Thursday, July 1, 2004

July/August 2004 HelpLine

DPMag Published in HelpLine

Or, once you've discovered the series of steps required to make corrections to an image, you could assemble all those steps into a script or action that could be run on each file during batch processing.

Most of the manufacturers listed above have trial versions you can download. Try them out to see if they will do what you're looking for.

Megapixels And DPI

Q)  Digital cameras use megapixels as their measure of resolution, but I can't find an explanation of how to equate megapixels to dpi. In other words, at 300 dpi, how big can you make an image from a 5-megapixel camera? It's said that a 5-megapixel camera takes sharp 11x17 pictures, but at what dpi?

Bob Daniels
Toledo, Ohio


A)  There really isn't a standard for referencing megapixels to dots per inch (dpi), or pixels per inch (ppi), for that matter. You can't judge the area of a town by counting how many houses it has. You need to know how far apart each house is from another. It's the same with pixels. Your camera's image sensor is jam-packed with photosites (the technology that receives the incoming light from your lens). These photosites are used to create the pixels that are stored on your memory card. They will give you a total number of pixels (5 megapixels, for example), but pixels or dots per inch can't be determined from a pixel count. You must know dimensions.

When you download the image into your computer, you're bringing in pixels, but you haven't decided how far apart each pixel is going to be from the next. That will depend on how you want to use the image. If you were to take those 5 million pixels and display them on a monitor at the usual 72 dpi to 96 dpi, you'll end up with such a large image that you'll display only a small portion of it.

Regarding your question about what will happen when you print the image, you can adjust either the image dimensions or the dpi for the original set of pixels that came from the camera. These two values are tied together like a seesaw. As the dpi goes up, the image dimensions go down, and as the image dimensions go up, the dpi goes down.

 

 


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