At AdoramaPix we offer two formats for uploading your photos to us - JPG and TIF. Jpg is a lossy format, while TIF is a lossless format. Some of our customers don't understand the difference between these formats so we will attempt to explain in laymans terms.
TIF - Lossless Compression
Lossless image compression means that all the data from your original photo is preserved. Some photographers, professionals in particular, tend to prefer this format because they feel that it will preserve their photo exactly as they took it - which it will. The downside to this format is that the files are HUGE.
JPG - Lossy Compression
Lossy image compression means that the size of the image is reduced by some means of compression. Jpeg images use what is called transform encoding, in which small blocks of the image have their colors averaged out to create an image that has fewer colors than the original. i.e. lets say a dark portion of the photo has a block of 4 pixels side by side that are virtually the identical shade of black - they will be changed to the exact same shade of black, a change that cannot be detected by the naked eye, but allows the file to be made smaller.
Which is better?
So here is the bottom line for most customers - can you see the difference? If you choose the maximum quality/minimum compression of a JPG file, I would argue that the difference is imperceptible. i.e. you wont be able to tell the difference unless you're looking at your image under a magnifying glass AND have the original next to it to compare with, and even then, it would be extremely hard to spot differences. And yet, even a minimum compression jpeg file would still be about 1/3 to 1/4 the size of the same image saved as a TIF.
In other words, save yourself the time it would take to download massive TIF files and use the JPG format at maximum quality. Your pictures will still look perfect, and the time you save you can spend doing something more entertaining than watching a loading bar move across the screen.