Image Export and DPI
We're often asked whether ImageExport will produce, say, 300dpi images.
The answer to that is yes. And no.
Strictly speaking, "300dpi" doesn't mean a lot when you're talking about images. It's a ratio between the number of dots in the image and the size of the image in inches. Without both pieces of information, dots and inches, it means nothing.
We can look at the image file in any image editor and determine the number of dots or pixels, but inches? Not really. A computer image is a collection of numbers that represent the colors of each image pixel. How big is a 12? Or a 17? Who knows.
But, and this is a biggie: some image formats (not all) can also include size and dpi information. And most programs will respect this information when you import a picture. So you can have the same image (same number of pixels, same file size) stored in two different TIFF files. One says "Make me 10 inches wide" and the other says "Make me 2 inches wide". Even though the image data is identical in every other respect, the images import at different sizes.
Image Export lets you create images with pretty much any number of pixels you need, but it doesn't set the "Make me this big ..." data in the files it exports.
A quick bit of math will get you the results you need, though. If you know you need to print an image at 10 inches wide and your printer gives the best results with 300dpi images, 300 dots per inch times 10 inches gives 3000 dots/pixels. Set Image Export to 3000 pixels and you're good to go.
The image may not import into your word processor or DTP program at 10 inches, but you know you've got the right number of pixels in the image to support the size you want to print it at. Just enlarge or shrink the image to final size and it will work nicely.
If you need to send the images on to a client who'll complain if they don't open or import at the expected size, you'll need to post-process the images in a program that allows you to set dpi/size without resampling the image. Photoshop or any capable image editing program can do this. Be sure to save in a format that supports dpi/size information. Not all image formats do. TIFF is a good choice.
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