I take a photo in 'portrait' mode, I download to my Computer, At the photo which downloads in landscape mode it says 5472 x 3648 = 6.20 Mb.

 

I rotate the photo so i can see it on it's proper portrait mode and the photo now says 3648 x 5472 but the size is now only 5.61 Mb.  Why?

Edited April 14, 201511 yr by Billyboy294

It's because the pixel density of the horizontal pixels is a bit less than those of the vertical ones. The original ieecm specs were made with analog cameras in mind, so even though it's not necessary in the digital world, the density was less. Hopefully this will be resolved with the new 4k specs soon to be issued.

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Fuck me, I just made that bullshit up.

 

Tried to make it slightly plausible, but nonetheless expected to get called a liar and then I'd have admitted it.

 

Good job guys making me feel bad by not calling me out.

The most likely explanation is that the tool you're using to rotate the picture is re-compressing the image to an extent that it results in a smaller file.

 

You could likely adjust the compression so that the resulting file comes out much larger, too.

 

Your logic is sound - after all, after rotating, you have the same pixels with the same relationship to each other (an important detail when it comes to compression), right? It IS possible to do a "lossless transform" on a jpeg, but you'd need to use a tool that supports this. 

i think in the landscape more pixels than portrait mode

The most likely explanation is that the tool you're using to rotate the picture is re-compressing the image to an extent that it results in a smaller file.

 

 

Assuming its a jpg file this will be the reason. Unless you are using the photo for professional purposes (in which case you should not be storing in jpg) then the file size reduction won't make any noticable difference.