Pixelated rendering when calling texture2D() in fragment shader

[alexolotl]

I'm using a headless-gl context to bind a ImageData object to a texture, which is then being passed as a uniform to a fragment shader. The resulting image being rendered after sampling the texture in the fragment shader, however, is a blocky/pixelated version of what I'm expecting it to be.

Does anyone know where I might be going wrong here? Thanks!