Welcome back! This week I will continue with the 2nd part of the previous post. Now, we are going to study all about printing resolution. Let’s go!
But first, let’s remember the key points:
- Digital images are formed by pixels.
- Image resolution relations the amount of pixels with length units.
- Its measurement unit is pixels per inch – PPI.
- Image resolution depends on the output device: screen or printing.
- Screens traduce pixels into “light points”. Each pixel of an image at 100% size will be produced by 1 “light point” or screen pixel.
- Screen’s PPI are fixed. It’s a physical limitation.
As we know, screens use “light points” to reproduce pixels. In fact, they have a fixed density of pixels. This means that if we have a low resolution screen, this will be its physical limitation, regardless of the image’s PPI.
In the case of printers, they use ink dots to create printed images. However, the relation between 1 ink dot and 1 pixel is not direct- as it happens with the screen at 100%. This means that 1 dot is not equal to 1 pixel.
Printing resolution depends on how many dots can be produced by the printer in 1 inch. In other words, DPI – dots per inch – is the number of points that are created in 1 inch length.
Lots of programs and manufacturers tend to use these terms indistinctly. Then, it’s quite normal to be confused. That’s why I am here to help you! 🙂
Printers usually mix CMYK ink in order to create the points that form an image. The size of these points has technical and physical limits. Then, each printer will have its own maximum DPI.
Then, we are talking about the capacity of the printer to produce a higher or lower resolution. If it can produce more DPI, the printed images will be sharper, having more details. It happens the same with screens, if you have more light points per inch, you will get better quality. Let’s review:
- Size in pixels: number of horizontal and vertical pixels of a digital image. It is the basic unit and it is a non-dimensional magnitude.
- Image resolution: relation between size in pixels and physical length.
- Screen resolution: number of light points that exist in 1 inch length. It’s a physical measure and it depends on each screen.
- Printing resolution: number of points that are produced by a printer in 1 inch length. It‘s a physical measure and it depends on each printer.
Then, the output resolution of an image is the information that our computer sends to the printer in PPI. However, the printer reads this info and reproduces it using its own method. This is, using DPI. As it seems logic, you will need that your PPI< DPI.
In screens, each light point doesn’t have a standardized physical size. It happens the same with printers since they don’t have a specific dot size. Consequently, each manufacturer can produce more or less DPI depending on the size of each point.
DPI is a technical feature of each printer, so we cannot modify it. It happens the same with the PPI of our screen. Then,… why do we need image resolution?
Resolution & PHYSICAL SIZE
A digital image contents the following info: horizontal pixels, vertical pixels, resolution in PPP. Then, let’s calculate its real dimensions:
- 5800 px / 72ppp= 80,55” -> 204,61 cm (remember that 1 inch=2,54cm)
- 3500 px / 72ppp= 48, 61” -> 123,47 cm.
Photoshop allows us to modify these parameters. Nowadays, there are lots of recommended PPP values that we can use depending on the quality that we need. One of the most used is 300PPP. Then:
- 5800 px / 300ppp= 19,33” -> 49,11 cm (remember that 1 inch=2,54cm)
- 3500 px / 300ppp= 11, 66” -> 29,63 cm.
As you see, physical size changes automatically when we change resolution. Pixels are just pixels! You simply decide how you want to fit them in 1 inch. This means that, if you have a high PPP, you will get:
- Better image quality. (Depending on technical, physical & visual limits.)
- Smaller physical size of the printed image.
Then, should you use always 300PPP? NO. It is a value that we use for small and good quality print outs, as a book or something similar that you are going to read in your hands.
If you want to print a billboard you will need much less ppp since you are going to see it from far away. So, you can just dive on the internet, follow the advice of printing professionals or simply rely on your own experience.
ENLARGEMENT & REDUCTION
As you know, all this means that if we want to print large size images with a high PPP we will need a big amount of pixels in our image. So, if our photo has a small quantity of pixels and we want to print it in large size, we will need to lower the ppp or viceversa.
However, we can increase the number of pixels of our image with an “artificial” process called interpolation. The software will create new pixels taking information from the existing ones in order to fulfill more space with them.
It happens the opposite when you reduce the number of pixels of an image. The software merges/combines pixels in order to make it smaller. This means a loss of information. These methods are not recommended since you will lose quality in both of them. However, they can be useful in some cases.
The file size depends on the amount of pixels – among others. So, it doesn’t matter the resolution. The previous example 5.800×3.500 px will be the same size in MB as long as they keep this amount of pixels. It doesn’t matter if its resolution is 72ppp, 300pp or 1000ppp.
FINAL KEY POINTS:
- Visualizing content on screen: if your image is big in pixels, it will be big in your screen. If you zoom in or zoom out, it will lose quality.
- Printing content: you need to know the physical size and quality that you want in your printing format. Also, it would help to know the distance of visualization.
That’s all! Thank’s for reading! See you next week! 🙂