file size.
A full-size jpeg out of my 5D2 can be 6-7mb in size for a typical photo, or 20mb if I fill the frame with an lcd monitor, and then sharpen it to boot.

Tiff can use lossless compression, so most tiffs tend to be about the same size if the resolution is the same, I get 55~60mb for an 8-bit tiff and up to 120mb for a 16-bit tiff from a 5616x3744 file.

Png just saves the pixels as-is and is lossless, as such it takes up the most space.

[Brikwall]

The ISO 100 file would be smaller.

The higher the ISO, the more noise. Noise adds detail. Detail increases file size.

A simple example is to set your ISO to 100 and then insert a freshly formatted memory card into your camera. The LCD counter will show how many images can fit onto the card. Note that number. Now, set your ISO to 1600 and note that same number. It should be lower.

[egordon99]

I believe it's more a case of noise being random, and random data doesn't (losslessly) compress as well as non-random data...


(I have a degree in Computer Science and minored in Mathematics, but forgot most of what I learned in undergrad :lol: )

[John Sheehy]

Does a lower ISO make for a smaller or larger file? If i took 2 photos of the same object one at ISO 100 and the other at ISO 1600 which would have the smaller file size? Or is there not that much difference to worry about?


If they both have the same relative exposure (histogram, or JPEG brighness), then they are the same except that the higher ISO has more random pixel values, and is less compressible in the lossless RAW. Note that these RAWs are not as compressed as they can be; they are probably optimized for compression and decompression time; not for maximum lossless compression. I've made uncompressed DNGs from CR2s and loaded them into for 7Zip and compressed them maximally, and they were about 1/3 the size of the CR2s and compressed DNGs.

Another thing to note is that a low ISO pushed to 1600 compresses better than a real 1600 (as long as the extra highlights are only sparsely used). There is a noise penalty for doing this on Canon DSLRs and some recent Nikons, but if you're above 1600, there is little or no noise penalty for underexposing as opposed to using a higher ISO, and for some cameras like P&S cameras with RAW, you get a tad less noise and much smaller files by shooting *everything* at base ISO, at various levels of under-exposure, with smaller RAWs.

[cdi]

i shoot a lot of motorsports both indoors and outdoors. luckily i am at venues that have good lighting so i can use the lowest iso setting i can use. ive noticed the better the lighting, the lower the iso i use, the smaller the file size i get the more photos i can take on a single card.