Pixel Perplexities and Other Digital Nonsense
by Michael Furtman
It is one thing for the average consumer to continually interchange the terms DPI (Dots Per Inch) and PPI (Pixels Per Inch), but for those of us in the business, especially editors, it is inexcusable. Yet in recent issues of OU, I’ve seen editors in the Ask the Editors section, and in the Markets section, misuse these terms.
Let’s get it straight. DPI is what your printer spews out – dots on paper. PPI is what digital cameras and scanned p_w_picpaths produce. True, the world won’t end if we interchange these terms, but we need to understand that PPI is input; DPI is printer output.
There seems to be a lot of confusion about digital terminology. For instance, editors continually say they’ll only take digital p_w_picpaths of 300 dpi. Well, first, it should be ppi, but beyond that, saying you want 300 ppi p_w_picpaths is like saying you want eight feet of lumber. What dimensions??? A two-by-four? Two-by-six? A sheet of plywood?
Requesting 300 ppi p_w_picpaths, without specifying dimensions, is confusing. Any digital p_w_picpath – ANY – is capable of being reproduced at 300 ppi. The outputted size will vary depending upon how many pixels the camera records, but even p_w_picpaths taken by your cell phone camera can be output at 300 ppi – they’ll just be tiny. It would be far more helpful to photographers if editors requested p_w_picpaths at a particular output size. Why?
The more pixels you have in an p_w_picpath the smoother the p_w_picpath will appear AT A PARTICULAR SIZE. For instance, the same scene shot with a 3 megapixel camera, and with an 8 megapixel camera, printed at a small size (say 3 x 5 inches) will look equally sharp. But that p_w_picpath won’t reproduce well at 11 x 14 from the 3 mp camera, but will look great from the 8 mp camera. This is called resolution.
Resolution refers to the density of pixels in an p_w_picpath. It is a measurement of height x width at a certain pixel density (ppi). But digital p_w_picpaths have no real absolute size or resolution – only a certain number of pixels in each dimension. Change the PHYSICAL size of the outputted print, and the resolution changes.
Think of resolution (pixel density or PPI) as coffee. In a cup three inches across, the liquid is dense and the color dark and rich (pixels packed densely). Spilled on a table, it spreads out thinly and no longer looks good (your “low resolution” output). At points in-between, the coffee is still dense enough to look brown and rich – still a usable p_w_picpath, depending upon the size.
I’ve sold p_w_picpaths taken from a 3 megapixel digital camera, and they look great, but only if printed a quarter to half page. If what the editors are saying is that they want p_w_picpaths that will hold up across a two page spread, then they need to say so.
And where did 300 ppi come from? Who knows. People toss that number around as if it were always the ideal output setting. The fact is that in the type of printing magazines use – off-set printing – resolution is determined by the number of Lines Per Inch (LPI). PPI for offset printing should be 1.5 to 2 times the print press’s LPI. Glossy magazines are typically printed at 175 LPI, so your p_w_picpath of at least 263 PPI (175 x 1.5 = 263) are often usable.
Some other crazy things editorial requests contain are misunderstandings about file types. In a recent issue of OU, one editor requested both “low-res” and “hi-res” p_w_picpaths in RAW format. Sorry. Can’t do. You CAN send the original “hi-res” RAW p_w_picpath, but there is no such thing as a low-res version. By its very definition, RAW p_w_picpaths are unprocessed p_w_picpaths. The resolution can only be changed by converting it to another file format, such as a TIFF or JPEG file.
And some editors say they’ll take only TIFF files, but not JPEG. Ummm…OK, I’ll resave my JPEG p_w_picpaths as a TIFF file if you really want me to, but the whole idea that JPEG is inferior to TIFF is just plain silly. I’m not going to get into the debate here about whether to shoot in RAW or JPEG mode, but it should be understood that a TIFF file made from an p_w_picpath shot as a JPEG will contain NO MORE INFORMATION, or look any better, than the JPEG. Take a 2 megabyte JPEG p_w_picpath, save it as a TIFF, and it decompresses to a full 18 megabyte file.
Perhaps these editors specify TIFFs because they’ve heard the JPEG myths: that the p_w_picpath is inferior, and that it continues to degrade each time it is opened and closed.
While the first “disadvantage” (JPEG compression is “lossy”) is true, I’ve printed many p_w_picpaths from both the JPEG and from the RAW file, and can tell no difference. The data lost is apparently irrelevant to the final product. And if the human eye can’t see it (which is what we’re ultimately shooting for), then do we really need it?
Second, simply opening or displaying a JPEG p_w_picpath does not harm the p_w_picpath in any way. Saving a JPEG repeatedly during the same editing session (without ever closing the p_w_picpath) will not accumulate a loss in quality. As I wrote recently in a Tech-E-Letter, I saved one p_w_picpath 30 times during an editing session, created a 100% crop of a detail area, and sent it and the original to several magazine photo editors for evaluation. None could tell the difference.
Finally, one editor in OU recently wrote that their publication doesn’t use “Photoshopped” p_w_picpaths. Oh really? I can guarantee, before those p_w_picpaths hit print, they have been sharpened, and checked for brightness, hue and contrast. That is “Photoshopping.”
Perhaps what the editor meant was that they don’t use composite p_w_picpaths, or what is called “photo illustration.” But editing a photo in a computer doesn’t mean changing it’s subject. It doesn’t mean adding a bird where there never was one. Editing is almost always as simple as just adjusting the saturation, contrast, or sharpness.
Digital imaging is here to stay. The learning curve has been steep for some of us. But it is time that we, as professional communicators, photographers, and editors, start understanding and using the correct terminology.
I’d suggest to anyone who would like to learn more about these just Google your questions. Type “JPEG myths”, or “understanding resolution” into the query bar, and you’ll find all the information you can handle.
This article was originally published in Outdoors Unlimited, the monthly newsletter of the Outdoor Writers Association of America. Copyright Michael Furtman, 2005.
