JPEG files can be wonderful things. They pack incredible amounts of information into a very small package. You can email them to your friends, your clients, your printer, and a thousand other places all across the world at the touch of a button. Those of us in the design business have to deal with them almost every day. But they have their limitations, and if you have to handle them professionally, it pays to know and understand those limits.
Most clients and contacts that I work with are quite knowledgable about JPEG files. But every so often I run across “professional” people who are… well… just plain clueless about them. I find that annoying, and unfortunately it happens with some regularity. So without pretending to be an expert, but simply in the spirit of combating JPEG illiteracy, the following list touches on just a few JPEG myths and misconceptions that I’ve run into in recent months:
–JPEGs are always lo-resolution. FALSE.
–JPEGs are always hi-resolution. FALSE AGAIN.
I’ve heard it both ways from different sources, but the fact is, they can be EITHER. This is the primary misconception I hear about JPEG images, and I’m amazed how often I still hear it. Images intended for the Web are lo-res (typically 72ppi). Images destined for offset printing are hi-res (300ppi or better).
–JPEGs are always RGB format. FALSE.
I hear this one a lot too. JPEGs can be RGB, or CMYK, or even grayscale.
–JPEGs are great for both print and web use. FALSE.
They are great for web use, but for print work JPEGs have to be decoded by the RIP processor, and will often cause your job to run more slowly in prepress. Better to use CMYK TIFF or EPS format for importing into your print layout software.
–JPEG is a destructive format (TRUE) and therefore always bad (FALSE).
This is a debate that will rage on endlessly, and most of the gripes I hear come from photographers. But for hi-res images, it is this designer’s opinion that so long as you’re careful when and how you save your JPEGs, the damage that’s done to them is typically very minor and for the most part not detectible by the human eye. JPEG is indeed a destructive format (lossy compression it’s called). But on hi-res images saved at high quality settings, the deterioration is very difficult to detect. (File size increases dramatically at higher settings, so depending on what your prioritites are, keep that in mind.) Note also: the lower the resolution of the image, the greater the visual degradation to the image at a given quality setting. In other words, lo-res images take a proportionally bigger beating from JPEG compression than hi-res images do.
One caveat: JPEG compression can cause subtle color shifts in some tonal ranges, so images with precise color requirements should avoid JPEG compression altogether.
–JPEGs are damaged every time you open them. Nope… FALSE.
The simple act of opening a JPEG file does absolutely NO additional harm to the image. Nor does importing it into a layout program. It’s the SAVING of a JPEG image in editing software that causes the damage. For example: you open an image to look at it, and then close it–no damage. You open an image and edit it, then save it, then close it–you’ve done damage. Open it again, do more edits, and save again–more damage still, and worst of all the damage is cumulative–it gets worse with each additional open-and-save session. (Interestingly, if you open an image and save several times during editing, the damage to the image does not accumulate with each save during the same editing session.) Hmmm.
So, if you intend to edit your image at any time, you’re better off keeping it in a non-lossy format such as TIFF, PNG, or BMP until you know for sure there will be no more edits. At that point, you can save the final image ONCE to the JPEG format, thereby doing minimal damage to the image.
That’s it. Not a comprehensive list of information by any means, but it hits some of the main points that I run into over and over. Hopefully it’ll be helpful to someone somewhere along the way.