Scanner Auto Crop | When to use the Detect Paper Size Function

scanner auto-crop detect-paper size

The Scanner Auto Crop function is one of the most important features a scanner has.

To see a scanner automatically detect paper size, still amazes me today. But it is not something you notice or even feel on a day to day basis.

From this article you will learn the following aspects:

  • How a scanner automatically detects the paper size and does auto crop
  • How to use auto crop efficiently
  • When you should disable auto crop

How a scanner detects the paper size

First of all, let’s separate the two functions initially:

  • Detect Paper Size – this refers mostly to the scanner, it’s sensors and the actual physical scanning process.
  • Auto Crop – This means the software takes scanned images and crops them to the edges of the document

There is sometimes a bit of confusion between the two terms. Some scanner manufacturers use exactly the name “Auto Crop” or “Detect” for their functions, and it can get a bit confusing.

Detect Paper Size

As I’ve said before, detecting the paper size is up to the scanner.

When documents go through the scanner, it’s not very often they have the same size.

In order not to get constant jams and downtime in production, scanner manufacturers are using presence sensors. They constantly monitor where the paper is in the machine.

They don’t only serve to detect paper size, they also monitor where jams occur, where the paper is at all times, or if debris or small papers are left on the paper path.

To get back, the sensor monitor when the paper enters a zone of the scanner and when it exits that zone. If you combine this information with the information from the other areas of the scanner, you will always know where the paper is at all times.

More important, given that you know the speed of the rollers and you know the precise time a sensor is activated, you can calculate the length of the paper.

This way, when the entrance sensor is activated, the scanner starts capturing the image, and when the exit sensor is deactivated, the scanner stops the capturing process.

At this precise moment, the scanner has captured what it considers to be a document.

Auto Crop

This is an interesting feature. This function works entirely through software processing. Yes, in some cases it will collect data from the scanner sensors, but it’s mainly software.

If we start where we left with the function that detects the paper size, we now have a captured image. This image can’t be delivered yet, as the initial cropping is not accurate. If you look carefully, your image contains a lot of black around your document.

This black color functions more or less like a “green screen”. The software detects where black is in the image and eliminates that part.

Considering the process is accurate, you will see a perfect scan of your document on the screen. Yes, there is a bit more science to this.

But I recommend you focus on understanding basics and how it affects the end result. It’s more practical.

How to use auto crop efficiently

While this is a good feature, leaving it on all the time, will slow down the process a bit.

Most likely you won’t feel this decrease in speed. Still, as you start scanning thousands and tenths of thousands of documents, these add up.

So when exactly should you have auto crop enabled:

  1. A batch of mixed size documents – Probably this is the most obvious answer. When the batch contains documents of different sizes, there is no other way to do it. The increase in productivity that this feature offers is huge.
  2. The batch has not been checked before scanning – Yes, such situations do exist. There are different organizations that have to scan on the fly various batches. They don’t check it before scanning. They just want to put them in the feeder and hit scan.
  3. You use only a couple of scanning profiles – This one is more interesting. In organizations where you can’t always build and edit profiles, you will probably use a standard profile. The profile has to offer you basic scanning, as quickly and efficiently possible.
  4. Projects with complex indexing – This last situation is interesting. Especially in public organizations, you need the document numbering to be continuous. Therefore, you will only use 1 or 2 profiles at most. Given that, you must be ready for any type of document, as rescans can be quite tricky.

When to disable auto crop

While the auto crop function is useful, you will have to switch it off sometimes. Most of the time though, it should be enabled, especially when you scan documents.

To understand this better, it all comes down to the accuracy of the cropping. So most of the times, you will be switching it off because it is delivering bad cropping.

But what are those situations that require this function to be disabled?

  1. The document has a non-regular shape – When you have a lot of documents that are non-regular in shape, I suggest you disable this feature. Yes, the end result won’t be bad, but you will have a lot of false jam alerts and frequent rescans. This results in low productivity.
  2. Solid color up to the document edges – In this situation, you will find it especially tricky. Again, you will have mixed results. When you have mixed results, you start to lower your general productivity. Solid color all the way to the edges affects the cropping process.
  3. Documents are identical in size – Are you scanning batches with identically sized documents. Well, adjust the paper size in the scanner to your size, disable auto crop and hit scan. You will get an increase in speed of about 15%. This is because there is less processing going on.
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