Shuki, did Nicolas give a more elaborate explanation than that they aren't the proper quality for professional printing. I think I know what he is aiming at, so I'll explain it a bit here.
I'll start with the regular bitmap images for some basic understanding. Vectors work different.
Pixels per inch (PPI)
For regular rasterized (bitmap) images you have a grid of pixels. Usually you have a certain amount of pixels per unit of distance, commonly Pixels Per Inch (PPI).
PPI is the resolution of an image, of a certain size, that is to be printed.
So let's assume we have a picture of 100 x 100 pixels that has a resolution of 100 PPI. If you would print it the result will be an image of 1 inch x 1 inch.
We could do now two things in changing this image regarding it's dimensions: Resize or Resample
- Resize: The amount of pixels will stay fixed. You cannot change these.
Example: if we adjust the PPI to let's say 200, the image dimensions will also change , i.e. we will have a 1/2 inch x 1/2 inch image.
- Resample: The amount of pixels is altered but your output print size will be the same.
Example: The printing size stays the same, so 1 inch x 1 inch. If we now change the PPI to 200 your picture of 100 x 100 pixels will be changed to 200 x 200 pixels.
So in short: Resizing -> Changes the output printing size, Resample -> Changes your picture.
Dots per inch
When a printer prints it drops drops of ink. Each drop can be considered as a "dot". Depending on your printer you have a certain DPI resolution. For example if you have 600 DPI, again with the picture 100 PPI and print it you will have 36 dots of inkt per pixel. (600 DPI x 600 DPI / 100 PPI x 100 PPI)
Now if you do the same with a 100 DPI printer with the picture of 100 PPI you will have 1 dot of inkt per pixel. This means you will have a less accurate color and thus a crappier print.
So that is it for bitmap/rasterized images.
Vectors images are composed of mathematical objects (lines, shapes etc). Because of this you can change their size and they will not give you those ugly big pixels if you scale up. But because of this vector images don't really have a resolution, i.e no real PPI. You can make them twice as big but they still looks as good.
So you would say Inkscape SVG's should work just fine, but I found some catches.
Inkscape
Ok now let's go to Inkscape. It's default setting is A4 and I think you might be using that to draw your diagrams in. The A4 dimensions in Inkscape are 744.09 x 1052.36 pixels. We want to print it on A4 paper which is 8.27 inch x 11.69 inch. So if we divide the pixels by the inches we get PPI and this will result in 90 PPI as a resolution for bitmaps. This resolution happens to be standard for Inkscape. If you choose to use the standard A4, letter etc, it always uses the 90 PPI resolution. This means if you import a 100x100 pixels, 180 PPI image it will be doubled in size in Inkscape (180/90=2). So you have a 200x200 pixels image. It's not that important for you because you use the vectors and not bitmap, but it is nice to know.
The second thing is the color support of Inkscape. Laptop screens and such use LED's consisting of RGB, i.e Red, Green and Blue to create the colors on your screen. Combine them and you get other colors (yellow, purple, orange for example) . Printers often use CMYK, a different set of colors (cyan, magenta, yellow, key=black). So there needs to be some sort of conversion with what you see and what you print.
When you print directly from Inkscape it flattens out the image and prints it in RGB. In other words color values change slightly. The same happens with exporting to a PDF in Inkscape. (see
here)
There is a workaround for this, at least if I must believe
this site I haven't really made this happen yet because I don't have the ICC-profile listed on the site. Maybe you can import your SVG in Scribus and get the needed professional quality. (I think I will be playing around with this later)
Well this was it. Just some information I searched around for and processed
.
Good luck with making your book!
Edit: On a sidenote, why does this forum always give me a heart attack when I make a long post and I get auto logged out
thank god for tabs and refreshing.