Live preview

Live preview — also called “digit preview” inside the app — reads the value in your viewfinder straight from the camera stream, before you even tap. QCR Scanner recognizes the target region a few times per second, runs the recognized text through your validation rules, and the moment a value passes those rules it appears in green above the viewfinder. That lets you see in real time whether the phone is lined up correctly, before you tap to scan.

This page explains what live preview is, how to turn it on, how it relates to the capture modes, what it does to battery and heat, and when it makes sense to use it.

What live preview is

In the normal scan flow you tap the viewfinder to capture a value, and OCR and QR scanning run at that moment (see Scanning). Live preview steps in before that: it reads continuously from the camera stream while you have not tapped yet.

• The target rectangle in the viewfinder is read a few times per second.
• The recognized text is run through your active validation rules.
• If a value matches every active rule, it is shown in green above the viewfinder.
• If no value matches the rules, the preview shows nothing — so green text means “tap here and this value lands in the list.”

The key point: live preview on its own does not add the value to a list. It is only a sight. To actually record the value you still need to tap the viewfinder (or use another path such as Smart Extract or voice input).

Tip: Green text means a value already passed validation. As you move the phone toward the target, tap the instant you see the green value showing the right number or text — that lowers the chance of capturing the wrong frame.

How to turn it on

Live preview is toggled from the camera controls on the left arm of the viewfinder. One tap enables it; tap again to turn it off. While it is on, continuous reading from the camera stream begins and a live result area appears at the top of the viewfinder.

The same left arm holds the other camera controls that complement live preview:

Control	What it does
Torch	Lights the target in low light
Focus lock	Pins focus; keeps the preview steady when the stream hunts
Zoom	Enlarges distant or small text in the viewfinder
Viewfinder size	Width/height sliders narrow the target region
Capture mode	Lightning (⚡) / HD button toggles Instant ↔ Quality

If the preview feels noisy or jumpy, use the viewfinder size sliders to tighten the target rectangle around exactly the text you want to read; a smaller, cleaner region makes both the preview and the real capture more accurate.

How it differs from and relates to Instant mode

Live preview and the capture modes are often confused; they are different things that work together.

• Instant / Quality mode decides what happens when you tap. Instant mode (the default) takes the last frame from the warm camera stream and runs OCR + QR in memory immediately, with no shutter, no JPEG encoding, and no write to disk. Quality mode instead takes a full-resolution capture and decodes it natively on the device for the highest accuracy on small, dense text.
• Live preview is a separate reading that runs continuously before you tap, and it only shows a sight on screen.

The relationship is this: live preview also does fast reads from the camera stream, just like Instant mode, so it pairs naturally with Instant mode — both work on the “fast result from the warm stream” idea. After you see the green value in the preview and tap, Instant mode grabs that frame immediately. If you choose Quality mode, the preview still gives you a sight, but the value that actually gets recorded is the result of the full-resolution frame taken at the moment you tap. In short, the preview tells you “you are lined up right now,” while your mode determines the quality of the capture itself.

Note: The green text you see in the preview is a candidate that passed validation, but the final value comes from the scan at the moment you tap. Especially for small, dense text such as serial numbers, hold the phone steady just before tapping.

Battery and heat

Because live preview reads the camera stream continuously and runs OCR every few hundred milliseconds, it does more work than the viewfinder does while sitting idle. That has two practical effects:

• Battery drains faster — the camera, screen, and OCR are all active the whole time.
• Warming can occur; over long, uninterrupted sessions the phone may get warm.

This is normal and not a sign of a fault. If you are only scanning occasionally, or once you are confident about alignment, turn live preview off and switch it on only when you actually need it. Other ways to save battery: keep zoom modest, use the torch only when needed, and avoid keeping the viewfinder region larger than necessary.

Tip: During a long counting or inventory session, if the phone warms up, turn the preview off for a stretch and scan by tapping only; that lowers heat and extends battery. Validation still runs on every tap.

When to use it

Live preview is not required for every scan; it pays off most in these situations:

• When you are not sure of the alignment — with an angled shot, glare, or a shaky hand, you can move the phone until the green value appears and catch the right frame.
• On small or dense text — for hard-to-read targets such as serial numbers or meter values, you confirm it reads correctly before tapping.
• When trying out a new rule set — you see live whether the validation rules you wrote actually accept the values you expect in the real world.

By contrast, if you are doing fast back-to-back scans from a fixed, clear label, keeping the preview off and just tapping is both smoother and easier on the battery. And when you want to pull several values at once from a single block of messy, multi-part text, Smart Extract is a better fit than the preview.

Live preview is part of the camera-stream capabilities of QCR Scanner, made by ReviseTouch.

Next steps

• Scanning — the viewfinder, target rectangle, and Instant/Quality capture modes
• Validation rules — the regex-based accept/reject rules that drive the green preview
• Smart Extract — automatically pull several values from noisy text
• Quick start — make your first scan in under a minute