In the color printing, ink of only 4 colors are used, which are cyan, magenta, yellow and key(black). When CMY “primaries” are combined at full strength, the resulting “secondary” mixtures are red, green, and blue. Mixing all three gives an imperfect black. And for each color, it has infinite shades and tones. (learn more here about the color basics, hues, tones, shades and tines).
The problem here is that how can we simulate the different shades, like pink color, of a color with the only the magenta color ?
In the 19th century, the graphic designers find that the discrete dots, varying either in size, in shaping or in space can used to generate a gradient like effect. And this reprographic technique is called halftone.
Check the picture below for a better and clear understanding:
Left: Halftone dots. Right: How the human eye would see this sort of arrangement from a sufficient distance.
With regard to the file formats for the printing of the paper printed box, the AI format is strongly recommended. If you don’t have an AI format, PDF format would work too. Below are some introductions to the common image formats for printing.
1. Native file format — acceptable print format for printers
When preparing pages for printing, the graphic designers generally use page layout programs to provide the structure and design for the job. Page layout files include the overall page design elements (rules, columns, screen tints, and so on) as well as text. These files, also known as native files, vary in format from one program to another and generally do not contain photo or illustration files. Instead, graphic files are linked to the page layout file. In addition, page layout files do not contain the fonts used to display and output the typefaces used in the document. Thus, jobs delivered by the designer to the printing company or other service provider in the native format must be accompanied by both the fonts and image files. Page layout programs provide a method to “collect” or “package” the supporting files that must accompany a native page layout file in order for that file to output properly.
Common Image Format
.psd is the native file format for the Adobe Photoshop, .ai for Illustrator, .indd for InDesign.
EPS (short for Encapsulated PostScript) is a vector format designed for printing to PostScript printers and imagesetters. It is considered the best choice of graphics format for high resolution printing of illustrations. EPS files are created and edited in illustration programs such as Adobe Illustrator or CorelDRAW.
Vector graphics are a scalable, resolution-independent format composed of individual objects or shapes. Vector images can be resized easily without loss of quality making them an ideal format for initial logo designs and illustrations to be used in multiple sizes.
2. Recommended file format (PDF)— stardard print format by SWOP
PDF/X1a is the most widely adopted, all-inclusive file format relevant to the printing industry based on the Adobe’s Acrobat PDF format. The printing layouts created in the Adobe Photoshop, Illustrator and InDesign all can be saved in the PDF format.
TIFF/IT-P1 is an internationally-accepted format accredited by the International Standards Organization and known as ISO 12639:2004. “ISO 12639:2004 specifies a media-independent means for prepress electronic data exchange using a tag image file format (TIFF). ISO 12639:2004 defines image file formats for encoding colour continuous-tone picture images, colour line-art images, high-resolution continuoustone images, monochrome continuous-tone picture images, binary picture images, binary line-art images, screened data, and images of composite final pages” (International Standards Organization, 2004).
PDF verse TIFF
Although SWOP allows designers to save files in either format, a review of the specifications pages for numerous publications reveals that the trend is toward PDF/X1a and away from TIFF/IT-P1.
3. Web image format (JPEGs, PNG, GIF) — the least wanted file format
JPG (short for Joint Photographic Experts Group, and pronounced jay-peg) is a file format best used for photo images which must be very small files, for example, for web sites or for email. JPG uses lossy compression (lossy meaning “with losses to quality”). Lossy means that some image quality is lost when the JPG data is compressed and saved, and this quality can never be recovered.
GIF (short for Graphics Interchange Format) is a file format for storing graphical images up to 256 colors. It uses a lossless compression method which makes for higher quality output.
PNG (short for Portable Network Graphics) was created as a more powerful alternative to the GIF file format. PNGs are not restricted to the 256 color limitation of GIF files and have better compression. A PNG file can be saved with a transparent background which allows you to place your image on top of another image without an outlining white box.
GIF files are probably the most popular on the web being used in logos and color images. Even though PNG files are widely supported, GIF is still the most popular.
TIFF, JPEGs and PSD
TIFFs, JPEGs and even PSDs are what you should be saving your bitmap files as (the sort of things created in Photoshop).
TIFFs and PSDs are lossless. You don’t lose any quality by saving a file as a TIFF or PSD.
