File Size & Dimension Size for Enhance PNG

[KostFan2]

• Background:
• a) Relationship: In general, I thought that an image’s dimension size and file size were related.  The larger the dimensions, the larger the file size would be.
• b) Compression: I understand that PNGs are “lossless” vs. JPGs which have a high degree of compression applied.  Therefore, a RAW image exported in Photoshop as a JPG is expected to have a SMALLER file size than exporting it as a PNG (for the same file content).
• Questions:
• Enhance PNG Dimensions: When I run enhance (super-resolution) on a RAW image (30.0MP = 6744 x 4502)  in Photoshop the file dimensions are much smaller (0.7MP = 1024 x 683) than the JPG created by exporting the same RAW file as a JPG (30.0MP = 6720 x 4480).  I understand why the JPG has a smaller file size (6.3MB) than the DNG (94MB) because of both:
  1) compression for JPG vs. Lossless for PNG and
  2) super-resolution applied to the PNG.
  However, I do not understand why the PNG image dimensions are so much smaller than the JPG.
  Can anyone explain why?
• Repeatable: I have that same result when I do this for over 1,000 images.

[D Fosse]

PNG compression is less effective than jpeg compression. So a jpeg will generally be smaller - but jpeg compression is lossy and non-reversible. So permanent degradation is the price for the smaller file.

Jpeg compression is highly dependent on image content. Flat areas compress much more effectively than busy high frequency detail. So there is no direct relationship between pixel size and file size. It can vary by a factor of 10 for the same pixel size and same compression level.

The long and short of it is that for compressed file formats, file size on disk is unpredictable.

I've no idea what you're doing with Super Resolution. It will double the linear pixel dimensions, producing 4x the total pixel count. This has nothing to do with what format you're saving it to later.

[KostFan2]

Dear d Fosse:

Thank you for the quick response.  The DNG file is automatically created by either Lightroom or ACR when I run enhance.
I do not understand why the dimensions for the file are appearing much smaller 0.7MP (1024 x 683) than the JPG created by exporting the same RAW file as a JPG 30.0MP  (6744 x 4502).  The Magnitude of the difference is the cause for my question (JPG is 43x larger), especially when the DNG file size is so much larger (15x).
This same result occured for 1,000 images