I was never able to figure this out but I just posted the question on LinkedIn in the Apple Motion group. I saw that you asked this question in a few other places including one thread here where someone said they would write Mark Spencer and see if he knew. It looks like they never wrote back so if I find out anything, I'll let you know.
I can't help with the problems with Exporting, other than to say that my personal tests show that Proxy is better than 4x4 with slightly reduced banding artifacts.
However, for the Motion 5 canvas: you should be able to get excellent results if you turn OFF Dyanamic [Resolution] and select Custom [Quality] - and from the popup dialog, check High Quality Resampling. (While you're at it, for Text Quality, check Shape anti-aliasing and Anti-alias 3D intersections — if necessary.) With Dynamic resolution turned off, Motion will stop trying so hard to keep up a frame rate (it won't achieve anyway) by sacrificing some of the video quality while playing (no matter what the quality setting is.)
It looks like ProRes 4444 is actually the culprit here. I tested a similar gradient in Motion 3 inside a 32-bit sequence even with dithering turned on and there was still banding (although much less with dithering selected). If you are able to, send your timeline directly to Compressor or use the "Export Using Compressor Settings" option. Choose the Animation preset and see what happens. I can't test this because every time I try to send to Compressor, the software hangs. When I use the Compressor settings method, the Share Monitor will open but after awhile my job will time out and I get an error. If you can send to Compressor without these issues, I'd love to hear what your gradient looks like as Animation.
I am getting the banding issue also, but it's not just ProRes. The same thing happens when I export a TIFF (or anything else for that matter) whn the gradient is shallow enough. I simply can't export to any format that looks as high quality as it does in the canvas.
Here's my thread on the subject:
Well I was actually able to find the answer and for me it was ProRes or the other codecs for that matter. I found a machine where sending from Motion to Compressor didn't crash and I exported using the Animation preset. It actually looked terrible and then I went into the setting and found out that the preset was on medium quality! So I made a duplicate with the quality set to the highest and exported again from Motion using the Compressor settings and the banding was completely gone. No need to use noise or anything else. The only problem is, the send to Compressor isn't working on my work machine so for now adding noise is still the solution.
Here's a work-around that I found after many tries, but only suitable for fairly small pieces. It moves the final exporting and compression out of Motion. It involves rendering out a good quality frame sequence and audio mix track, then recompiling and outputting to H264 via Blender 3D, which has a video sequencer in it. If Motion or QT pro is on your system, it will access all those codecs.
Blender (from Blender.org) is a bit of a beast, but once the interaction,filing and output aspects are mastered (there are plenty of tuts online), then the video sequencer is surprisingly flexible, and it handles controllable outputting to MPEG1 too, which is a faff in a lot of other applications.
Before exporting the frame sequence, add a noise filter to break the gradient down a bit (try as I might, I could not get Motion to export a satisfactory H264 grad, even with the noise applied, but it did work on exported frames)
Settings for the Noise filter / Summary...
Amount, say 0.02 - 0.03
Blue Noise Type
Uncheck Autoanimate (makes it too fuzzy in render)
Render out to Image sequence on Best
Render out Audio Track mix
Recompile in blender and output to H264 form there (providing QT pro is in the machine). It will be a little slow, and may take a few goes to get a feel of quality vs filesize trade offs.
A few Blender Tips (there is a lot to learn, but here are some navigation helpers)...
Before doing anything set all the render settings first on the default page, making sure to check the sequencer box on the post-pro tab (compositing unchecked).
Then go to the sequencer page and add in the image sequence and audio track (Blender likes Wav)
In Blender, Use right mouse button to select and move, left to confirm (strange, but it makes sense after a while).
To render, go back to the default render panel, enter the output pathe, then click the Animation render button).
Rendering can take a while, but worth temporarily shortening the output frame range to test short sample , playing with the output settings.
@Martian4, that's an incredibly complicated workaround, but kudos for figuring it out. Like I said in a few posts above, the problem is ProRes4444.
@Mike, After Effects isn't going to solve this problem, I just tested a gradient that was very similar to ones I had been making in Motion, exported it as ProRes 4444 with my project set to 32bpc and there was still banding. However, if you export as Animation from Motion or After Effects, there is no banding.