IronOCR: How to Determine Rectangle Coordinates for OCR Region Detection

Overview

Some IronOCR methods accept a Rectangle so you can run OCR on one part of an image instead of the whole thing. This article shows you how to read the four values that Rectangle needs — x, y, width, and height — straight out of Microsoft Paint.

The constructor looks like this:

Rectangle(int x, int y, int width, int height, MeasurementUnits units = MeasurementUnits.Pixels)

Each value means:

Parameter	Description
`x`	Distance from the left edge of the image to the start of your region
`y`	Distance from the top edge of the image to the start of your region
`width`	Width of the region you want to read
`height`	Height of the region you want to read
`MeasurementUnits.Pixels`	Tells IronOCR the values are in pixels

Coordinates start at the top-left corner of the image. x grows to the right, y grows downward:

Prerequisites

Microsoft Paint (or any editor that shows the cursor position and selection size in pixels)
The image you want to run OCR on
IronOCR added to your project

Steps

Open the image in Microsoft Paint.
Move the cursor to the top-left corner of the region you want to read. This is your starting point. Read the cursor position from the bottom-left of the window. In the screenshot below it shows 2403, 1653px, so:
X = 2403 Y = 1653
Use the Select tool and drag a box over the target text. Paint shows the size of your selection in the bottom-left. In the screenshot below it shows 1031 × 214px, so:
Width = 1031 Height = 214
Build the Rectangle from the four values you just read. For the Testing123 region above:
```
var rectangle = new Rectangle(2403,1653,1031,214,MeasurementUnits.Pixels);
```

Pass the rectangle to IronOCR to crop the image down to that region:

var rectangle = new Rectangle(2403,1653,1031,214,MeasurementUnits.Pixels);
ocrInput.LoadImage(frame, rectangle);

Notes and Limitations

The 1031 × 214px value in the status bar is the width and height of your selection. It is not a coordinate.
The 2403, 1653px cursor readout is the X and Y starting point (the top-left of the region).
Do not use the full image size (here 4960 × 7014px) as the rectangle size. That selects the whole image, not your region.
Paint reports in pixels, so pass MeasurementUnits.Pixels to match.
You read these values by eye, so they can be off by a few pixels. If the crop clips part of the text, widen width or height slightly, or lower x or y.