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Hello,

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

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

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

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additional information elsewhere.

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

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

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programming often starts with an
historical overview where is mentioned

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

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

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I wouldn’t mind seeing something like this

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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the backup solution.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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the same image, in the same resolution as before,

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

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

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

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

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

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

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

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

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

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to only keep what is truly interesting.

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

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“remove background” which is a rather
impressive tool.

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

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

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

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

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

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several points where obviously
software couldn’t clearly identify

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

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presentation.This result, I got it
by hand.

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

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

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

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

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suitable for a presentation.
For instance, hiding pixels.

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

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

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

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

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

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

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

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

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and saturation. As with the Powerpoint filter

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

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

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an XCF format only used by Gimp).

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

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fancy “period” fonts and you’re done.

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

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

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

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Firstly, images that you will find will

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

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

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

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

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

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

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

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

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

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

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deactivated in menus. Next, transparency.

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Go to the “Layer” menu and check

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

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

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transparent is displayed in Gimp as
a grey checkerboard.

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

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

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

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Don’t be scared by the impressive number

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of tools, I always use the same small set

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

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As you’ll soon see, some changes require working

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

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

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which associates with each tool in the toolbox
specific options.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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time a practical example.