Why is a raw file under 1 megabyte per megapixel?

[Throckmorton]

My Sony A35 has a 16 megapixel sensor at 12 bits which comes out to 24 megabytes. But the files are only 14 megabytes.

My A77 is 24 megapixel at 12 bit (some sources say 14 bit) which is 36 megabytes. But the files are only 20 megabytes.

How is that possible? Is there some kind of compression going on?

 

[Syborg1211]

That's interesting... My Nikon raw files are larger than their rated megapixels. My D600 which has the "same" sensor as the A77 has raw files in the 28-29mb range. My D800E's raw files are around 40mb. There's definitely some sort of compression going on if you consider that each pixel is actually three values because of RGB.

 

[Railgun]

Craw. It's being compressed.

 

[gevorg]

RAW images are not really RAW. Some manufactures even apply noise-reduction when creating RAW files. Hence, "RAW" is a very relative term that varies from one maker to another. Also, RAW contains stuff like file header, metadata, sensor specific data, built-in reduced JPEG.

 

[destrekor]

RAW images are not really RAW. Some manufactures even apply noise-reduction when creating RAW files. Hence, "RAW" is a very relative term that varies from one maker to another. Also, RAW contains stuff like file header, metadata, sensor specific data, built-in reduced JPEG.

To be fair, some, like Nikon, see their RAW files basically stripped of all extra content in most applications, other than in Nikon's own RAW converter software.

 

[destrekor]

Craw. It's being compressed.

Also, this. Lossless compression is sometimes employed.

 

[Rakehellion]

Also, this. Lossless compression is sometimes employed.

Sometimes it's lossy.

 

[destrekor]

Sometimes it's lossy.

I think most RAW-capable cameras default to lossless compression.

 

[Throckmorton]

Oops, I understated my file sizes. They're smaller than 1mb/mp but not as much I posted. There still has to be significant compression though. I'm not sure how it can be lossless considering how complex some images can be. Even a picture with the most possible detail gets compressed the same amount

 

[Throckmorton]

That's interesting... My Nikon raw files are larger than their rated megapixels. My D600 which has the "same" sensor as the A77 has raw files in the 28-29mb range. My D800E's raw files are around 40mb. There's definitely some sort of compression going on if you consider that each pixel is actually three values because of RGB.

Each pixel isn't 3 values, it's only 1 value representing R or G or B-- then software interpolates those into a full res image

 

[shortylickens]

Lossless compression.

Do me a favor, take a pic of a black room, and tell us how big the file is.
I'm kinda curious.

 

[Throckmorton]

Lossless compression.

Do me a favor, take a pic of a black room, and tell us how big the file is.
I'm kinda curious.

I put my hand over the lens and took two pics... Both 23.4mb from my 24 megapixel Sony A77. Then I took 2 normal pics and they were both 23.7mb.

So there does seem to be compression, but it's weird that total black only saves 0.3mb

Edit: I boosted the exposure in Lightroom and there's a lot of noise, so that accounts for the size