I came across the following question: If I print text that was rasterized with a certain amount of dpi, how much dpi would be necessary such that the printed rasterized text would be indistinguishable from printed vector text? Is this even possible? I assume the answer depends on the font size and on what printer is used?
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1Here's a head scratcher... everything printed is raster. Everything. There's no such thing as a vector print. It all travels through a Raster Image Processor (RIP) which rasterizes everything vector or otherwise.– ScottAug 6, 2021 at 5:26
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2 Answers
Nice question, and it is deeper than you think. But let me be more specific about the units.
Simple answer
The resolution in PPI should be the same as the printer's DPI. Yes, they are different units. One is for the image, the other is for the printer.
But the trick is that the file should be 1 bit.
A More complex answer
When you have a grayscale image (for example 8bits), and not a 1-bit one now you need to use the dots of the printer to simulate gray tones. So the pixels can be bigger. This is proportional to the gray levels you expect.
Here is an image in Spanish but where you can see the correlation between the 3 units. PPI LPI and DPI.
I am simulating one printer with
- 1200 DPI and expecting only 64 (8x8) levels of gray.
- So the LPI I would get is 150 LPI
- And assuming I would use a 0° screening (which is not correct, only for explanation purposes) I would need a file of 150PPI
One typical resolution for plates for commercial print can have 2400 dpi or more.
Normally these dots are used to output grays for 8-bit images or 256 levels of gray.
To achieve this you can have a grid of 16x16 (16x16=256) so that 2400 DPI are now divided by 16 = 150. This 150 is a new unit called LPI.
A higher-quality print can have 3200 DPI or 200 LPI (3200/200=16)
This process is rasterization done by the prepress where your grayscale image is transformed into a 1-bit image done by the RIP.
(The conversion are not exact, because we normally rotate the angles depending on the color. Using a 0° is to simplify the transformations)
One different approach can be if we can really see the difference. Probably we can go with less resolution, for example, 1200 DPI-PPI 1 bit. on a High-quality printer.
But on a normal office laser printer, where the maximum resolution is around 600PPI the 1-bit image can be just 600PPI 1 bit.
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But you can not match it because the printee driver is abstracted. The font still matches the actual printers native dot grid better due to smarter engine. But by all means if one wants to act as a RIP processor it is possible.– joojaaMar 9, 2021 at 4:59
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2This jibes pretty well with the basic rule of thumb back when I first learned some of the basics (read: shop class), we still had optical equipment for typesetting but also some low-budget computerized equipment as well, and we pasted up things from various output sources to make the plates. When talking about resolution the "rule" was: line art 1200-2400dpi; B&W photo 600dpi; color (in theory, we only really went 2-color) 300dpi. I recall 600 being low for fonts when emitting stuff for paste up when compared to getting linotronic output from a real shop.– YorikMar 9, 2021 at 22:19
It would only depend on the resolution of the printer, not the font size.
Prints are always rasterized, even when using computer to plate technology (CTP), such as that used for offset lithography. In such cases you're probably looking at print resolutions of about 4,800dpi more or less. For home or office laser/inkjet printers that's likely much lower, say around 1200dpi or perhaps less.
Also as @Rafael has already said, needs to be a 1bit image.
answered Aug 6, 2021 at 12:55
