Opening a ROI File

The ROI file type is primarily associated with ImageJ.

ROI	File extension: ROI
	File type:	annotation file

What is a ROI file?

ROI files mostly belong to ImageJ. ROI files store data that defines a specific area within an image, known as the region of interest. They do not contain the image itself but provide coordinates and boundaries used to mark areas for detailed analysis.
These files are mainly used by imaging programs to annotate or measure parts of an image. They can exist in multiple formats, some of which include binary formats like Microsoft Compound or text-based formats such as UTF-16 (LE) and JSON.
Common use cases include:

Image Annotation: Tools like OsiriX, ImageJ, and ENVI Classic use ROI files to mark and save specific image regions.

Report File Format: In some cases, ROI files serve as read-only report inputs and are stored in a Microsoft Compound format. They are used with applications such as Crystal Reports (Crystal Reports).

Game Save Data: A few ROI files use a JSON structure to store game progress, as seen in games like Realm Grinder.

FilExt.com tip: This file is a container for region annotation data. It is best to open it with the original software that created it to ensure correct interpretation of its structure.

How do you open ROI files?

You need a suitable software like ImageJ to open a ROI file. Without proper software you will receive a Windows message "How do you want to open this file?" or "Windows cannot open this file" or a similar Mac/iPhone/Android alert. If you cannot open your ROI file correctly, try to right-click or long-press the file. Then click "Open with" and choose an application. You can also display a ROI file directly in the browser:. Just drag the file onto this browser window and drop it.

Online ROI Text Viewer

Choose your .roi file to analyze

or drag and drop it here

Online File Viewer

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ROI file format details:

To view or edit ROI files you need to know the file format, because it determines how the data in this file is stored. The file format can be determined based on the file extension and the signature (the first few characters of a file). However, different programs can use the same file extension. Furthermore, a file extension can be renamed incorrectly and double-clicking on it will then display an error when it is opened. So a detailed analysis of a file is vital in order to determine the format and the associated program. In the following you will find our evaluation of the ROI files:

The ROI file ending includes different formats for the applicable programs. The following file formats are most commonly found in ROI files:

• 40% of all ROI files start with the bytes 04 0B 73 74 72 65 61 6D 74 79 70 65 64 81 E8 03, which are crucial for this file format. The contents of these files are partially readable by a human. The files are on average 15 KB in size and range from 1 KB to 15 KB. The file type was developed only in the last few years. The files contain the following words: NSArray, NSMutableArray, NSObject, NSString, streamtyped, NSNumber, NSValue and {{2964.62, 3427.98}, {75, 19}}. An example of a file name is 20586908.roi or 20586934.roi. These files are attributed to muscle.
• 25% of all ROI files start with the bytes Iout, which are crucial for this file format. The contents of these files cannot be read by a human; only a computer program can interpret the data. The average file size is 490 bytes with most files being between 130 bytes and 3 KB in size. The following keywords are characteristic: Iout. The file name 0022-1059-0859.roi is characteristic of these files.

All other ROI files (35%) have no consistent format, such as DOC, JSON and JoeB. Tagged as contest, samples, grss, ieee, interes, region, berke or zona. Just click the "Choose your .roi file to analyze" button on this page to find out what your ROI file is.