I exported a JPEG photo with a file size from the camera of 2.3MB. I set the export settings to JPEG, 6 in. X 4in. and a DPI of 300. Got a file of 1.3MB. Did same with tiff 16 bits and got a file of 11.5MB. For whatever reason, neither file correlates to to the file size I started with. When you double the size to 12 X 8 and do the same thing with JPEG, you get 4.5MB. Non of this correlates to the original file size. What am I missing?
Jay,
I’m not sure I completely follow. The original file size of 2.3 MB is irrelevant; JPEG sizes vary on compression level used (quality 1-12), and also based on the content of the image (an image of a mostly solid-blue sky will compress much more than an image of a busy street).
A JPEG at 6” x 4” @ 300dpi is 1800x1200 pixels, which when compressed to JPEG, coming out at 1.3 MB seems reasonable.
TIFF is different of course as it’s not compressed, and if you open Photoshop and create some new files at various sizes, you can see how sizes change quickly.
Here’s a 6” x 4” @ 300 dpi file, 8-bit; 6.18 MB (no compression): [screenshot]
Here’s the same 6” x 4” @ 300 dpi file at 16-bit; it’s 12.4 MB: [screenshot]
And now here’s that 16-bit file, doubled. Remember, doubling each dimension is actually quadrupling the file size; it’s now at 49.4 MB: [screenshot]
I hope this helps,
-Joseph @ApertureExpert
@PhotoJoseph
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