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Al Fasoldt's reviews and commentaries, continuously available online since 1983

JPEG? GIF? TIFF?
The image format blues: How to know which one to use


Oct. 30, 2001


By Al Fasoldt
Copyright © 2001, Al Fasoldt

   I explained a few weeks ago that JPEGs should be considered bad news for anyone serious about digital photography. But what about GIFs and other image formats?
   This is a good time to tell you what's right -- and wrong -- about those other kinds of images this week. You might be surprised.
   The basic JPEG conundrum is this: Saving your pictures as JPEGs strips out parts of your photos. JPEG processing makes image files small by removing detail. It's done in a clever way, so most of the time we don't mind.
   The problem -- and the reason I have been telling you to avoid JPEGs when you're editing your pictures -- can be summed up in one word: Loss. What you lose when a JPEG image is saved can never be put back in the picture.
   That's why JPEG is called a lossy image format. It losses things. And it's why Lossless methods are essential. Never do any fixing, editing, cropping or adjusting to a JPEG image. Always work on a lossless version and save the results in lossless form.
   The most common lossless format for Windows is BMP. But BMP (pronounced bimp if you don't mind snickering from the other side of the room, or Bee Em Pee if you do) has a major liability. It's a non-compressed format. It's lossless but its files are big.
   As I explained previously, PNG (Portable Network Graphics, pronounced ping) is the up-and-coming solution to the problem of compressing images without changing them. PNGs are lossless, just as BMPs are, but they have much smaller file sizes.
   But as soon as I wrote about PNGs, I heard from the GIF crowd and the TIFF folks. They made some good points, so we'd better explain why GIF and TIFF might make sense in some situations.
   
    GIF stands for Graphics Interchange Format, an image method owned by CompuServe. (It's pronounced "jif" by most of the world, although Mac users sometimes say it with a hard G as in "garage.")
   GIFs were the pioneers of Web images. Long before JPEGs came along, GIFs were all over the place. They're still popular, but they're dreadful for pictures of you and me and Uncle Ben. They just don't work for photos.
   GIFs are ideal for images that have a lot of sharp edges -- for anything that has text (letters and numbers) in it, for example. GIFs preserve all the precise shapes in an image, so they're perfect for Web-page billboard ads (those are mainly text, right?) and for the large headlines you see on Web pages.
   JPEGs are terrible for images that contain text, and they're useless when you need to show sharp, clear objects.
   
   Look at the main page on my Technofile site for a good example. The word Technofile is large and very clear. It's a GIF image. You can see two smaller versions of that identifying image, called a logo, alongside this article. One is a GIF, just as clear as ever, while the other is a JPEG, fuzzy and ugly.
   We forgive JPEGs for this behavior because our eyes are very forgiving -- and because pictures of people and other real-life scenes usually don't have sharp, clearly delineated edges. JPEGs work by futzing things where one group of colors meets another. They smudge up the edges of objects to hide the fact that details are missing.
   That works for Uncle Ben's beard and Baby Julie's rattle, but it's bad news for the letter T in Technofile. Smudge that up, pal, and you're in big trouble. Likewise for any object with sharp edges and clear shapes.
   
   GIFs rescue us from vision problems while keeping Web pages slim. But they can only do that when they're used for text and similar items, not for photos. (One similar item that cries out for the GIF treatment is a cartoon. If you're going to put a cartoon or any other kind of line art on your Web page, save it as a GIF first. GIF is perfect for cartoons, drawings and maps.)
   (What follows is a technical explanation of how GIFs are different from JPEGs. You can safely skip it if you just want to get on with your life.)
   The JPEG image-compression format makes file sizes smaller by trimming out a great deal of detail. It does this by removing pixels. Of course, if the JPEG processing did this willy-nilly, we'd all be unhappy; Aunt Minnie would look like a rubber duck. So instead of stripping these pixels out in some sort of regular pattern -- three out, one in, four out, two in, that sort of thing -- JPEG processing does it randomly.
   There's a lot of dreary technical detail in the way it does this sort of random chop-chop stuff, and I understand it about as well as I do the U.S. Tax Code. So I'll just point out that the JPEG method uses the Mike Tyson approach: It's brutal in the way it gets stuff out of the way.
   
