What influences photo size?

[Kermit power]

Evening all,

I've just processed 5 images (which I'm about to load into the Macro thread), all of which were taken with my 7D. They were all shot as RAW files and processed in Elements 11. All were saved at maximum jpg quality, and none have been cropped.

The final jpg files range in size from 12 to 20Mb. Looking at the RAW files themselves, those I took on my summer holiday also vary significantly in size from 17 up to 32Mb. What causes this? Is it just down to how much colour variation there is or something?

[Kermit power]

And at this point, could a kindly mod please move this to the photo forum where I meant to put it in the first place?

[Tuna]

It basically comes down to how 'compressible' the image is. In the case of jpeg, the algorithm likes large areas of smooth colour, and has to work harder on sharp edges and high contrast detail.

The easiest image in the world to compress would be a square of completely flat colour. I can get that down to a few bytes, no matter how 'big' the picture is. Something like "where's wally" is at the opposite end of the spectrum.

[tim-b]

Tuna said:

It basically comes down to how 'compressible' the image is. In the case of jpeg, the algorithm likes large areas of smooth colour, and has to work harder on sharp edges and high contrast detail.

The easiest image in the world to compress would be a square of completely flat colour. I can get that down to a few bytes, no matter how 'big' the picture is. Something like "where's wally" is at the opposite end of the spectrum.

What Tuna says. Basically, the amount of detail in the image is what matters. Low light stuff tends to be the worst, because of the noise, each pixel has a big variation from the next. A simple abstract shot, or one where a large portion of the image is out of focus or blurred will be much smaller.

[Simpo Two]

Better to call it 'file size', as 'photo size' can mean pixel dimensions or physical size when printed.

[GroundEffect]

Yup, noticed over the years that the smoother the colour/luminosity gradients, the smaller the file sizes. My 24MP (D3200) of the moon and the dark sky can be very, very small if running low ISO and lots of noise reduction.