The only workaround is taking a screenshot of the edited image in photos to keep the mb size up.
So when you refer to size you mean the 'weight' of the file, measured in kb or mb?
If so, it's a little bit complicated.
- Size, in Photos (and most photo apps) means the dimensions of the shot, measured in pixels. There is no direct correlation between pixels and megabytes.
- Quality is the expression used for the 'weight' of the file. Higher quality jpegs means larger file sizes.
- Dragging from the Photos window yields the Preview of the image. This is a medium quality version of the edited shot, intended for when you share the image to another app, like sending an email to Grandma or popping something into a newsletter
- Option-dragging yields the original unedited image
- To get a high quality version of the edited image you need to use the Export command - File-> Export
- In the resulting dialogue you have several options but the relevant one is quality. Higher settings give you heavier files.
- Here's an oddity: it's even possible to export images that have higher quality (or weigh more) than the original. Not that Photos is adding data to your image, it's just applying less compression to the jpg than your camera did.
Incidentally, it's pretty much impossible to export an edited photo at the same weight as the original because of the variance in compression algorithms. If you do then it's a fluke.
