I have my Nexus5 set up to automatically back up my images to Google photos. On my phone there are 2 options for backing up photos:
High quality
Great visual quality at reduced file size (free unlimited storage)
Original
Full resolution that counts against your quota
I am currently using the High quality setting.
I decided to perform a spot check of a photo on my phone vs. the same photo online:
- Phone – file size 1.71MB
- Online – file size 1.18MB
Then I compared the stats of the photos in Windows explorer – both are identical:
How is Google reducing the file size for the backed up photo?
Best Answer
Google will be resampling the image using a higher level of compression (which your stats don't show). The quality of the image is likely to decrease slightly, although whether this is noticeable to most people is another matter.
The "quality" (a scale of 1 lowest to 100 highest) factor is part of the JPEG algorithm. Reducing the "quality" increases the effective compression. Applied intelligently, small reductions in the "quality" (at the upper end) can result in significant savings in file size without any changes in the perceived image. This generally works OK with photographs, which is the intended image type.
Also, if your images are larger than 16mp then Google will reduce the physical size of the image to 16mp. See Choosing a storage size.