Which approach should I take to implementing this concept?

Question

I'm planning on creating a simple color lookup table-based painting software in Flutter (one color palette can define colors for every image in a set, the canvas defines a source coordinate and a palette coordinate for each pixel, the color at the palette coordinate gives the color of the displayed canvas), and I'm torn between two approaches due to gaps in my knowledge.

In one approach, I can represent the canvas as cells of a GridView. This would allow me to lookup the color in the palette per-pixel, but I'm not sure how I would take the final info for the layout image and its palette and convert them to an image file format.

In another, I can represent the canvas as an Image widget and use the image library to draw upon it, later converting it to an image with image's functionality. However, I don't know how to implement a lookup per-pixel.

Any help would be appreciated. If I can call an event per pixel on Canvas/CustomPaint I'd be open to that as well. Thanks in advance!