Farrow and Ball All White
Thought my experiences may be of help to others.
For various reasons based on decor and room I recently decided the best way forward was to paint my chimney breast as a projection screen, and hang a picture on it when the projector was not in use.
Most white paints aren't white, even the ones with names like absolute white. The whitest I could find, (and it has no obvious tint at all), that was easily available was Farrow and Ball's All White. This compared favourably in price to special projector screen paints. I had read that an American Sherwin Williams white paint had beaten in tests a Stuart screen, so I had some hopes of a good picture.
Those people testing the SW paint had recommended not to go matte, but to have something along the lines of eggshell, (glossy paints are a no go due to hot spot reflections of the projector light or other light sources). For Farrow and Ball it was either a total matte emulsion, modern emulsion, (wipeable and 7% sheen), or eggshell, (20% sheen and not water based). Fearingf I might hotspot with eggshell and in mind it wasn't really for walls I went for the modern emulsion.
After removing the wallpaper to reveal a fairly flat surface, I spent a lot of time filling in a deep chase acros the top of the fireplace that routed the centre and left speaker cable. I did this with deep non drillable filler. I finished off other minor imperfections and the chase with fine surface filler. There was a lot of layered application and hand sanding with very fine sandpaper. Eventually I thought it was good to be painted.
On various advice I wasn't using a foam roller, but a medium hair one, (small pattern good coverage), and had used the All White mixed with about 20% water as an undercoat. Undercoat plus two further proper coats on and we were ready to go. I hoped for acceptable images, but had resigned myself it probably wouldn't be as good as the £100+ screens and screen material I'd used before.
However, I found I was wrong. The picture is at least as good as any of these, starting off with the previous callibration for my last screen, and now with a fresh calibaration to the paint. It seems to me more detail is reveled, (maybe the paint texture is closer than the screen texture), and colours seem better, with a better ability to reveal different colours in the same scene. I'm seeing bits of colour I hadn't noticed before. I think the white may be a purer white possibly. Obviously it's hard to quantify the difference, but I'm pretty sure the paint is better and certain the paint is at least as good as the screens. I still have a screen so may compare directly when I have time.
Also to note that despite my sanding efforts, after painting I diod find the odd small sticking out bit or slight crater or gouge. I thought I may have to sand again, but these cannot be noticed. Also, as before no great effort has gone into ensuring that the wall is flat overall. There are no geometry issues or pan ripples, issues I have had with both portable pop up screens and trying to stick screen material directly to a wall. Small variations in flatness and small imperfections don't seem to register on projected images, even close up.
So I'll be doing some more calibrating of the image, but very happy with this so far. If you think painting a wall is the way to go for you don't be afraid to try it, and you don't need to take a dip in image quality, buy expensive specialst paints, or mix up exotic paints based on internet recipes.