Kis összevetés a képtömörítésekről a Google Fotók szuperjó tömörítése kapcsán.

Kis összevetés a képtömörítésekről a Google Fotók szuperjó tömörítése kapcsán.

Originally shared by Paul Brocklehurst (Brock)

Photo compression, and why storing at high resolution is not enough

Something that disappointedly me with the new Google photos service is that it doesn't keep your original photos (and is quite sneaky about it)

What it offers is storage of photos up to 16 megapixels. Thats great right? Most phones (and cameras) have less than that. So what's the catch?

The problem is that Google photos compresses your shots using a lossy algorithm, so data is lost. The resolution is not affected, but individual pixels are. See attached image for an extreme example of compression artifacts.

Ever wonder why photos look bad on Facebook? Heavier compression than other sites. And photographers being obsessive about detail, lossy compression, of any kind , is bad.

I'm sure Google photos uses algorithms at a level most users won't mind, but its not really a true backup of your photos. The higher tier does promise to "store your photos and videos exactly as you captured them."..... For a price.

edit: the compression level according to Google engineer Vincent Mo :
"free storage is 16MP at JPG90, which is higher than the Lightroom default of 75. :)"

edit:29/5/15
Some more from a Googler on compression.  Taken from comments on
https://plus.google.com/+DaveCohen/posts/GGJEt7gUf4A#+DaveCohen/posts/GGJEt7gUf4A
Dave Cohen: the distinction is "original" vs "high resolution" (i.e. more than just counting megapixels). Original, no matter what size of the image, will keep the original bytes and I suspect will count against your quota. The high resolution option gives Google the ability to utilize compression that reduces file size but keeps the image nearly indistinguishable from the original. If you care about using Google Photos as a backup solution and need the ability to get the exact bytes back, then the "original" option is the one you want. For most users the "high resolution" option will be more than good enough.