JPEGs normally lose quality when you save them but take up a lot less space on your computer. A very high quality JPEG is often not a lot different to a TIFF or PSD, but it does very much depend on the sort of image you’re saving.
A TIFF or PSD is normally a better option than a JPEG. But if you’ve been supplied with a JPEG, from a camera or stock photo website, and you’re not modifying the image then you will gain nothing from saving it as a TIFF or PSD. A TIFF or PSD cannot create detail where there was none in the first place. But a JPEG can remove detail where once there was some.
There’s a couple of thing to notice in the pictures here related to JPEGs. Firstly, JPEGs can’t handle spot colours. So when this JPEG was saved it converted the Pantone colour into a CMYK value. Secondly, the white space in between the red lines on the JPEG is filled with a very subtle yellow/grey tint. This is due to the compression.
In the past decade, I’ve had a few hundred ‘just out of university’ graphic design interns through our door. Some with extremely portfolios of work, some with potential. Each time they have started, I have been astounded as to their almost ignorance of designing for print. They knew fundamentals of typography, white space, colour scheming, etc, however, they are ignorant about basic pre and post design stages.
We have created a list of the top 5 things that 80% of our new designers did not know when it comes to design for print.
1. True Black Color.
When you’re creating the artwork, and you pick black, even when working in CMYK, it reverts to almost black, (#000000 or 75/68/67/90 in CMYK) a default in the color picker. When this almost black goes to print, it comes out looking grey, which means unhappy clients.
Here’s the solution. Go to the color picker, and change the CMYK values to C50 M40 Y40 K100. True black for print, every time.
2. Bleed and Crops.
Bleed is the area of artwork that is extended beyond the actual dimensions of the document. It is used to avoid strips of white paper showing on the edges of your print. That is, a background colour or image should spread to cover the entire bleed area. The standard for the ‘bleed’, the edge around the document that will be trimmed, will be 3mm. This means that every side of your document needs an extra 3mm added on to it. If designing in Illustrator, this is easy peasy japanesey.
In the Illustrator, open a new document and you will see that there is a space for ‘bleed’. Make sure that this is set to 3mm for each the Top, Bottom, Left and Right, or that the link button is pressed.
Learn more here, http://blog.spoongraphics.co.uk/tutorials/designing-for-print-setting-up-crops-and-bleed
3. DPI and PPI.
PPI stands for pixels per inch. PPI is a measurement of image resolution that defines the size an image will print. An image that is 1600 by 1200 pixels at 300ppi will print at a size of 5.3 by 4 inches. Or it could be printed at 180 ppi for a printed size of 8.89 by 6.67 inches. The higher the ppi value, the better quality print you will get–but only up to a point. 300ppi is generally considered the point of diminishing returns when it comes to ink jet printing of digital photos.
DPI is better known as Pixels Per Inch, it is the measure of the resolution for printers. And it is often used interchangably with PPI, causing a lot of confusion, however, DPI refers to the resolution of a printing device.
When sending the artwork to print, you want to make sure that your dpi is set to 300. In Illustrator, this can be found on the New Document settings page.
4. PDF Formats.
Most printers will want you to send the final as vector PDF document. Using a JPG or PNG, will make it so that your text is fuzzy and your images less sharp. If you are using a combination of photos and art, then ensure that the photos were 300 dpi when you brought them in.
Printers have diferent requirements for formats (moo.com for example states in their preparing artwork section: ‘Make sure you pre-flight your PDFs using the ‘Adobe PDF/X-1a’ preset. This option can be found in Adobe Illustrator, Adobe InDesign and more recent versions of Adobe Photoshop.’) Make sure you ask your printer before sending the artwork what they prefer. Below you can see the selection for PDF/X-1a.
5. Exporting PDF With Marks & Bleeds.
Your art should have been started with the 3mm bleed on each edge. To make sure that all of the appropriate crop, and printers marks are on the final PDF here is what you do.
1. go to File > Save As, and make sure that PDF is selected in the bottom drop down box.
2. Name your file, and hit Save. This will bring up the PDF dialogue box.
3. On the left hand side, hit the tab for ‘Marks & Bleeds’ Make sure the boxes are ticked for ‘All Printers Marks’, and under Bleed, ‘Use Document Bleed Settings’ Hit Save PDF and you’re done.
Wah-lah! Now you should have an exported PDF that has all of the pretty printers marks like this one.