Display Resolutions
This page details the various display formats and resolutions used in the Portsdown Transmitter.
Pi Camera
The native resolution of the Version 1 Pi Camera is 2592x1944. The version 2 camera is 3280x2464. These resolutions are always downscaled in the Portsdown Transmitter.
Video from EasyCap
The Fushicai EasyCap (as sold by the BATC Shop) outputs 720x576 in PAL mode, and 720x480 in NTSC mode. This mode can be switched by making selections on the Portsdown Console Menu or the Touchscreen menu. The PAL/NTSC selection on these menus ONLY adjusts this input mode; no other settings are changed.
Raspberry Pi Framebuffer
The Framebuffer on the Raspberry Pi 3 is 720x576 when set to PAL output mode. If set to NTSC output mode (by manually editing /boot/config.txt) the resolution is 720x480. Note that all the graphics, test cards and image overlays are sized to work correctly in PAL output mode. Some overlays will spill out of the picture in NTSC output mode. NTSC output mode is not tested or supported.
Raspberry Pi Analog Video Output
As of Software Release 201707120, The Raspberry Pi Analog video output (available on the 4-way 3.5mm jack) is set to output PAL at 720x576@50i. If set to NTSC mode (by manually editing /boot/config.txt) the resolution is 720x480@60i. Some overlays will spill out of the picture in NTSC output mode. NTSC output mode is not tested or supported.
The Waveshare 3.5 inch screen is 480x320. Note that this is a 3x2 aspect ratio, not 4x3, so some vertical compression (flattening and widening) of the transmitted image occurs.
The Waveshare 4 inch screen is 480x320. The screen image is inverted compared to the Waveshare 3.5 inch screen, so there is a menu selection in the console to specifically select this screen.
Element 14 7 inch screen
The Element 14 7 inch display is 800x480 pixels. This display currently works in the transmitting modes of the Portsdown if "TonTec35" is selected as the display type in the Portsdown Console Menu. Note that fitting this display disables the "Composite Video Output" and VideoView modes. This is because it creates a new framebuffer and directs all imagery towards itself and not to the composite video output. Additionally, the VideoView mode is tailored to the GPIO-connected touchscreens, and only writes to them.
Transmitted Resolution
The transmitted resolution depends on the mode, FEC and SR:
The default CAMH264, ANALOGCAM, PATTERN and CONTEST resolution is 704x576@25p. If the calculated video bitrate (from SR and FEC) is below 300K, this is reduced to 352x288@15p. and for video bitrates of less than 150K it is further reduced to 160x140@15p.
The default CAMMPEG-2 and ANALOGMPEG-2 resolution is 720x576@25p. If the calculated video bitrate (from SR and FEC) is below 300K, this is reduced to 352x288@15p. The CARDMPEG-2 resolution is 720x576.
Receiver Compatibility
There is no concept of a "PAL" or an "NTSC" DVB-S or DVB-S2 receiver. When PAL or NTSC is used in the receiver description it may refer to an analog video output from the receiver. What has been noticed is that some DVB-S receivers designed for use in North America do not decode 720x576 resolution and were manufactured on the basis that they would only ever receive 720x480 signals; as such they are not fully DVB-S compliant. Note that there is a flag in the datastream to indicate if a digital signal was originally coded from a PAL or NTSC signal. This flag is not used in decoding, but may be used in be professional receivers to assist in the reconstruction of an analog signal.