Photo resizing versus photo compression
A visitor of this web site wrote:
"My roommate, thinking to help save space, compressed my photos and saved them at the new smaller size. How can I undo it?
First it is important to note that photo compression and photo resizing are 2 completely different things.
When compressing a photo (jpg), you keep the same image size, that is width and heigth in pixels won't change,
but you get a smaller file size in kilobytes by losing quality (think about it like bluring small details).
When resizing a photo, the resulting image size in pixels is different, mostly smaller, but it could be bigger.
Unfortunately neither photo compression nor photo resizing can be undone, since a part of the original information is lost and can not be retrieved by magic.
You can resize your photos to make them bigger again by interpolation, but it is not advisable.
You won't have the quality of the originals, since the information lost when resizing them to a smaller size is really lost and can't be re-invented anymore.
The only little hope one can have, is if one has backup copies of the originals on cd-roms, an external hard-disk or on another support.
Another little hope would be, if (and only if
) the names of the pictures have been modified while resizing them,
then the originals or a part of them could still be in the trash bin.
Many people, and I too, now have an external hard-disk of same capacity or even bigger than the internal hard-disk,
just for one thing : to keep backup copies of all the work we have done.
Often the necessity of backups is not recognized before an important loss has occured.
Now let's have a look at some examples.
Example of resizing
This is resizing, a reduction from 300 x 225 pixels to 150 x 112 pixels.
Example of compression
This is compression, a quality factor of 85% and a quality factor of 10%.
To not produce a page that takes too long to load, I did put some larger examples on separate pages. Have a look at them !
Examples of a photo with various compression factors
(or quality factors).
Example of a reduced than re-enlarged photo