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## Pixel Dimensions math

### Jan 2, 2012 3:53 PM

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I'm uploading vector illustrations to a stock site. They want an RGB JPG file of the vector that is 2800 x 1900 pixels, or the equivalent pixel dimensions. They say that since 2800 x 1900 = 5.32M, the image can be any size, as long as the hieght x width are equal to or greater than 5.32 million.

So in the attached screen shot, why are my pixel dimensions 15.2M instead of 5.32M?

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Jan 2, 2012 5:20 PM   in reply to SneakerG

5.3 Megapixels == 15.2 MegaBYTES of image data in 8 bit/channel RGB

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Jan 2, 2012 8:30 PM   in reply to SneakerG

Yes, Megabytes are counted in Megabytes, not millions.

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Jan 2, 2012 9:25 PM   in reply to SneakerG

SneakerG,

While I would never presume to speak for guru Chris Cox, who has been writing Photoshop code for some 16 years or so, the fact that I have no connection to Adobe allows me to agree with you publicly that the Image Size dialog box appears indeed to be mislabeled on its face.  That "15.2 M" figure should read 15.2 MB.

The pixel dimensions are evident:  2800 pixels wide x 1900 pixels high = a 5.32 Megapixel image file.

Now, to get the Megabytes you multiply the 5,320,000 pixels by 8 bits x 3 channels.

http://en.wikipedia.org/wiki/Megabyte

The megabyte is a multiple of the unit byte for digital informationstorage or transmission with two different values depending on context: 1048576 bytes (220) generally for computer memory;[1][2]and one million bytes (106, see prefix mega-) generally for computer storage.[1][3] The IEEE Standards Board has decided that "Mega will mean 1 000 000", with exceptions allowed for the base-two meaning.[3] In rare cases, it is used to mean 1000×1024 (1024000) bytes.[3] It is commonly abbreviated as Mbyte or MB (compare Mb, for the megabit).

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Wo Tai Lao Le

我太老了

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Jan 2, 2012 9:40 PM   in reply to SneakerG

As for Pixel Dimensions, those are expressed as so many pixels wide by so many pixels high.  Period.

If you multiply those two dimensions, you get the image size in Megapixels, not to be confused with the image file size in Megabytes, which takes bits per pixel per channel and number of channels into account.

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Wo Tai Lao Le

我太老了

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