   What you need to remember is not that it takes out a lot of pixels (and not that it does it the Mike Tyson way -- he's just a brute after all), but that JPEG processing takes advantage of randomness.
   GIF processing is the opposite. It takes advantage of sameness. (I know this sounds too simple. But it's true.) That means two things: First, images with a lot of sameness give the GIF process a chance to strut its squeezin' stuff, and, second, images that are mostly random make the GIF process beg for mercy.
   No kidding. A picture that shows a few clouds floating in an expanse of blue sky doesn't have much randomness (although the shape of the clouds might be perfectly random in some ways), but it sure does have a lot of sameness. Voila! (Or, as my musician friends say, Viola!) That picture would be a good candidate for a GIF.
   Right?
   
   Aw, I hate times like this. I feel like I'm in a Monty Python routine. (How come I never get to feel like I'm in a Benny Hill routine? Life isn't fair.) I hate times like this because I feel like I set you up for a punch line at your expense.
   Here's why. That picture of a lot of sky and a few clouds, the one with a lot of sameness, would indeed be a good candidate for a GIF instead of a JPEG -- if GIFs could only deal with colors properly.
   But they can't, and so it isn't.
   GIFs can show any color among a range of 256. (Technically, that's not strictly true, since the limit of 256 includes black, which is not a color, and white, which is also not a color. Black is the absence of color and white is all colors mixed together, at least when you are dealing with additive color theory. Don't get me started on this. I might never stop.)
   So forgive me if I say that GIFs can show 256 colors even if the total is 254. Everybody else calls 254 colors 256. So, in a world where 2 X 4 pieces of lumber aren't really 2 inches thick and surely aren't 4 inches wide -- go out and measure some if you don't believe me -- we can forgive anyone who thinks 254 is the same as 256, at least for now.
   Besides, that's a lot of colors no matter how you do the math. Surely, 256 colors are enough for any picture. Especially a photo of the sky, right? I mean, blue is blue, more or less. Right?
   
   Nobody needs to make much of a point about this any more. In the bad old days of personal computing, most computers couldn't show more than 16 colors, and we considered ourselves lucky if we had fancier computers that could show 256 colors. But when 256-color displays became common, we stopped fooling ourselves and realized we needed more. Having only a total of 256 colors is just plain inadequate. It's totally weird. It's dumb. It's not enough.
   That's because the blue you see in the sky isn't some computer manufacturer's idea of blue. It doesn't fit into a color wheel with 16 pie slices of color. Or one with 256 tiny wedges of color.
   The blue you see in the sky is God's idea of blue, not quite this shade and not quite that one. It's not the kind of color that can be depicted on the Sherwin-Williams label. It's a natural color, and natural colors seldom fit into a 256-color straight jacket.
   Showing azure blue, God's own shade of azure blue, in an image limited to 256 colors just doesn't work. Likewise for that wonderful shade of burned crimson you see in the fall. Or that subtle yellow-brown tint you've seen in faded azaleas. Or that chromium hint in the sharp brown on glistening coffee.
   
   Natural colors can't be portrayed by a limited palette because they range all over the spectrum. Showing real colors means you have to show REAL colors, not a paint-by-the-numbers selection of one person's idea of blue and someone else's notion of green or red.
   Our eyes aren't easily fooled, either. They need a lot of real colors -- 50,000 or more for starters, and probably a few million in most cases -- to be convinced that they are looking at real scenes. (Don't confuse things by assuming that black-and-white movies and videos -- if you can still find them! -- prove that we don't need color for realism. Our eyes actually see black-and-white images as multi-shaded gray scenes. These black and white images aren't really black and white anyway; they're grayscale images. Confused enough? Let's move on.)
   So any image format that can't show more than 256 colors is a bozo when it comes to photographs. For photos, you need something besides GIF. (Hint: If you're still using a 256-color display on your computer, get with the program. Raise it to the next level, please.)
   Why, then, should anyone use the GIF format at all? Remember what I said about how great GIFs are for text? Tell me, how many colors do you need for the word Technofile? One is fine, thank you. And that one color doesn't have to be Arctic Cheroot or Portnoy Mauve, either; green will do fine, thank you. So a GIF's limit of 256 possible colors means nothing for a Web-page image that shows text. (Even a colorful GIF showing text isn't likely to have more than a few colors. It surely won't have 256.)
   
