Guidelines for printing a raster image of text?

Question

I need to include png images of text in a photo book, but I don't know how to achieve the best quality. Are there any general guidelines?

For example, should I use a DPI above 300 and let the printer handle any downscaling needed? Is output sharpening advised?

The book will be printed on matte photo paper by a photo lab, but I don't know what print process will be used.

Background: I'm using the photo lab's own software to design the book, as I don't have the software or knowledge to create a pdf where I could include vector text.

Note that I do understand the purpose of DPI, and that rasterised text is not ideal. My instinct is to increase the resolution of the text image at fixed physical dimensions, but I'm unsure if there are any hidden downsides to that (e.g. in supplying a higher DPI than the printer is capable of) or if anything else should also be done.

Answer 1

DPI is not a measure of image quality, or the resolution of a digital image. It's only the output resolution. The DPI setting is meaningless if you don't also know what size an image is to be printed.

Here's how to work out what size/quality an image for printing has to be.

1. Find out the physical size in inches that the page will be printed. Let's say for the sake of argument the page is 8 inches by 10 inches.

2. Take those dimensions, and multiply each by 300dpi. (note 300dpi is the usual output resolution for photo printing of small prints found in books etc. Ultimately should really check with your photo lab what they recommend).

So now we get 8"*300=2400px and 10"*300=3000px. So the text needs to be typed on a page which is 2400px x 3000px

3. Use MS Paint or any raster image editor (such as GIMP which is free). Using the size you worked out, create a new document that size.

4. Type the text. Save/Export the image in the format required.

That's it.

If you want to, I guess you could double up on the resolution of a raster image and assume output at 600dpi, and use that figure for the calculations. Obviously that will make a bigger image, but it will have more detail.

However, to be honest with you, rasterized text is not the best. It would be much better to create a booklet in desktop publishing software, and type the text, and export as PDF - this will keep the text as vector. If you want free software, you could try Scribus. I don't know what your computer skills are like, but there is a bit of a learning curve with software like Scribus.