To understand the difference between dots per inch (dpi) and lines per inch (lpi), look at the way laser printers and printing presses create grey by using only black ink or toner.

To produce shades of black, any picture that has to be printed must first be broken up into a raster. Through this raster the black toner (or ink) can the distributed on the paper as dots of a varying size. The size of the black dot and the white paper around it create the impression of greys. Light areas have small dots and darker areas or shadows have larger dots. The image broken up by the raster is called a halftone, the raster is a halftone grid, divided into halftone cells.

The halftone grid is dependent on the fineness of dots the output device can produce. In other words, if you have a 300 dpi laser printer, your grid can only be produced using 300 dots per inch, which means that you are limited in the variance of your halftone dot, much more than with a 3600 dpi imagesetter.

This limitation means that the distribution of your halftone cells depends on your grid, if your cells are too close together, the grid will not allow the printer to vary the size of your halftone dot and you cannot produce enough shades of grey, the image becomes blotchy. The closeness of the rows of halftone cells is measured in lines per inch or the line screen.

In printing the number of lines per inch used depend on the dpi of the output device and also on the type of press used and the paper. A small instant print press cannot print dots as fine as a big, commercial printing press. Jobs printed on uncoated paper or newspaper typically require a coarse line screen (85lpi) because these papers absorb a lot of ink and the dots spread out (dot gain). High quality commercial printing is usually done on high quality coated paper, on which a much sharper dot can be produced (150-200lpi). The dots in coarse line screens can easily be seen by the naked eye whereas fine line screens look almost like a continuous tone.

While the above related to output, dpi and lpi are already very important when scanning your images. To reproduce with clarity at a certain line screen, a scan needs to have a certain resolution. A rule of thumb is to scan in at approx. twice the final line screen, e.g. a picture printed at a 150 lpi needs to be at a resolution of 300 dots (or pixels on screen) per inch.

The image will be broken up into a raster determined by the line screen. There needs to be enough information in the picture to support the line screen, superfluous information, e.g. more than 300 dpi at 150 lpi, will be discarded.

Another way of producing shades of black or a colour is by varying the number of very small dots on a page, as opposed to the size of the dot. This technique is used in most inkjet printers and produces very good, photo like results. It is called stochastic screening, or frequency modulation. It has the advantage of producing relatively good results, even when the image resolution is below 300 dpi.

Sending files to your printer has lost a lot of its complexity, the universal adoption of PDF, improved software applications and automated checks have made life in prepress a whole lot easier. There are still some errors, though, that persist even in PDFs, and that could ruin your print job. Here is our list of the top seven issues with files we receive:

1. Colour usage and control
2. Image quality (resolution and compression)
3. Fonts
4. Bleeds
5. Die lines - Varnishes – Embellishments
6. Missing files
7. Dummies

1. Colour usage: Files are not in CMYK when they should be, or they are when they should be in spot colours. Documents are created and then sent to us in RGB. Many files are converted without the right settings and the wrong colour profiles are embedded (The strawberries on the left were converted using an unsuitable profile making them lose contrast and look dull.) Then there are specific colour problems, like the make up of a rich black. Colour is still one of the most complex topics in print and talking about colour is necessary, though sometimes difficult, as colour perception is very subjective. If you want your printer to make your pictures look good, let them know, give them your original files and some time, if you want to do it yourself, ask them for colour settings and a press profile.

2. Image quality: Many pictures are used for online publishing and their resolution does not support print at bigger than postage stamp size. These pictures are often taken from an online environment, without supporting the quality requirements. Left in RGB, often with lossy compression (jpg), these images don't look good in print and make any publication look cheap. (The strawberries on the left were saved several times using jpg compression, making them lose definition and look pixelated.)

3. Fonts: Still way too complicated to handle, fonts can be an issue, even in a pdf workflow. They should be embedded when working with print files. All of them, always.

4. Bleeds: One of those things that a computer cannot catch is lack of bleed. You can easily check for it by looking at the edge of the page, but the number of times that our prepress has to extend a coloured area or stretch a picture is enormous.

5. Die lines - varnishes - other embellishments: They are the fun part, but they still need artwork to produce. They are often not set up correctly, often the knife line does not overprint (ie. leaves white line underneath); perforations are marked as dotted lines on the art, when there should really only be indicators instead of an actual printed line. Some of these can get a bit tricky, so the best thing might be to talk to your printer / prepress person and ask them, how these finishes should be indicated on the artwork. The worst thing to do is to send that urgent file away with none or unclear instructions and hope that "She'll be right".

6. It is not so easy to collect all relevant, i.e. final version files for a project. Sometimes it is just one pdf, but sometimes there are native files with fonts and pictures, sometimes there needs to be a database that is required for a variable data job. We need these files. Without them, we can't print (Yes, they could well be on your desktop).

