There was supposed to be a small guide on how to prepare files for printing. This is in the end a very useful knowledge, and it is easy to make a mistake in this area. And mistakes in preparing for printing can be expensive. I thought, however, that first of all I would write a little bit about graphic formats, because at the end of the already prepared for printing file you have to save it in some format and give it to the printing house.
And it is worth knowing what is the difference between JPG and PNG, or what secrets are hidden in the PDF format. Yes, this entry is definitely addressed to beginners and curious and discusses graphic formats in terms of printing.
The most popular graphic format, which is JPG. Of course, this format stores raster graphics, not vector graphics. This format is JPEG and means Joint Photographic Experts Group, whatever that means. The genesis of this name and the dates connected with it will also be omitted.
Why? Because it’s not important. Much more important is the fact that a JPG file can store images in both RGB and CMYK colors (more about this here). As you know, we print in CMYK colors, so this makes it possible to send a JPG file to the printer with confidence.
Theoretically, just set the color mode to CMYK and you’re done. Theoretically, because what in practice is in the next entry. Besides, there is something worth remembering about – it is a loss compression algorithm, which causes the image stored in the JPG to lose its quality.
Files in JPG format can have a very small size and very poor quality. And a poorly-quality photo submitted for printing will of course cause that the printout will also be poor.
How does loss compression in JPG format work? In short, the compression algorithm assumes that the human eye is still unable to distinguish every pixel from each other. Therefore, it groups pixels into blocks and averages their colour values. The result is a smaller number of pixels of different colors, and as a result, the file contains less information and as a result its size is smaller.
Another raster graphics format. As the name suggests – Portable Network Graphics, a format designed for use on the network, not in print. Why? First of all because the PNG format does not support CMYK colours. That’s right – you can’t save an image in CMYK color mode to the PNG format. This file type saves images in RGB colors only.
Someone will ask – so why this format? as the name suggests, to the Internet. Images in this format are saved with lossless compression. So you can be sure that all Internet elements, like icons, graphs, logos, illustrations with little color and other graphic objects will look as they should – clean, without any artifacts.
This in turn means that the PNG format is not used to save pictures or large images that contain lots of colors. Such files simply reach a very large size, which disqualifies them for use on the Internet. So if you want to show an icon on the web – choose PNG, but if the photo – the choice will be JPG.
There is another thing that makes the PNG format so popular on the web. It is transparency. The PNG file actually contains colors in RGBA mode. So there are three standard channels – Red, Green, Blue and an additional, fourth channel – Alpha. The alpha channel allows you to achieve a total of 101 levels of transparency in the PNG image, from 0 to 100.
In the case of JPG, each transparent part of the image is converted to white, and here the transparency is retained. This is an important feature, not only on the Internet, but also in print, especially when printing on a coloured surface. Only that PNG, as I have already mentioned, is not suitable for printing. So what should be done?
Very flexible raster graphics format. In practice, TIF combines the graphic formats JPG, PNG and… PSD. Why? With JPG it takes support for RGB and CMYK colors, as well as the possibility of compression, which can be completely disabled here.
With PNG is taken the lack of lossy compression, so the image does not lose quality and transparency. That’s right – TIF format allows you to save the file in CMYK color mode with an additional alpha channel. Okay, what about PSD?
After all, it’s a working Photoshop file format… A TIF file can simply store the same information as a PSD file. So layers, groups, styles, paths, intelligent objects and everything else. And this is a great option when we want to move an image to another application, like CorelDraw, but we want to keep the whole file structure if necessary.
It also allows you to completely turn off compression (PNG). It also allows you to save information from Photoshop (PSD), and to reduce file size, it allows you to skip the entire layer construction and spit out a flattened image.
TIF file gives really good possibilities, it’s true. But the fact that it only supports raster graphics is impossible to pass. After all, when designing for printing, we get much more freedom when we work in vector graphics programs. Using PDF format we can store both vector and raster elements. And this is only a combination – raster graphics, RGB, CMYK, transparency, vectors, support for multiple sheets in the area of one document just everything.
The PDF format was developed for digital documents, but since 1991, the date of its creation, it has acquired many other possibilities, including those used in printing. Just as TIF preserves the construction of a Photoshop file and transfers the image between programs, PDF preserves the construction of the printed file and transfers it back to you.
Bleeds, colors, number of pages and all the rest will be preserved if we create the file in Illustrator and the printing house uses Corel. The problem begins when we use complex effects for objects in the project – shadows, grid gradients and others, which Corel does not support, and with Corel we want to edit these effects.
Therefore, it is safer to use such elements in raster graphics programs and use TIF files, which then need to be placed in a vector file.
To sum up, we can freely combine raster and vector elements, save the file in PDF format and be sure that everything in the printing house will be printed as it should be, regardless of the software used by the printing house.
PDF format has some “dangers”. I think danger is a good term. Many graphic designers for sure at least once met the situation where the client sent the logo in a PDF file, so theoretically it was supposed to be a vector, correct version, but inside it turned out to be a poor quality JPG. PDF allows to store different file formats, so you can save a raster file in it and pretend it’s vectors.