High ISO = Less Card Space?

[peety3]

What's really funny is that it's unnecessary. For example:

• ISO 1600 - f/4 - 1/500 - 25 MB
  
• ISO 25,600 - f/4 - 1/500 - 45 MB

Both shots have the exact same exposure. The noise is the exact same
too (after you correct the brightness in both images to be the same),
which is no surprise given that ISO 25,600 is just a digital push of
ISO 3200. It has 4 stops of clipped highlights, so it actually has less
image data, yet it's almost twice as large. If Canon offered Metadata
ISO, the filesize could remain the same, and the highlights would not
be deleted needlessly.

You never said whether these two bulleted examples were of
the same subject matter. You only said this was two different
images/files. You said both shots have the exact same exposure, which
we could see plainly by reading the text.

They have the same exposure data, which suggests to me that the second shot had less light (maybe 16x less light).

They have the exact same "exposure", which means the exact same amount of light. (The "data" value is not part of exposure; it is part of "brightness"). The ISO 25,600 shot has a four-stop (16X) increase in gain, so the data values are 16X higher than the ISO 1600 shot, even though the amount of light is the same. The SNR is the same too, but one must equalize the brightness for a visual comparison.
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Jesus, do you have to pick apart every post word by word? If you had a tool that could show you the 1s and 0s related to a particular picture/image/whatever YOU want to call it on your memory card, there'd be some data in that file that would tell you the exposure 'specifications'. Based on your previous posts, you define 'exposure' to be shutter and aperture. I consider that to be data (it's expressed in 1s and 0s, and varies picture-by-picture), and it happens to be data about the exposure, so I called it 'exposure data'. There'd be millions of 1s and 0s that represent what the camera considers to be the actual image, I'd consider that to be 'image data'.


And the same "exposure" in no way signifies that it's the exact same amount of light. I can set my camera to manual exposure, f/4 and 1/500, and shoot all day long. There's no inherent likelihood that any two pictures would have the same amount of light. I could also shoot in Av f/4, and when I see a shutter speed of 1/500th I could lock exposure, to take just two pictures. However, if I'm shooting in Av f/4 and take a shot when in ISO 1600 and see a shutter speed of 1/500th, I'm going to assume that the camera chose that speed based on what the meter interpreted of the scene. If I'm shooting in Av f/4 and take a shot when in ISO 25,600 and see a shutter speed of 1/500th, I'm going to assume that the camera chose that speed based on what the meter interpreted of the scene. Chances are, the second example shot (i.e. f/4 1/500th with an ISO selection of 25,600) was taken in 1/16th the light (within the parameters of the metering mode selected) as the first example shot (i.e. f/4 1/500th with an ISO selection of 1600). But guess what? They've got the same exposure (and you'll find the same exposure data in each image file). Big whoopdedo. As a result of the difference in light seen by the meter and sensor, I'm expecting higher noise and larger file size, OK?


Why do I come here?