01 Introduction

 


 

01 Introduction. Basic grounding and terminology.

This tutorial is just to cover basic ideas you might need before jumping into the full tutorials. Grounding and concepts.

We have to start somewhere. We need some rules in place just so we can start bending them. These are the starting points:

  • All scanning is done in greyscale. Colour is no use, we only want black ink on a white background.
  • Scanning is done at a minimum of 400dpi. Ideally, at 600dpi. The higher the better.
  • We want our finished PDF plans to be small in filesize, let's say under 800KB. But we also want good print quality.
  • We want at least 300dpi output.
  • We get good quality prints at a small filesize by posterizing plans to just 2 levels, black and white, with no greyscale in between. Harsh and jaggy. Now I know this sounds like rubbish - but trust me, if your final print is at 300 or 400 dpi, the jaggyness is so tiny that it looks smooth to the eye.

 

Source > Photoshop > PDF

The source plan might be in any format. It might be a JPG, TIFF, PDF, DWG, BMP, PNG, whatever - we don't care. All we care about is: can we we get it into Photoshop? Once we have it in Photoshop, the absolute first thing we always do is convert to greyscale. Then in Photoshop we get to work and do the clever stuff - working all the time in greyscale mode. Then finally we posterize to 2 levels, and export to PDF as a full size plan.

 

Bitmap images and Vector images. What's the difference?

Images are either bitmap or vector.

Bitmap images are defined by pixels. They are made up of many pixels which can, each one, be one of many colours. Digital cameras create bitmaps. Scanning an image from a magazine creates a bitmap. Resizing a bitmap (upwards) will always lose quality. Blow it up enough, and it looks blocky. Editing of bitmaps is done through changing each pixel's colour/brightness etc. The file size of bitmaps can be very large.

Vector images are defined by maths, not pixels. A vector image is a collection of lines, nodes and curves, each one defined by a mathematical description. Every aspect of a vector object is defined by maths including the node position, node location, line length, colour, etc. Vector images are object-oriented while raster images are pixel oriented. When a drawing program re-sizes a vector image upwards, it just multiplies the mathematical description of the object by a scaling factor. So vector images scale up without any loss of image quality. Unlike raster images, quality is not limited by dpi. Vector graphics are used a lot for clip art. The file size of a vector graphic is often very small.

Photoshop is a bitmap editor.

 

Bitmap Image Modes:

There are many modes, but the only 3 we care about are these: Colour, Greyscale and Posterized.
By 'Posterized' I mean here, to be exact, 'Posterized to 2 levels'.
Here is what those 3 modes look like when we compare them, close up:

Colour
Pixels can be any one of millions of colours:

 

Greyscale
Pixels can be one of many shades of grey:

 

Posterized to 2 levels
Pixels can only be either black or white:

 
   
...or in extreme close-up:  
     

Why do we care about these 3 modes? Here's why:

Colour
This is what we don't ever want. Colour images use massive amounts of space and memory - much, much more than greyscale. Colour is wasteful, and whenever we see colour, we want to get rid of it, and fast. Processing images in colour takes more time. Storing images in colour uses up more space. Sending colour images as email attachments takes longer. Printing images in colour wastes ink.

Greyscale
This is where we get to work. It's where we do our processing - our editing and measuring, our stitching and cleaning, our adjusting and resizing. Greyscale is the workplace - it's where we get everything done.

Posterized
Once all the work is done, this is how we package things for delivery. This is how we send it out into the world. Posterized plans take up less filesize. They give better, sharper printouts. Posterized is how we deliver the goods.

 

Combining PDF documents into a single multi-page PDF - Pdfsam

We combine pages using Pdfsam - http://www.pdfsam.org/ - a free open source tool to split and merge pdfs. It's free and it does the job simply. Just deal with each page as a separate job, save each one, then finally use Pdfsam to combine all finished pages.

 

Ok, that's it, we're done. Now go read Tutorial2 where it gets better, we talk less and do more.