Image Sharpening Techniques & Plugins for Video Footage – Part I – What is Sharpening?
Our eyes can perceive resolution at a level beyond what current digital imaging and displays have yet to reach, despite how advanced the tech currently is.
Digital video imaging and demosiacing add a degree of blur. The physical reality of the fact that lenses cannot be perfect also adds abnormalities such as edge blur to an image, depending on the type of lens and aperture setting it can be inconsistent across the image making the issue more complicated. The real world is analog and we are converting that into discrete samples. Error is unavoidable.
What can cause images to look blurry or fuzzy is that fact that an edge or transition can occur within the area of a single sample (pixel). Since one pixel can only return one singular value, it ends up representing neither side of the real world edge or transition. In a CMOS sensor this value can be any value from 100% Black to 100% White.
Imagine a contrasting line intersecting a pixel. The result after interpolation is the creation of an “in between” solution for transitions which result in edges that we see as blurry /out of focus. This is compounded by the anti-aliasing filters used in many cameras.
Sharpening a video image in post is a way to artificially add detail to the final image. The challenge is deciding what method of sharpening to use, and where to draw the line between sharpness and high frequency noise artifacts.
One of the most common basic image sharpening techniques is the ol’ unsharp mask. On a very basic level it works by blurring the source image and subtracting the blurred image from the original to detect edges. Taking that edge information, the contrast along those edges can be increased which increases sharpness. If you have a properly exposed, perfectly focused image with no motion blur sometimes all you need is a little unsharp mask and you are ready to go.
As with all sharpening methods overdoing it leads to artifacts such as halos and color shifts as well as bringing extra attention to noise and lens aberrations.
Other methods of sharpening video include Edge Enhancement, Deconvolution, and selective masking.
Dedicated plugins can help give video footage a naturally sharper look via edge detection algorithms, local contrast selections, and masking that sharpens only exposure that falls in the middle of the histogram. Part II of this writeup will compare a few of these plugins on some 4K+ footage. Coming soon.