VGA and Older Devices

Why VGA is different from HDMI

ReadForce works by capturing the digital video signal that your device is already producing. Modern devices output HDMI, DisplayPort, or USB-C video — all digital signals that carry clean, exact pixel data frame by frame.

VGA is an analogue signal. Instead of sending pixel values as numbers, it sends continuously varying voltages for red, green, and blue channels. A VGA display reconstructs the image from those voltages. The result is visually similar but technically very different: there are no discrete pixels, the signal is susceptible to electrical interference, and the quality depends on cable length, connector quality, and the age of the hardware involved.

For ReadForce to capture a VGA source, the analogue signal must be converted into a digital one before it reaches the capture card. That conversion is entirely possible — and two well-established hardware paths exist to do it.

Two hardware paths that should work

Direct VGA-to-USB capture card

Instead of the standard HDMI capture card, a dedicated VGA-to-USB capture card can be connected directly to the Raspberry Pi. The VGA cable from the old laptop plugs into the capture card; the capture card plugs into the Pi's USB port.

Many of these cards are built on the UVC (USB Video Class) standard, which means they are driver-free and natively supported by Linux and the V4L2 framework that ReadForce already uses. In principle, the existing software pipeline — FFmpeg, OpenCV, Tesseract, and Piper — would work without modification.

No changes required to ReadForce software
Replaces only the capture card hardware
UVC compatibility means Linux driver support out of the box
Needs testing to confirm specific card models that work reliably

Typical retail price: £10 to £35

Active VGA-to-HDMI converter dongle

This option keeps ReadForce hardware exactly as described in the white paper. A small active converter dongle plugs into the laptop's VGA port. Inside the dongle, a chip digitises the analogue signal and outputs it as standard HDMI. That HDMI cable plugs into the existing ReadForce capture card.

Once the signal has been converted, ReadForce has no awareness that it originated from a VGA source. The software pipeline does not change at all.

It is important to use an active converter, not a passive cable adaptor. VGA is analogue and HDMI is digital; a passive cable cannot perform the conversion. Only an active converter with a conversion chip will work.

No changes to ReadForce hardware or software
Only an external dongle added between laptop and ReadForce
Widely available from electronics retailers
Must be active — passive adaptors will not work

Typical retail price: £8 to £25

The analogue signal problem for OCR accuracy

Both hardware paths are technically viable, but there is one important caveat that users should understand before relying on VGA capture for ReadForce.

OCR accuracy may be lower with VGA sources

ReadForce's Tesseract OCR engine performs best when it receives sharp, high-contrast, clean-edged text. Modern HDMI and USB-C sources deliver exactly this — each pixel value is transmitted as a precise digital number.

Analogue VGA signals can introduce blurring, slight ghosting, and reduced edge sharpness — particularly on older hardware or with longer cables. This can increase OCR error rates and lower confidence scores, meaning ReadForce may misread words or produce garbled output more often than it would from a modern digital source.

ReadForce's OpenCV image preprocessing pipeline — which applies contrast enhancement and sharpening before passing frames to Tesseract — can partially compensate for analogue signal degradation. However, it cannot fully recover a genuinely poor signal. On a clean, well-maintained VGA connection, the difference may be negligible. On an older cable or worn connector, it could be significant.

This is not a reason to rule out VGA use entirely — it is a reason to test in your specific environment and manage expectations appropriately.

What the team plans to investigate

Formal VGA support is not in the current development roadmap, but the team intends to investigate it as documented real-world needs arise. Specifically:

Testing with specific VGA-to-USB capture cards to identify which ones provide reliable UVC-compatible video at sufficient quality for OCR. Identifying whether any preprocessing adjustments to the OpenCV pipeline materially improve OCR accuracy on analogue-sourced frames. Documenting a verified hardware bill of materials for users who need VGA support, equivalent to the current verified component list for HDMI setups.

If you have a specific use case that requires VGA support — for instance, an older machine used in a school, workplace, or care setting where replacing the hardware is not an option — please get in touch. Concrete use cases are the most effective way to move a feature from "intend to investigate" to "actively building".