Above, you can see an image full of different colours.
One possible way to generate this image is by using a linear gradient rotated 90 degrees, however, this may not be the only way.
Your task is to create a self-contained program that takes no input, and outputs an image with the same RGBA pixels as the above image, and in the exact same location, with the output image being in a file format that was created before this challenge, with the dimensions of the image being 4096x4096px, same as the original.
The shortest such program, scored in bytes, is the winner.
Cheating and standard loopholes are not allowed.