The transmitter program window
Menu
'File/Exit' closes the program. 'Soundcard/Audio properties' and 'Soundcard/Mixer Output' allow you to select and adjust the
computer sound card for transmission from within the program.
In movie mode, this program is capable of transmitting MPEG1 and MPEG2, but for this you may need to change the video accelerator setting, hence the extra 'Video Accelerator' menu item. 'Movie frame rate' allows you to select a replay speed, or synchronize it to the source movie, one frame at a time.
Tabs
There are three tabs which can be selected: 'Still picture', 'Movie' and 'Webcam'. You can select any one
of these and transmit the appropriate image. You can also 'preload' some of these for instant switching and seamless
transmission. Whichever tab is currently showing is the one which will be transmitted in the next frame. All the tabs
except Webcam accept 'drag and drop' selection of pictures (just drag the picture from
an Explorer folder onto the appropriate tab). You must 'drop' the correct type of picture or the program will complain.
On the 'Still picture' and 'Movie' tabs the current file name is displayed at the bottom of the tab.
The whole picture seen on the tab is transmitted. It does not matter what size the original picture is, as the program will resize it to suit (although it does not change the aspect ratio). Even if a B&W image is selected, the transmit program still transmits colour information.
If the picture has an aspect ratio other than 4:3 (landscape mode), the picture will be adjusted to fit the width or height of the frame appropriately, and the unused space transmitted as plain background colour. In other words, if the picture is very long and thin, the top and bottom will have unused space, and if it is tall and narrow (4:3 portait shape for example, as shown in picture on right), the sides will have unused space. A 4:3 (landscape) picture, such as a camera or TV picture, fits perfectly. The background colour transmitted for the unused space is the same grey as the window background.
Still picture Tab
With the mouse, you can 'drag and drop' any still image onto the 'Still picture' tab to be transmitted. This tab accepts all the
following image formats:
- .BMP
- .JPG
- .GIF
- .PNG
- .TIF (most)
Movie Tab
This tab will play movies! The transmission is of course very slow, but at the receiving end the frames can be
recorded and then replayed at full speed. You can set (from 'Frame rate' on the menu) the
frame rate of the transmission (frames per second). For example, with a 3-sec frame rate on a 9-sec transmission,
two out of every three frames in the original file are skipped. There is also a 'Sync frames with sender' option.
Open the file to be played from the File menu (top left), or drop it onto the tab from a folder list. The controls at the bottom start/stop the AVI file and show/adjust the position within the file. While the program is in pause (the '||' button pressed), transmission continues: the frame showing during pause will be transmitted over and over.
Webcam Tab
This tab uses any TWAIN compliant video source, such as a USB 'web' camera, TV capture card or TV receiver card. It will
even work with a scanner! With the TV devices you can use images from conventional video input from a camera or digital still
camera, live off-air TV,
or TV camera with RF modulator. If you plan to use a USB webcam, make sure you plug it in and allow it
to initialize before you start the TX program, or it won't be recognised. In addition, in order
to use the webcam, click on the 'Enable Webcam' button at the bottom right of the window. You need a
dual-core Pentium 4 3GHz computer to use this tab. The extra button is added
to allow slower computers to operate with still pictures without the extra burden of the Webcam driver software.
From these devices one frame is captured whenever it is needed, so many are missed. The Webcam tab shows the video source with colour and full motion, but remember that the transmitted frame rate is slow, so don't pan the camera around or expect to transmit movement.
Two extra buttons appear at the bottom of this tab - one to select the video source (if you have more than one), the other to select video format. Any format should work, and you don't need more than 288 x 384 pixel resolution. Higher resolutions require more processing power from the computer, but don't change the transmitted picture size or frame rate.
Always on top
Under the Transmitter applet picture pane there is a check box labelled 'Always on top'. When this is ticked
(and it is by default), the transmitter applet stays above all the other windows on the screen. If you uncheck this
option, the transmitter can be buried under other applications.
About the only advantage of this is that you can then transmit pictures of formats not supported by the program,
through the simple expedient of dragging them over the top of the TX window. Remember that the image
has to be small enough to fit on the transmitter active area. It is the top of several layered application windows
that will be visible to the transmitter. This technique is a bit tricky, as you cannot see where to place the
window. The technique overrides all the transmitter tabs.
Negative modulation
In some circumstances noise on received pictures will be less if the modulation sense is reversed. This of course
needs to be coordinated with the receiving station. The default is negative modulation.
Preserve still picture aspect ratio
It was mentioned under the Still picture tab information that portait format pictures will be transmitted with
grey space on either side, since the transmissions are always landscape format. This is the default procedure.
You can however, unclick the 'Preserve still picture aspect ratio' control, and transmit such pictures stretched full
width (example on right). This has the advantage of using all the available image resolution. The receiving station
can restore the correct appearance by manually (with a graphics editor) changing the image aspect ratio back to 3:4 once it has been saved.
