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That MP to MB calculation is slightly off  - your method can be used to derive the total number of bytes but you have to divide by 1024*1024 to get MB (a 6 MP image is approx. 17 MB, not 18 MB). Also,  I don’t believe (although open to argument) that PPI means a whole lot in image terms as the physical size of what you view depends on, and only on, the resolution of the monitor – it does make a difference when printing though which is more a DPI thing



You are correct of course in relation to the MP to MB calculation but I think the integer approximation is pretty reasonable for most practical purposes.


As for the dpi thing, this doesn't arise on this forum but I've seen it cause a lot of confusion years ago, particularly when people were scanning at 4000 ppi or whatever and then converting to 240 or 300 ppi in Photoshop and then having to set the printer resolution at say 1400 or 2800 dpi. Guidance documents would frequently just go for dpi for all 3 which is clearly incorrect and potentially confusing.


It doesn't really rate at the annoyance level I quoted though - tailgaters and drivers who block me in completely by inconsiderate parking and then refuse to move rate much higher than erroneous use of terminology really. I do wish that the professionals producing guidance documents would get the terminology right though. 

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As a computer scientist and photographer I've a foot in both camps (MB and MP). I've also spent time on standards committees drafting industrial standards. A key aspect of a standard is that it should allow clear and concise communication that is easy to understand as practical by all potential users.


So I'm with Woody on this one. Whilst MB may be the "industry standard", in my opinion it's a poor choice. MP would be much better. You only have to look at the number of questions raised in this forum by photographers on this topic to see that using MB is not the best method of communicating the image size requirements. Using MB risks confusion as a result of varying bit depth (8 or 16 bit) and image compression levels as well as being a derived value. I prefer to quote either MP or pixel dimensions, but will happily work to any requirement. (I've had requests for physical size at 300PPI, MP, MB and pixel dimensions).


That's my two penneth worth  (FX runs for cover).

I agree with you but there is no chance of this changing in the near future I would guess. And as somebody pointed out above, the main source of confusion is the JPEG compression giving a much smaller file size on disk. 

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