Ask the Experts: DPI Demystified
by Wendy Dunning, from the November 2012 issue of The Artist’s Magazine.
Q: Most juried art shows now require that entries be submitted electronically or on CDs. Entry instructions give detailed technical directions, but I don’t understand terms like dpi and pixel. What do these terms mean, and how do they relate to photographing my artwork? ~Griff Saunders, Boulder, CO
A. When you create a digital representation of your artwork, either by photographing it with a digital camera or scanning it, you’re using the camera or scanner to break down the image into little pieces. Imagine laying a fine grid over your image, then assigning a color to each block in the grid. Each block, called a pixel or picture element, would become an average of the colors within it—one value that a computer can store in its memory.
The number of pixels per inch (ppi), also called dots per inch (dpi), describes the resolution of the image. Now imagine a large grid with only a few blocks available to color your image. More colors would be averaged into one value, so your image would have less detail and might even look blocky or pixelated. It will be a low-resolution or lo-res image. Add more blocks per inch, and you’ll have a more detailed and crisper image. Add a sufficient number of blocks or pixels per inch, and you’ll have a high-resolution or hi-res image. Standard screen resolution is 72 dpi (which is considered lo-res), and standard print resolution is 300 dpi (which is considered hi-res). These resolutions are determined at 100 percent of the digital image size (not the size of your original artwork). In other words, for a painting of any size, if you have a digital image that’s 4×5 inches at 300 dpi, then the largest that image can be printed is 4×5 inches. If you try to print it larger, you’ll lose resolution.
How does this relate to photographing your work? First, you want to use a camera that has a high pixel count, something that captures images in at least the nine megapixel range (although cameras are coming out with higher megapixel ranges). A camera with a high pixel count will give you an image that will print at 300 dpi at 8½x11 inches. I recommend getting a single lens reflex camera (SLR) rather than a point-and-shoot style camera, and make sure you use a high-quality lens. Set your camera at the highest resolution available (SHQ: Super High Quality or HQ: High Quality), and if your camera has a RAW format (explained in the next Q&A), use that setting also.
The important thing to remember about resolution is that you can always save an image down to a lower resolution, but you can’t increase the resolution of an image because the computer can’t invent information that it doesn’t have. Again, think of this in terms of a grid: the computer can take four blocks and average them into a new single block to create a lower resolution image; however, to create a higher resolution image, the computer will just take a block and divide it into four blocks of the same color. It can’t invent four different colors after it’s averaged them together.
Always submit images for art shows or competitions according to the specifications given. Ignoring these may hinder a juror’s ability to view your images clearly.
Wendy Dunning is the design manager of the Fine Art Community of F+W Media, Cincinnati.
- Color systems: RGB and CMYK, online article by Wendy Dunning
- Digital file formats decoded: TIFF, EPS, PSD, and JPG, online article by Wendy Dunning
- Get the Most From Photoshop, book by Simon Joinson
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