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Bitmap Resolution

If you care about image quality, your Bitmap TIFFs should be at 1200 dpi (dots per inch).

Q: Why do bitmap TIFFs require a resolution of 1200 dpi?

A: Bitmap TIFFs are very different from CMYK or Grayscale TIFFs, which typically have an optimal print resolution between 300 and 355 dpi. These kinds of TIFFs contain color and value for every pixel that makes up the image. Bitmap TIFFs, on the other hand, are made up of pixels that are either black or white (no shades of gray). Therefore, these tiffs need more pixels per inch in order to appear sharp to the naked eye. Bitmap tiffs are excellent for solid black and white "line art" like text or simple logos. They will appear sharper than the same images in grayscale, as long as the dpi is set to 1200.

In the below example, we see a bitmap tiff at 1200 dpi and one at 600 dpi. The obvious choice is 1200 dpi for sharp solid b/w line art.

image

Q: OK, I understand that low resolution is bad. Can I just change my low resolution image in Photoshop to 1200 dpi by changing the number?

A: Not exactly. When you "change the number" from a low resolution to 1200 dpi, you are not really addressing the underlying problem. Doing this is called interpolation. Interpolation means that you are asking the computer to calculate the pixels that are not there. Computers cannot add new data to sharpen the image, it can only add pixels that "fill the gaps." What you end up with is a tiff that is at 1200 dpi, but not any sharper.

image

Q: OK. So how do I fix low resolution?

A: You need to re-scan your black and white image at 1200 dpi or start a new TIFF at 1200 dpi bitmap mode.

Note: When placing images into layout programs like QuarkXPress, PageMaker, or InDesign, be sure not to scale the image up or down much. A 1200 dpi image, for example, scaled up 200% will have a final resolution of 600 dpi! Low Resolution!

Also be sure not to overcompensate by making your image resolution too high. It is overkill to have images at 2500 dpi, for instance. It not only makes file sizes significantly larger, it also may create problems with final printing. Again, 1200 dpi is the optimal resolution for bitmap tiffs.

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