   Another kind of image that's ideal for GIFs: Cartoons. (A tip: When I say cartoons I am talking about line drawings in general, not just cartoons. Line drawings are pencil or pen drawings -- or their computer equivalents -- and any other kind of artwork that has only one color, generally black.) One-color artwork, cartoons and line drawings are ideal for GIFs; they're reproduced flawlessly. Likewise, maps are perfect candidates for GIFs, too. Maps have sharp, clear lines, simple colors and text -- the three kinds of items GIFs handle so well.
   Everyone who has been assuming that Web pages should always use JPEGs should be doing cartwheels at this point. The lesson is clear. Don't use JPEGs for images that contain text. Don't use JPEGs for line art such as cartoons, drawings and maps. JPEGs are for photographs only. Use GIFs for anything that has text, for cartoons and for such things as drawings and maps.
   Whew! Why should it be so difficult?
   Because we're still babes in the digital woods, that's why. And because our software is incredibly dumb. It should make all these decisions for us. Until then, we need to know what works and what doesn't, and why.
   
   Let's forget Web pages for a minute. My original article pointed out that PNGs are better than JPEGs when you're storing or editing your digital images, period. I wasn't referring to Web pages or Web-page design.
   And that's what brought out the nitpickers from the TIFF brigade. TIFF (also called TIF and pronounced just like you'd expect it to be) is another image format. TIFF has a lot of fans, but unfortunately they're usually not around when you need them. That's because most TIFF users are professional graphic artists or photo editors, and they're not likely to be hanging around a digital water cooler chatting about images. They're making a living using TIFFs, and that means they're busy.
   There's a secondary problem with a lot of TIFFers. I've been harboring this for a couple of years so I'd better let it go: A lot of TIFF users are stuck-up Mac users who have no idea what is really going on outside their cubbyhole. Say anything about another image format to these folks and they just snort.
   To be fair to all seven Mac users in the world, TIFF is the default image format for professional and semi-professional image processing and editing. But Windows and Linux users who try to stray into the TIFF fold discover right away that they have to choose between a Mac version of a TIFF and a Windows version (or non-Mac version) of a TIFF. That's not just stupid; it's insulting, too. Windows and Linux users outnumber Mac users by about a billion to one, yet Mac users are still making life difficult for all the rest of us by sticking to an old method of doing TIFFs.
   (Technically, the byte order of Mac TIFFs is different from the order in non-Mac TIFFs. The processing chips in Macs have an upside-down byte order compared to the chips in PCs. Complicating this is the fact that what I just said is literally untrue; I was simplifying it, but it's too arcane to get into here. A further complication is the fact that PC chips are the guilty parties, because they're the ones with the backward byte order. PC chips (the Pentium family, for example) are so universal now that the backwardness almost seems right. (Right-minded people might consider this backwardness to be ssendrawkcab, however.)
   
   So we need to forgive Mac users and their backward TIFFs. As long as you recognize that the world has two different kinds of TIFFs, feel free to use TIFFs in your image storage and editing. If you're using a Windows PC and your brother-in-law has a Mac, you might find you can't share your non-Mac TIFFs with him; you'd have to open them and then save separate versions in Mac TIFF format. (Of course, you could simply use a format both Macs and Windows PCs share without difficulty, such as PNG.)
   If your image-editing program has TIFF as an option, it probably also lets you choose between compressed TIFF and non-compressed. The type of compression might also be selectable. LZW compression is common. It's lossless (the picture is not degraded in any way) but takes longer to save. If you have a fast PC, use LZW. Otherwise, skip compression.
   
   Other image formats you might need to know about:
   PSD (Photoshop Document), used by Adobe's image-editing software. It's lossless and ideal as an intermediate storage format while you are working on images in Photoshop and other Adobe software that uses PSD. Many other graphics programs can handle PSD images, but I don't recommend PSD for the final version of your image file. Use a universal format such as PNG instead, or do what many serious photographers do and save one copy in PSD format and another in TIFF or PNG.
   FIF (Fractal Image Format), used by an image-compression plugin (helper program) for Photoshop and for programs that can use Photoshop plugins (Photo-Brush, Paint Shop Pro, Corel Photo Paint and others). Stay away from fractal image compression unless you also save your images using standard, lossless formats. (In that case, why use fractal compression anyway?) Fractal compression will grow up someday. As of now, it has a limited usefulness for most of us.
   PICT (Picture), an old image format used only by Macintosh computers. It's too limited. Avoid it.
   TGA (Targa), an almost forgotten format invented by AT&T. Avoid it.
   PCX (Picture Exchange), a format useful in the early years of 16-color displays. Avoid it.