This article, in three parts, will discuss the most popular File Formats and how best to use and save files using each format. And then finally, how to Resize and Save your Photo Files for the best possible use, here on Photographica and elsewhere on the web.
Part one, JPEG's
Please note, The following is as I know it and understand it from the Reading I have done and even the Experiments I have tried. This is all from my head and not just cut and pasted from a web-site. So if you find errors or disagree, bring it up in the comments for everyone to see and learn. There are some parts that are not Technically perfect, but I have tried to explain so everyone understands not just the engineers here
I have decided to break this down into three parts so it is smaller on the page and also so you don't fall asleep and get bored. The First two parts will be mostly Techno-babble but the last part will be simple recipes for different skill level to achieve better images for both print and most importantly, sized correctly and clearly for posting on Photographica
Let's first start with a little talk about JPEG Photos the most common Photo file type. JPEG's are a "Lossy" Compression File type. All that means is that each time a Photo is Opened, Edited and Saved, some information is "Lost". Ever notice that you may have a 8 MP camera but when you look at the Photos you downloaded in your computer, the file size is only 3.2MB. What happened to all those extra bits and pixels? Well because of how JPEG compression works it actually throws away information when the photo is saved, reducing file size but degrading the picture slightly but not so much that it is visible to the eye...But how it "throws away" information is important. If it just discarded Pixels the image size would shrink. What it does is; instead of showing every pixel's absolute color it will look for a neighboring color that is close enough and use that color thereby limiting the information needed and making the file size smaller. These changes are not perceptible to the eye for the most part. The first or so time around...
But as I mentioned before each time you Open, Edit and Save you will be throwing away much needed information and soon you will begin to see the nasties of JPEG Compression Artifacts.
Here is what a properly Saved Photo looks like and one saved incorrectly with Compression artifacts in it.
JPEG Compression Artifacts
Notice The Jagged edges and the "Moiré Pattern" in the blue sky. That is the effects of using the closet neighbor color instead of the actual one and the effects of compression
Let me just explode a common misperception here. If you just open and save a JPEG file or do multiple saves (NOT save as) during an editing session, providing you use the exact same amount of Compression as originally used, it will NOT degrade your image. It is only when you open, edit and save will you introduce more noise into your Photo.
Here is the same section of the photo one the original, the second after 10 cycles of open and saves magnified 300%. There is no visible difference even though some loss has occurred.
JPEG 10th Generation Magnification 300%
Any time you edit a JPEG photo and change pixels in any way, Cropping, Sharpening, Contrast, and Saturation and then save there will be some degradation to your image. One exception, if done properly, will not degrade your image quality; rotating the image. Do this outside of any image editing software. If you just right click a photo in you file folder you can rotate an image without degrading it. If you do it within an Image editor there will be some loss.
So after all this degradation will it be perceptible to the eye? Maybe not if you follow some easy steps.
* Start with the best image possible. In your camera, set your image size to the largest size and the lowest Compression (Fine, superfine etc). If you are going to be throwing away information later you might as well start with the most information. (One exception would be if you ONLY use photos to the web or e-mail and you are limited in File Storage Space. But, you still will be throwing away information from your Digital sensor)
* Do all your editing with the image at full file size (Not re-sized for the web), again more information available.
* Do all your editing in one session, (If you cannot do this, see the section later on TIFF and Photoshop Files). The more times you separately open, edit and save. The more degradation your image will have.
* Limit your Cropping, When you crop an image you will throw away Pixels so there will be less to work with and you will need to re-size the photo to it's original size (In most cases) for Printing so you will magnify any flaws in the image. Try getting your cropping or framing right when you shoot the image.
* Save the image at the Highest Quality or least compression available (we are not talking saving for the Web, yet) and always save at the same Quality. Switching to a lower quality will degrade the image, saving at a higher quality will increase the file size with absolutely no increase in quality.
OK Coming up,
Part two: Tiff and Photoshop Files
Part Three: Three recipes for Three Experience levels for Better Images for both Printing and the web