7. Dummies are good, sometimes absoutely necessary. Once you have tried out, how many ways there are of folding an A4 to a DL (see our folding guide) you know why. For multi page publications we always run a laser dummy. For other jobs, especially those out of the ordinary, we love to have a folded dummy to understand, how you expect things to look in the end. Otherwise, someone will be guessing. And if it's that nightshift operator, who wants to get the job done, chances are that his idea of which one should be the back panel in a brochure might not be the same as your's.

 

A quick google shows that these are universal issues that will probably not go away any time soon. This makes it so important to talk to your printer and discuss what you want them to do.
Some customers want us to correct anything we see and suggest enhancements, for example to brighten up dull images. However, there are others that don't want us to touch anything and either run their file no matter what or alert them to fix problems. Either way, we need to know.

There is an almost unlimited number of ways paper can be folded. To communicate the way your brochure should be folded it is important to use accurate descriptions. Shown below are some of the most common folding methods.

Keep in mind that folding is a mechanical process that may vary slightly depending factors such as paper thickness.

Half Fold

Most common type of fold. Examples: A3 fold to A4 or A4 fold to A5.

Roll Fold

Panels fold in on each other. Each panel, from the outside in must be successively smaller to allow for the paper thickness.

Gate Fold

Two end panels fold inward, then folds again vertically down center of page.

Parallel Fold

This type of fold requires the finished piece to be folded in half, then in half again – final, folded size is one quarter the original width by the same height.

3 Panel Fold

A common layout is the three-panel, two fold brochure on A4 size paper that folds down to fit into an envelope. Example: A4 fold to DL.

Concertina or Z Fold

Panels fold on top of each other like an accordion. Called a Z fold when there are 3 panels. The resulting brochure can be unfolded and laid flat to be read from side to side.

 

At SOS we have extensive bindery equipment which allows us to finish most multi-page publications in house. You can choose between the following forms of binding:

Padding:

Glue is applied to one or several edges of the sheets, holding them together. Most suitable for notepads and other items where single sheets need to be torn off without affecting the sheets left. - Cost: low | Durability: low

 

 

Side-stapling

Staples can be applied at the side or at the top corner of the sheets. As this can be done inline on our laser printers, this is a very cost effective and fast way of holding together items like handouts.

Cost: low | Durability: medium

 

Plastikoil binding

A spiral plastic cord is threaded through holes that were punched at the long or short edge of the sheets.

Cost: medium | Durability: high

 

 

Wiro Binding

A metal wire is clamped into holes that were punched at the long or short edge of the sheets.

Cost: medium | Durability: high

 

 

3-, 4-, or 5-Ring Binding

Ring binders are popular were sheets have to be able to be taken out or replaced from a publication. Most popular with training companies.

Cost: high | Durability: medium

 

 

Saddle Stitching

A fast way of binding booklets with up to approx. 80 pages, it is used in publications such as Time Magazine. Sheets are folded, collated and then stitched along the spine by 2 metal staples.

Cost: low | Durability: medium

 

 

Perfect Binding

Single Pages are collated into book blocks, hot melt glue is applied along the spine and a soft cover is drawn on, which is usually thicker than the text.

Cost: medium | Durability: medium

 

Burst Binding

Similar to perfect binding but more durable because sheets are folded into sections and punched along the spine before collating, to allow the glue to penetrate further into the book block. 

Cost: medium | Durability: high

 

Section Sewing

Similar to Perfect & Burst binding; it is the most durable; folded sections are collated into book blocks then sewn together with thread before gluing and drawing on a soft cover.

Cost: high | Durability: high

PUR Binding

Similar to perfect binding but using a more durable glue. This glue is extremely strong. It requires 24 hours drying time and it is much more expensive than normal glue. PUR binding is replacing section sewing as a high quality binding option.

Cost: high | Durability: high

If you want to get a document printed that uses screen shots, you can use separate software to capture images on your monitor, but in the end a screen shot will only be made of what’s on the screen, so the built-in facility of the operating system is normally enough.

The three factors that make (or ruin) screen shot reproduction are resolution, colour conversion and file format (compression).

• The resolution of the screen on which you take the shot is important, the higher the better. If you capture a 1680 x 1050 screen you will get a 5 MB RGB (6.8MB in CMYK) file which even at 300 dpi is definitely good enough for a reproduction at a size of 14 x 9 cm. Even larger sizes (up to A4) are usually fine.
• The colour of the screen shot is obviously RGB, so as with any image you need to take care when converting to not lose the vibrancy. colour profile for high quality sheetfed offset will get much better results than the Photoshop default of North American Standard Web Offset.
• Finally you need to be careful not to use any lossy compression, which would cause artefacts and blur the image. JPEG compression is such a compression method, you lose quality every time you save. I find that for screen shots tiff files with lzw compression works best.

So capture an image at the highest possible resolution, maintain the colour vibrancy and don't use lossy compression when saving the image, or the complete (pdf-) document.