P: Stroke border on export

You can use this plugin:
https://lightroomtoolbox.minsky.com.ar/en/bordes/

It lets you to add simple and complex frames. There are three types of frames:

• internal: they partially cover your photo (you define the border thickness, color, transparency)
• external: arround your photo (you define the color, transparency and thickness in any direction)
• frame: they are around your photo. it is used to complete a defined aspect ratio for instance if you like to export photos with different aspect ratio and want to get all exported files with a 4:5 aspect ratio or whatever you want. (you define the aspect ratio, color, minimum thickness and whether the photo will be centered)

• All those types can be combined and used together
• external and frame borders can use you photo for its definition. The photo is expanded to cover the border, and you chooso a blur, desaturatioin and transparency that will be used. This creates a border that combines with your photo
• All those types have inner and outer contourns you can define
• You can also add shadows in order to create volume (for instance a countour representing the wooden part of the frame project shadow so you get volume)

A keyline is a thin border around the outside of the image, used to help make the edges of the image distinct from the background it is displayed on. The width of the key line is typically 2 or 3 pixels for an image exported with a width of 1600 pixels. For black images on a black background it might be white or light grey. For white images on a white background it might be black.

This means there are two parameters the user needs to be able to specify:

1. The width in pixels of the keyline AFTER the image has been resized to the specified dimensions
2. The colour of the keyline

It might be useful to be able to specify whether the keyline lies outside the boundary of the image or within it but in either case, the dimensions of the exported JPEG/TIFF &c should remain at the specified size.

While this can be done currently using Photoshop, that approach has two disadvantages:

1. We need to export a lightroom image to Photoshop and create another TIFF or PSD file to manage for no other reason that to add this keyline
2. We need to guess how big the keyline needs to be so that it will become two pixels wide (for example) after scaling during export.

(2) would also be true if Lightroom allowed us to do this the Develop module, hence the request for an export setting. Additionally, being an export setting, two export presets could be used so that the same image could be exported with and without a keyline.

I would like the ability to add a stroke / border to an image while in the develop module.  When you print via a 3rd party utility, i.e. Canon printer software, you can add a stroke border.  A facility like the fX - stroke layer in photoshop would be ideal.

Is this not accomplished in the Print module?

How to Add an Image Border in Lightroom.

and a way without using the Print module:

How To Quickly Add Borders When Exporting Photos From Lightroom (Without Using the Print Module)