Andrew Kelsall | Graphic Designer

When I was at University about five years ago, I was designing a CD cover with some Jpeg photographs and was constantly changing the images and re-saving them for use. However, after a while I noticed that the images began to degrade with each save.

Back then, I didn’t know much about Jpeg (Jpg on Macs) files—and the fact that they were a compressed-format. Before I explain further about this, I thought I’d show the gradual degradation of a Jpeg image after each re-save as another Jpeg…

The above image shows the original version of my file—a photo of my English Springer Spaniel, Bayley, (being held by my wife) when he was a just little puppy…cute!

After the first save, some detail in the red carpet texture has already been lost. Already, a slight ‘blocking’ has appeared around the AndrewKelsall.com text.

On the third save, the blocking effect is slightly more prominent around the text.

As the blocking effect continues, slight color changes appear in Bayley’s ear and the purple robe.

Definition is now slowly been lost around the eyelids—and the speckles on his nose are becoming muffled.

The tirade of the Jpeg blocking effect starts to take hold of the photo as a whole.

As the degradation continues, the blocks became extremely visible .

As Bayley’s whiskers start to disappear, he’s not looking as cute as usual!

Bayley looks on as the photo slowly compresses into Jpeg blocks, with stripes appearing within them.

At the final save, his whiskers have all but gone, major details are lost—looking more lego-like than photographic.

As can be seen in the comparrison above, the Jpg saved 10 times over has obviously lost much of its quality—and some color changes.

So why does this happen? In a nutshell, every time a Jpeg is saved, it is compressed—this is why Jpeg file sizes can be very small. In the examples shown above, I used varying degrees of compression, ranging from 18-79%. This, I summise, can generally show what a Jpeg could look like if 10 different people re-saved the file after editing, with various choices over compression amount. For an in-depth insight into how exactly Jpegs work, check out this Developing for Developers article. (As a side-note for anyones who’s interested, Jpeg stands for the “Joint Photographic Experts Group”—named after the folks who developed this format).

So, if you are a graphic designer, photographer, etc., it’s worth considering the consequences or re-saving a compressed Jpeg image. The above example shows an extreme example of the kind of degradation you could expect from saving the same image with no alterations. If I added elements, changed colors and re-sized the image throughout the process, the end results would be much worse.

So, how shocking can a Jpeg be? Very, it would seem!