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Why So Many File Formats?

Files of many different types populate the world of digital photography. For starters, your camera can save in either jpeg or raw files. But there are countless more formats you could run into from time to time. Fear not. There is at least some method to the format madness.

We can divide the world of computer image formats into two broad categories, "raster" and "vector."

Photographers deal almost exclusively with files built from pixels (picture elements) that each record their part of the whole. Stacked into rows and columns, they create an image, one tiny spec at a time. Such files are known as raster images. The designation has aged somewhat, but "raster" refers to how an electron gun would render images in old-school TV sets and cathode ray tubes. When you think about it, it's kind of ironic. It used to require a CRT monitor to display digital images correctly. Today's LCD monitors have no raster lines, but the name once made more sense. Even as technology has moved on, we're stuck with the term.

But there is an entirely different approach to storing digital images. Instead of being comprised of discreet pixels, a vector file contains information on how to draw a picture. Vector file formats include lists of lines, circles, and graphic shapes built from other algebraic functions. Graphic artists often use vector formats for corporate logos and similar art. Examples of vector formats include EPS (Encapsulated PostScript), SVG (Scalable Vector Graphics), and DXF (AutoCAD's Drawing Exchange Format).

You might wonder why we can't all get along and use the same type of files, but raster and vector are suited to different purposes. Raster files excel at recording the nuances of color and tone one encounters in the real world. Vector images typically deal with fewer colors than raster. But by containing mathematical formula data, they can scale to any size without losing precision. You end up with stair-stepped "jaggies" if you enlarge a raster file too far.

I have graphic artists friends, but since this is a photography site, I will focus primarily on raster file formats here. I'll leave the discussion of why there are so many vector formats to users of Adobe Illustrator, AutoCAD, and the like.

Raster files come in quite a few variants, too. The earliest didn't even support color since the computers of that era couldn't. We've come a long way. But that progress has also produced much of the acknowledged file type confusion. File formats get agreed upon to solve a problem or improve some capability. Perhaps it's the limited bandwidth inherent in how computers connect to the internet. That was the case with the jpeg standard. The most straightforward format for pixel data is the BMP (bitmap). The rows and columns of RGB data come one after another, filling the file. But such files are large, and early dial-up modems were slow.

The first attempt to solve the impedance mismatch problem gave us GIF images (Graphics Interchange Format). GIF files sacrifice the precision of color for compactness. They work well for simple icons and web graphics but do a poor job of handling photographs. Still, it was better than nothing. Web pages everywhere sprouted an abundance of tiny stick-figure men and other ornaments, often for no apparent reason.

The jpeg file took advantage of improved computer CPU power to perform more sophisticated image compression than the simplistic GIF technique. Images displayed as jpegs could appear blotchy or blurry, an artifact of the lossy compression employed. But when not overdone, jpegs are perfectly adequate for most online uses.

With more computer power comes greater computer responsibility. The display of lossless images became possible with the wider availability of broadband and increasing CPU speeds. PNG (Portable Network Graphics) don't compress as well as jpeg, but they produce excellent results. PNG compression is lossless, so lines and edges appear crisp, and color gradations stay smooth and lifelike. PNG files also support greater bit depths for increased accuracy and transparency for better control over online layouts. PNG is ideal for critical work where the image's appearance is paramount. Where speed is your major concern, though, stick with jpeg.

Then there's TIFF (Tagged Image File Format). A type of file now reserved mainly for print production, TIFF saw greater use before the advent of PNG to overcome jpeg limitations. Web browsers can't natively display TIFF files. But TIFF provides a way to defer and minimize jpeg loss until the very end of the production process.

Because of its prevalence in the market, Adobe Photoshop's PSD file format has become a de facto standard, now also supported by many third-party applications. You can think of PSD as being an improved but proprietary TIFF substitute. If you use Photoshop, you will almost certainly want to use PSD. If your preferred image editor doesn't come from Adobe, your choices become more complicated.

The raw file format is more properly seen as an entire family of similar specifications, each unique to a particular camera brand. Even within a brand, raw formats are changing and evolving to support the defining features of new camera models. I'm unaware that Nikon has removed any capabilities from the NEF format unique to older camera models, but they seem to make tweaks for new ones often. You'll know when this happens to you when the software you've been using for years one day informs you it can't read the images shot by your new camera. While the details of jpeg, TIFF, and other raster formats remain essentially static, the inner workings of raw formats are in constant flux.

Today, we also have a family of formats for HDR (High Dynamic Range) imaging that let us go beyond the capabilities of more traditional raster formats. Swapping the standard whole-number integer encoding used by jpeg, TIFF, and the like for scientific notation floating-point numbers allows HDR files to record full-color detail over a vast gamut in terms of both hue and brightness. Transmitting and rendering HDR images require considerable power, though, so the adoption of HDR has been slow. I would expect it will become increasingly common in the years to come.

It isn't clear whether we'll see any of these formats fall by the wayside at some point. I expect, or at least not soon. Once a file type is used widely, it's hard to withdraw support. As much as we might want a simplified landscape of file formats, we don't want to give up any of the ones we currently have. Or at least enough people somewhere would get upset that it's unlikely to happen too precipitously. Right now, we have an abundance of types because each has a place where it works better than the alternatives.

The bottom line is simple. In the world of digital photography file formats, it takes all kinds. Or at least quite a few of them over the years.

So, vive la différence.

Date posted: July 10, 2022


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