how to see the same thing through a projector as I see on my laptop

Hello, everyone.

I will be traveling in two weeks to do an Open Office Impress presentation from my laptop connected to a projector. Unfortunately I am not able to determine in advance the brand and model of the projector I’ll be using, and based on problems I am having at home when I connect the laptop to an external monitor I am concerned that what I will see on my laptop during the presentation will not be what the projector puts up on the wall.

I have connected the laptop to an external monitor at home and cannot get both images to look the same. For example, when the external monitor is connected the laptop no longer displays a full screen image and, instead, displays what looks like a 4X3 image in the middle of its screen. At the same time the external monitor (22") displays what looks like an elongated (obviously stretched) 16X9. I have not found a way with settings in YaST or in KMplayer to get both synchronized.

My laptop is a Lenovo Edge E520 running SuSE 12.1 (15.6" display) and KDE.
My home external monitor is a Samsung 226BW (22" display).

I am guessing that I need to reset resolutions somewhere, but I don’t know where to start and don’t want to screw up either the laptop or external monitor by doing something stupid.

So…

Can anyone give me some guidance on what to do if, when I get onsite for my presentation, turn on the laptop, and connect it to the projector I then discover that what I see on the laptop is not what I see on the wall? How do I get it right before the audience arrives and the show begins?

If I need to provide additional information please just tell me what to post.

Many thanks!
socref

The only time cloned displays will behave identically is when the display resolutions of both devices match, although xrandr provides some flexibility to adjust the mode, according to the detected capabilities of each.

What may work for you is to get this info from ‘xrandr’ when you set up, then you may be able to scale the output of the projector to suit. For example, I have two display devices

xrandr
Screen 0: minimum 320 x 200, current 1680 x 1050, maximum 8192 x 8192
LVDS1 connected 1680x1050+0+0 (normal left inverted right x axis y axis) 331mm x 207mm
   1680x1050      60.0*+
   1400x1050      60.0  
   1280x1024      60.0  
   1280x960       60.0  
   1024x768       60.0  
   800x600        60.3     56.2  
   640x480        59.9  
VGA1 connected 1280x960+0+0 (normal left inverted right x axis y axis) 410mm x 230mm
   1366x768       59.8 +
   1280x1024      75.0     60.0  
   1280x960       60.0* 
   1280x800       59.8  
   1152x864       75.0  
   1280x720       60.0  
   1024x768       75.1     70.1     60.0  
   832x624        74.6  
   800x600        72.2     75.0     60.3     56.2  
   640x480        72.8     75.0     66.7     60.0  
   720x400        70.1  

So, I scaled the external display

xrandr --output VGA1 --same-as LVDS1 --scale 1.28x1.37

It does work, but I managed to lock up the X-server playing :slight_smile: so be careful.YMMV

My above demonstration wasn’t carefully planned out. When I adjusted the external display to use the native resolution, and adjusted the scaling as best as I could, I finished up with

xrandr --output VGA1 --mode "1366x768" --scale 1.23x1.37

Bear in mind that the scaling changes the effective image resolution, so it won’t necessarily be as sharp as you’d like. When I worked as a video technician in the event industry, it was common to use scan converters to fulfill this function. These give you a lot more input/output options and can scan and pan the output.

Deano, thanks for this reply. I definitely don’t want to lock up X since I probably might have trouble recovering from that!

Some questions:

  1. What do the columns of numbers represent?
  2. In the “code” you show how did you determine to use the scale of 1.28x1.37? Where did those numbers come from?
  3. If I were to follow your suggestion with xrandr what happens when I am done with my presentation? How do I get my laptop back to “normal?”
    Thx
    socref

Deano, thanks for this reply. I definitely don’t want to lock up X since I probably might have trouble recovering from that!

I’m not sure why that happened to me. It might have been unrelated. Try it for your self.

  1. What do the columns of numbers represent?

The xrandr output shows the display modes that given hardware has been detected of supporting. The second - fifth columns represent vertical refresh timing (not relevant here).

  1. In the “code” you show how did you determine to use the scale of 1.28x1.37? Where did those numbers come from?

You could calculate from the ratio of the horizontal resolutions (each display device), and the vertical resolutions, but I recommend just setting up your projector, and then try scale values. You’ll soon see if you need to adjust the horizontal/vertical scaling up or down. For example, if you start with

xrandr --output VGA1 --same-as LVDS1 --scale 1.0x1.0

then edit the command and execute again a few times with values that ‘size’ the desktop to match your laptop display (ie no cropping, or underscan evident).

  1. If I were to follow your suggestion with xrandr what happens when I am done with my presentation? How do I get my laptop back to “normal?”

Any changes you make with ‘xrandr’ are not persistent. They are only effective for the current session, so you could disconnect the projector, and restart the X-server when finished, or issue something like

xrandr --output VGA1 --off

Of course, your output name may differ, depending on connection type and graphics driver, so adjust accordingly. (These names are reported via xrandr too).

I think you should familiarise yourself with xrandr first

man xrandr

Many thanks, very helpful. :slight_smile:
socref