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?
Nice question, and it is deeper than you think. But let me be more specific about the units.
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.