Pythonneries - Making Of 6

Hello,

It’s time to talk about picture editing.
It’s an ample topic, we could make

a tutorial series on this topic alone,
I’ll only have two videos and will stick

to a few principles and methods without trying
to cover everything. I guess you can find

additional information elsewhere.

I’ve seen many presentations where
the laudable intent of adding visuals

was marred by a clumsy realization. For
instance, an introductory class to

programming often starts with an
historical overview where is mentioned

the first mechanical computer designed
by Blaise Pascal when he was 19 years old.

Too often, it appears a bit like this.
I’m sorry, but it looks like “our class trip".

I wouldn’t mind seeing something like this

in a junior high-school presentation, but
it doesn’t look professional. Yet you’ll often

see it, in a company, during a class, or
at technical conferences.

There are several possible ways to well
integrate a picture to a presentation.

First solution, the full-screen image,
much loved by Garr Reynolds, among others.

There may be a slight issue with text if
you have some (which isn’t mandatory)

because contrast can be poor. In
that case, a solution may be

to paste a rectangle, a shape, over the text,
to change the fill color of this shape

to white or light grey, to
make it say 50% transparent,

then, by playing with how elements are
stacked over the slide, to place

the rectangle between picture and text. Small
but important point, make sure that

this rectangle lines up on at
least one side with an edge,

a rectangle lost in the middle doesn’t
look too good.

Another solution, which I like better
but isn’t always an option, is

to find a color with a strong contrast with
the background image. If your image is a succession

of very light and very dark areas under
the text, the transparent rectangle remains

the backup solution.

Unfortunately, it happens that the only
suitable picture you find on a topic is

small. And in that case, when you increase
its size to the screen size, pixels

appear. Ugly. This problem usually becomes
a concern when the smaller dimension of your

image is under about 700 pixels, and
unfortunately I have already seen

images that ugly in professional presentations.
There are two tactics for coping with it,

camouflage or living with it.
For camouflage, if you are using Powerpoint

the image menu shows on the left something
called “filters”. You can

experiment with different filters, I’m
using here fore instance the one called

“Line Drawing”. It hides a bit too much,

but you can adjust transparency that
I am here increasing from 25 to

50%. Additionally, I’m going to play with colors
and desaturate them, that means making

then greyer so that visually the image pulls
back a little. You can argue about the filter

choice, you may like or not and I’m going
to show you soon something that isn’t

in Powerpoint and that I find better,
but one sure is certain, it’s that it’s

the same image, in the same resolution as before,

and pixels have vanished.
If you prefer living with it, keep your image

small enough so that resolution remains
acceptable but make it look like a

a paper picture by adding to it a narrow white
margin and a shadow, one of the standard

image formatting options. Icing on the cake,
tilt the image a little.

This works very well if you have
several images on the same topic,

with none of them astounding but that
work well as a set.

As long as you have a good enough
resolution (or if you cheat),

full-screen display is a nice solution
but prevents from having more than

a few words on the slide. The most flexible
solution is probably to remove the image background

to only keep what is truly interesting.

Once again, the Powerpoint image editing
menu shows a button labelled

“remove background” which is a rather
impressive tool.

I’ve used it for instance to erase the grey
background of this stamp.

The only snag is that, as with everything that is
automated, result quality varies.

It will be excellent with a strong contrast
between the background and the foreground,

but when you have to guess the edges there are
some worries. For instance, I couldn’t do

any better than this with Pascal’s computing
machine. You can see that there are

several points where obviously
software couldn’t clearly identify

the edges, and showing something as
approximate is embarrassing in a

presentation.This result, I got it
by hand.

The tool I use for editing images
is Gimp, which is not only free but

also a fantastic tool that I have as
happily used on Linux, Windows,

and Mac. There are many books
on Gimp, I will only give

a very very brief overview of techniques
I find useful for making images more

suitable for a presentation.
For instance, hiding pixels.

Gimp has a wider range of filters than
Powerpoint. First, you open the

small image, and resize it with the Image/Scale
Image menu so that its smaller dimension

is in the 750 to 800 pixels range.
The resulting image isn’t pretty,

but there is in the filters menu
under“Artistic” something which I like

much and is called “oilify”,
in other words “oil painting”.

Basically, pixels will turn to paint
spots with an ajustable radius

the default value of which is 8. I often
bring it down to 3 when I want to keep some

detail. Here I’ve kept default parameters.
In the “Colors” menu, I can adjust hue

and saturation. As with the Powerpoint filter

I’m going to desaturate my picture.
Now I can export it to a .jpg or .png

file (beware, it the latest Gimp
versions “Save” writes images in

an XCF format only used by Gimp).

I just have to import it into
Powerpoint, add text, here with

fancy “period” fonts and you’re done.

But this kind of easy transform is just a
drop in the ocean of what Gimp allows

you to do. I was previously mentioning
background removal, and I first need

to tell you a couple of things about
images and Gimp.

Firstly, images that you will find will

mostly be .JPG files (pictures, generally
speaking), .GIF files (drawings and logos),

or .PNG files (everything). Removing the background
implies that the format can display transparent areas,

which .JPG files cannot do. Many interesting
Gimp features are similarly unavailable if you

keep the special color encoding of your .GIF files.
With Gimp, the original format matters little:

it can convert everything. However, it’s best to export

your edited image as a .PNG file when you are done
(and if you save an image before it’s completely

modified, it’s better to use the .XCF
Gimp file format).

Before you start working on a file, you must
make sure of two things. First , in the

Image/Mode menu, that the RGB option is
selected. It won’t be the case if you

have opened a .GIF file. Select this
option, otherwise many options will be

deactivated in menus. Next, transparency.

Go to the “Layer” menu and check

the transparency submenu. If option
“Add Alpha Channel” is deactivated,

it’s OK, your image can be transparent.
Otherwise, select it. Whatever is

transparent is displayed in Gimp as
a grey checkerboard.

Now let’s take a look at tools. Depending
on the Gimp versions, some windows

may or may not be opened at launch.
If they aren’t, you must select them

from the Windows menu. The first, almost
mandatory one, is the “Toolbox”

Don’t be scared by the impressive number

of tools, I always use the same small set

of easy tools. The other window
is the one called “layers”,

As you’ll soon see, some changes require working

on multiple copies of the image, which
you stack up and change separately.

Finally, the last useful window is
the one called “Tool Options”,

which associates with each tool in the toolbox
specific options.

I rarely change options, but this window
is very useful for some tools such as

the eraser, the size of which you often want to change.

To remove the background, the best tool is
the lasso, which allows you to circle

around parts of an image. Using it is simple.
First of all, I advise you to zoom as much

as possible on the area of interest.
Then, either you keep the mouse clicked down

and follow any curve you want, or, what I
always do, you draw straight line

segments and only click to change direction.
With an object with mostly straight edges

such as Pascal’s machine, straight lines are
the obvious choice. When the image is almost

fully circled, double-click and Gimp will
close the loop and indicate that the

circled part is selected. It’s not this part that
we want to remove, but everything else.

Therefore we’ll go to the ‘select’ menu,
click on ‘Invert’, then cut from either

the ‘edit’ menu or by using usual keyboard
short-cuts. At this stage, there will

be certainly some small details to
improve and, if the image isn’t

very geometrical, there may be significant
work to be completed. Here, your tool

will be the eraser. Default options are
very good, the only thing that you may

have to change is the size, and it’s
better to zoom strongly over the area

that you are working on. If you make a wrong
move, no panic, you can undo everything

with Gimp. I’ve made a lot of wrong moves ..
Here is for principles, next

time a practical example.