PPT/PDF : how to display a mirrored version of my slides? (flipped or flopped)

Question

Rather than a raw text, I want to use my nice ppt slides within a teleprompter, which use a half-mirror.

Text-prompter softwares automatically flip the screen, which is then flipped back by the mirror into the expected readable way.

But PowerPoints doesn't do this first flip display. To counter the half-mirror, I must find a way to output on my screen a symetrically flipped image via the vertical axis (such below but for the whole screen).

At the end, I want something flopped such as :

How can I output a flipped version of my PPT / PDF ?

Answer 1

Flop

As you convert into static images, then rather output pdf and work on it. Then, you can use :

mogrify -density 200x200 -quality 100 -flop *.pdf

It flop your pdf, so you can now use it in a pdf reader full screen, and command the page change using a mouse or other.

Output quality

There may be issues with the output quality and file size. First, if just using mogrify -flop *.pdf, the output is of poor quality. Second, if using mogrify -density 200x200 -quality 100 -flop *.pdf, the output may be of 30 times the initial pdf weight (as far as I saw). This issue is to dig in. See also Convert PDF to image with high resolution

Answer 2

You don't say whether or not you have PowerPoint available. If you do, this is quite simple.

First, save the presentation as a Picture Presentation. That saves it to a presentation containing images of your original slides. Open the picture presentation and run this VBA on it:

Sub thing()

Dim oSl As Slide
Dim oSh As Shape

For Each oSl In ActivePresentation.Slides

Set oSh = oSl.Shapes(1) ' there should be only one shape on the slide

oSh.Flip msoFlipVertical
oSh.Top = 0

Next    ' Slide

End Sub

Answer 3

All the answers which involve ImageMagick tools (mogrify, convert) will first force your (potentially) vector-based PDF through a mincer that creates (possibly very large) pixel data from your slides. Converting that back to PDF will not restore you steak... uhmmm vector PDF, but it will just wrap the pixel data into a PDF shell.

There is an alternative: Use Ghostscript together with a little PostScript code snippet to transform vector-based PDF to vector-based PDF.

Ghostscript's solution

Use -dAutoRotatePages=/None (or =/All or =/PageByPage). Here we require =/None in order to tell Ghostscript should not try to auto-rotate the page(s) so that the text is "readable".

Here are the two complete, working commands to mirror PDF pages for A4-sized documents:

1. Horizontal mirroring (left <=> right):

   gs                                                           \
     -o mirrored-horizonal.pdf                                  \
     -sDEVICE=pdfwrite                                          \
     -dAutoRotatePages=/None                                    \
     -c "<</Install{595 0 translate -1 1 scale}>>setpagedevice" \
     -f input.pdf
   

2. Vertical mirroring (top <=> bottom):

   gs                                                           \
     -o mirrored-vertical.pdf                                   \
     -sDEVICE=pdfwrite                                          \
     -dAutoRotatePages=/None                                    \
     -c "<</Install{0 842 translate 1 -1 scale}>>setpagedevice" \
     -f input.pdf
   

Width and translate

Assuming that the width of the PDF page is 8.5 inches, aka 612 points, hence the 612 0 translate part in my PostScript code snippet.

If your page width is different from 612 points, you have to adapt that part accordingly.

A4 portrait or A5 landscape media: 595 0 translate.

Google doc presentation, 16/9 are 254 × 143mm aka 10" × 5.63 : 720 0 translate.

Answer 4

Split

You can use unoconv to convert your PPT files to JPEGs. See How to convert pptx files to jpg or png (for each slide) on linux? .

# ptt to pdf
unoconv --export Quality=100 filename.pptx filename.pdf
# pdf to multiples jpg
convert -density 400 my_filename.pdf -resize 2000x1500 my_filename%d.jpg 

Flop

Then use ImageMagick to flop them like this:

convert input.jpg -flop output.jpg
mogrify -flop *.jpg #rewrite upon input

You can also flip them, by adding -flip into the command above.

Glue

You can put them back together in a PDF using ImageMagick:

convert page1.jpg page2.jpg pagex.jpg combined.pdf
convert *.jpg combined.pdf 

Other : pdftk ?

I haven't tried, but I think you can use pdftk to put them back together into a flipped PDF too.

Answer 5

Flip & flop the whole display

Linux

Source How can I mirror/flip display output?

Go to console (Alt+F2 then type gnome-terminal and press ENTER)

xrandr -x will flip de video horizontally like a mirror.
xrandr -y will flop de video vertically.
xrandr -y -x will both flip and flop (= invert).
xrandr -o inverted will...invert O.o
xrandr -o normal will return to normal the video.

Rational

It is much simplier and more faithful to flip the whole display rather than to go for tricky, time consuming, buggy file format conversions.