Contrast Adaptive Sharpening (CAS) is a low overhead adaptive sharpening algorithm with optional up-sampling. The technique is developed by Timothy Lottes (creator of FXAA) and was created to provide natural sharpness without artifacts.
It is used in 3D Graphics frameworks like DX12 and Vulkan, and provides a mixed ability to sharpen and optionally scale an image. This project implements only the sharpening part. The algorithm adjusts the amount of sharpening per pixel to target an even level of sharpness across the image. Areas of the input image that are already sharp are sharpened less, while areas that lack detail are sharpened more. This allows for higher overall natural visual sharpness with fewer artifacts. CAS was designed to help increase the quality of existing Temporal Anti-Aliasing (TAA) solutions. TAA often introduces a variable amount of blur due to temporal feedback. The adaptive sharpening provided by CAS is ideal to restore detail in images produced after TAA.
This project implements CAS as a CUDA kernel. The main reasons for porting CAS to CUDA are:
- General purpose. Because CAS is technically a filter, it can also be used for sharpening static images (like local files from disk). The original CAS filter works only in 3D graphics frameworks.
- Speed. By implementing the CAS algorithm efficiently in CUDA, we can expect major speedups compared to CPU implementations by leveraging the GPU's high performance in parallel problems.
Τhis repository has two projects:
- CAS Implementation. The core functionality of CAS, implemented as a CUDA kernel. It is a DLL project, and defines a C-style interface for interacting with the DLL. Programs that will use CAS filtering, should have in the output directory the CAS
.dlland.libfiles, and also include theCASLibWrapper.hfile to interact with the DLL. - Sample usage. This project aims to showcase how to interact with the CAS DLL in order to sharpen images. We can parameterize the sample with the provided
settings.inifile:
| Parameter | Description |
|---|---|
| image | Path to the input image. |
| save_sharpened_file_to_disk | Save the sharpened image to disk, in the same path as the original image, suffixed with "_CAS". |
| execution_time_in_fps | Show how much time it took to sharpen the image and transfer it back from VRAM to RAM in absolute time, or in FPS. |
| sharpen_strength | CAS Parameter. The main sharpening intensity, with values in the range [0,1]. |
| contrast_adaption | CAS Parameter. Lower values reduce sharpening based on the local contrast, with values in the range [0,1]. |
| loops_for_test | Runs the sharpening pass multiple times and averages the time for the sharpening + copy from VRAM to RAM |