What is digital printing?
"Digital printing" refers to printing from a digital-based image directly to a variety of media. It usually refers to professional printing where small-run jobs from desktop publishing and other digital sources are printed using large-format and/or high-volume laser or inkjet printers. Digital printing has a higher cost per item than more traditional offset printing methods, but it avoids the cost of all the technical steps required to make printing plates. It also allows for on-demand printing, short turnaround time, and even a modification of the image used for each impression. (Source: https://en.wikipedia.org/wiki/Digital_printing)
There are two basic types of printing – Analogue and Digital. What’s the difference between the two and how do you choose? In the case of analogue printing, images are reproduced from a master image like a photo from a negative, or a print from a silk screen or litho plates.
The big thing is that with analogue printing you reproduce one image in one size only and the number of colours you use affects the price because colour separations have to be made. These separate colour images then have to be transferred to screens/plates and once ready for production, each colour has to be printed separately. As the cost of the colour separations (or set-up costs) are split over the number of prints, it is expensive to print one copy but cheap to print a large volume. Remember, there is a limitation that you can only print one image in one size and, generally, Litho prints go no bigger than an A2 (594mm x 420mm).
On the other hand, with digital printing your master image, which is usually digital (consisting of pixels) is converted to dots and sent directly from a computer to a printer. You can output various sizes and images and the printing cost remains the same per area you print. This makes digital printing much cheaper and quicker than analogue printing and is perfect if you want quick, personalised or lower volume printing:
- As digital printers do not require plates or screens (the prints are always full colour), there are no material set-up costs.
- Because you do not have to prepare plates or screens, printing can start much quicker.
- Digital printing is ideal for personalisation (or variable data) because variations in design like having different dates & venues on the same poster design, do not contribute to extra printing costs (no additional plates needed).
So go digital for low volume (say 10 posters) or where you need to print 1 000 stickers which contain differences (for instance different sell-by dates for different products) but not if you want 5 000 identical prints. If you want to brand 20 t-shirts and 100 golf balls for your team and maybe throw in a banner or poster, digital printing is the way to go and we can help you with all of it by using either our large format, direct to garment or UV printers.
How do I get the best digital print using my own art work or picture?
If you send us an image from your cell or something that you got through a Google Search, chances are that it will not print properly. You must remember that the image will not be printed exactly as you see it on your screen. There are many reasons for this but the two main reasons are that images on your screen are displayed between 72 and 96 PPI (pixels per inch) and are made up of RGB. Printed images on the other hand are made up of CMYK and must be around 300 DPI (dots per inch) to print properly.
Why do the colours of the finished product look different than it did on my screen at home/office?
No device in the modern digital workflow can reproduce the full range of colours visible to the human eye. Every device operates within a specific colour space that can produce a range of colours that represent a subset of the whole spectrum. For example, monitors will operate within an RGB – red, green and blue – colour range, while most printers operate within a CMYK – cyan, magenta, yellow and key (black) – colour range.
Not all device colour ranges cover the same subset of colours and therein lies the issue. Devices such as scanners or digital cameras will operate in different RGB colour ranges to printers, while not all monitors produce colours matching an identical colour range. This means that the exact same image, viewed on different monitors may be seem to have a different tone or colour range.
However, the problems don’t end there. The preview and output images of a single design process may also be considerably different. For example, a beautiful bright red screen colour could print as a faded orange. The only way to avoid this, is to use professional calibration and colour management systems when designing the art work. (Source: www.digitalartsonline.co.uk)
RGB & CMYK explained
As you know, colour is made up of different wavelengths. We see a piece of paper as white because it reflects all of the light and we see a piece of coal as black because it absorbs all the light. Orange objects reflect orange light and so on. You might think this is obvious, but we would like to explain its significance to having digital images that you see on your screen, printed onto something.
If you use light to mix colours – like your computer monitor – they are mixed using Red Green and Blue light (RGB). Because light is emitted, these colours are additive. You will see white because 100% Red, 100% Green and 100% Blue is emitted.
When printing you do not have a light source so you work on the principle of light being absorbed or reflected from the print media and a different model is used – CMYK (Cyan, Magenta, Yellow and Key, which is Black). Here you see black because the black ink that is printed absorbs all the light or you see white because no ink is printed on a white surface.
Why should it matter if you print an RGB image on a CMYK printer?
