Pixel Dimension OM??

[Morris Man]

Hi

I'm new to Lightroom so excuse the query if it's an obvious one! I have exported a RAW file in Lightroom, saved as a .Jpeg and opened up in Photoshop. When I go to Image Size I am seeing Pixel Dimensions in OM? I have never seen this abreviation before, I was expecting to see MB.

Any help will be much appreciated.

[Hal P Anderson]

That's 144.0  M, which I assume is megabytes.

Hal

[elie_dinur]

"That's 144.0  M, which I assume is megabytes."

To be more exact: it is the image size in memory as an uncompressed 50.32 MP 8bit image. What we call an "8 bit RGB image is actually 8 bits per channel and since 8 bits = 1 byte that makes 3 bytes per pixel.

50,320,896 pixels X 3 bytes = 151 million bytes and after allowing for the fact that 1,024 bytes = 1 KB and 1,024 KB = 1 MB we get 144 MB. This is the size that the file will be if it is written to disc as an uncompressed "8 bit" Tiff or PSD. Because a Jpg is always compressed, it will be much smaller.