Welcome to TVPaint Community forums !

Hi Merciful Mentors,
I have searched through the topics and have not found my answer.
I am now making the settings to start my project and I decided to make my animation settings for a DCP. I am using 1998 x 1080, 24 fps, with the pixel aspect, square.
Then, when I opened my project in TVPP , I modified the pixel aspect to 1.85, which was my only modification. I noticed that that change to 1.85 adds a zero, making it 1.850 and the image is now weird looking.
It's not as tall. Am I wrong to change the aspect ratio from square, because I would love to have the bigger looking image size, but I really want to have the settings perfect for the DCP (Digital Cinema Package) Software. So far, I plan on using the Open Source DCP Software to make my DCP.
Thank you so much for your kind help.

I do my projects in standard HDTV, 1920 x 1080 square pixels, 25 fps. This was converted to DCP by a service here in Berlin, then projected on large screen. Perfect.

"Pixel aspect" in TVP really means the proportion of a single pixel, not the proportion of the film frame. Keep it 1:1 (square) and be happy.

From Wikipedia:

Maximum frame sizes are 2048×1080 for 2K DC, and 4096×2160 for 4K DC. Common formats are:
SMPTE (JPEG 2000)
Flat (1998×1080 or 3996×2160), ~1.85:1 aspect ratio
Scope (2048×858 or 4096×1716), ~2.39:1 aspect ratio
HDTV (1920×1080 or 3840×2160), 16:9 aspect ratio (~1.78:1) (although not specifically defined in the DCI specification, this resolution is DCI compliant per section 8.4.3.2).
Full (2048×1080 or 4096×2160) (~1.9:1 aspect ratio, official name by DCI is Full Container. Not widely accepted in cinemas.)

Thank you so much, Slow tiger, for your very helpful and very quick reply.
You guessed it, I am following the DCI guidelines for the flat 1998 x 1080, 24fps.

Thanks again for your help. I really appreciate it!

OK, some basics.

The "aspect ratio" of TVP has nothing to do with the "Aspect Ratio" of any screen format. (It only defines which kind of rectangle pixels you use if you don't use square pixels. But we always use square pixels in production. Don't change that 1:1 to anything else.)

The screen format so-called "aspect ratio" is just a result of your project's dimensions.
1920 x 1080 equals 1:1,78 equals 16:9.
1998 x 1080 equals 1:1,85.
In common projection settings these two formats are treated the same, since there's a black curtain around the screen which swallows some pixels left and right anyway. Festival application forms usually ask you to choose between 4:3 and 1:1,85, (and Scope, which would be 1:2,25, but your film is not in scope.)

You stay with 1998 x 1080 and square pixels, and the DCP software does its part. Don't worry about 8bit, your film will look nice.