File size of corrected jpegs expands to half the size of the original

Question

Using a Canon 1Dx, I have an option of utilizing both slots and assigning different file types to each.  In one slot I shoot RAW, and on the 2nd slot I shoot a JPG backup.  Typically though I'll do all my work on the RAW file in Lightroom 5.  The unimported JPG shot on the second slot expands to approx. 51MB.  But the CR2 file, imported to Lightroom 5 and then exported as a corrected JPG, only expands to 28MB.  Am I missing something on import/export that would reduce the filesize of the corrected JPG?  I cannot find a setting that is toggled that augments import/export size.  Is this a bits per channel issue?   Similarly, I have the same issue with Bridge.  When converting a CR2 file to JPG it expands to the same 28MB filesize.  My client wants his JPG to expand closer to that 50MB number.

Answer 1

dean5432 wrote:
When the JPG file is opened, it shows as 51MB.  When the CR2 file is opened it's 28MB.  I was under the mistaken impression that the files would produce equally sized JPGs, and that somehow in the output from Lightroom it was constraining the size of the finished image.
When you say "opened" what  'MB' reading are you reffering to? Lightroom can show the image file's Resolution (5184 x 3456), File Size (MB), and Megapixels. What does LR show for these three reading, in particular you should be interested in the image 'Resolution' value.
When viewed in PS your Canon 1Dx raw image files should show a 'Document Size' of:
5184 x 3456 x 3 (RGB) x 2 (16 bit data) = 107,495,424 Bytes ÷ 1,048,576 (# of Bytes in MB) = 102,515,625 Bytes = 102.5 MB
Your full-size Camera JPEG images should be exactly 1/2 since they are 8bit images = 51.3 MB
I can confirm these numbers with my Canon 600D, which also uses a 5184 x 3456 resolution sensor.
You may have your camera set to shoot M-Raw (3888 x 2592) or S-Raw (2592 x 1728) with full-size JPEG (5184 x 3456).