If you take a look at the diagrams above you can clearly see that the two models mix colours differently. For most of us it is not really going to matter because black is black. BUT... if you are very particular about the colour that you want to have printed, be sure to give us a CMYK file (which will on your screen will be displayed in RGB and look a bit different from the colours that will be printed in CMYK …).
It sounds like we are going around in circles but what we do want you to please remember is that images displayed on a monitor are in RGB. They are bright / luminous whereas printed images are in CMYK and are not luminous. An exact match to what you see on your monitor cannot be achieved, not even between two different monitors.
The eventual printed colour will also vary a bit depending on what substrate you print onto:
- the same image printed on glossy substrates will appear more vibrant than on canvas or on a t-shirt
- different substrates react differently to the same inks
- different inks (from different printers) react differently to the same substrate.
- There will always be minor colour differences.
How do I prepare the print file?
There are two kinds of files: vector files - that you can enlarge without losing resolution - and raster files which cannot be enlarged beyond a certain point without affecting the resolution. The main difference between the two is pixels, or picture elements. A pixel is the smallest physical element of a digital image and together millions make up the photo you have taken.
A vector file has no pixels and is made up of paths or lines defined by start and end points with curves and angles that you can edit individually. A path can be a line, a square, a triangle, or a curvy shape and are be used to create drawings. Because vector-based images are not made up of a specific number of pixels in a grid, they can be scaled to a larger size and not lose any image quality.
Raster or image files consist of a rectangular grid of pixels. These pixels define the graphic by giving individual points of colour and make up a picture. As the number of pixels per area is set when a file is created it cannot be enlarged too much without distorting. Megapixels describe the size of a photo, for instance a 10 megapixel photo is usually 3872 pixels wide by 2592 pixels high (3872 x 2592 = 10 million pixels).
There is a direct relationship between an image’s resolution and its PPI (pixels per inch): the higher the PPI, the more pixels and the more detail. However, there is no direct relationship between a photo’s megapixels and its eventual file size. The latter depends on what file format the photo will be saved in and what kind of file compression is used (the “quality” settings). It is basically a trade-off between file size and quality and several image compression algorithms have been developed to reduce the raster file sizes and JPEG, BMP, TIFF, GIF and PNG are the most common.
When a file is compressed, pixels that do not affect the display of the image are chucked away and you loose some resolution but it is okay. If you compress it too much, the photo will still display okay on your screen but the print won’t look good: If you increase the size of your image, the pixels will also increase and the bigger image could start looking jagged (pixelated).
So it is important to determine whether a picture is going to pixelate or not when you want to print it in a certain dimension. You must compare its digital resolution (PPI) to the required printing resolution (DPI).
Why worry about PPI (pixels per inch) and DPI (dots per inch)?
To prepare your image for printing, the image's pixels are converted into patterns of dots as illustrated below:
Although we all refer to monitors having a DPI, they really have a PPI that determines how big an image can be displayed without distorting. Think of this as your input resolution. DPI on the other hand is a printing term and indicates of how big an image can be printed without losing quality - it measures the density of dots printed (and not pixels displayed) per inch. Think of this as your output resolution.
Let’s get back to our example 10 megapixel photo. If it is displayed on a PC monitor which has resolution of 72 PPI then, at full size (meaning every pixel in the photo uses a pixel on the screen), it would be about 54 inches across (3872/72 = 54 inches). On a Mac, which has a higher resolution of 96 PPI, it will be reduced to 40 inches.
When you want to print the image, its RIP (raster image processing) software converts the pixels to dots. Printers can print many dots to make up a single pixel. These dots have spaces between them and this results in 300 pixels becoming 150 dots and spaces. So 300 PPI becomes roughly 150 DPI. This is acceptable for printing photographic quality images. When you move the viewer further away from the printed material, lower dpi is acceptable. A huge billboard might be printed at only 40 DPI but no one notices because everyone is far away from it.
Large format printers are classified by the number of dots that they can print per inch – the more dots the higher the resolution and the crisper the image. The printers can also vary the size of the dots being printed to better blend colour. If a printer is 1440dpi it means it can squeeze just over 2 million dots into a square inch. All of this compensates to trick the eye as long as there were enough pixels to start with.
Although we will let you know if there are issues with size and if the image might pixelate (resolution issues), it is your responsibility to ensure that the correct colour profile is given to us.