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.