PAL Amiga – Which Mode to select? Benefits from 320*240 optim-Mode?

[uchristo]

Hey guys!

I’m trying to get my Amiga games (LoRes 320*256, Pixel Clock 7,09375MHz) working on OSSC. My goal is to achieve a output resolution of 1920*1080@50Hz with a centered image from source.
I’m currently testing with the titlescreen of Superfrog which seems to use the whole 256 lines from Amiga PAL loRes
The possibilities:

linemode x4
1.) Generic 4:3
Increase V.Active to 270 (4*256 = 1024 < 1080)
Increase H.Active to 1920(4*320 = 1280 < 1920)
Decrease V.Backporch to get an image of 1280*1024 which is centered in a 1080p-frame
2.) 320×240 optim.
Increase V.Active to 270
Increase H.Active to 480
>>> This does not work, have to stick on V.Active240 and H.Active320, but this truncates 16 lines, so it’s useless

linemode x5
5*256 = 1280 > 1080 >>>> too tall for 1080p (200 px)
5*320 = 1600 < 1920 >>>> this fits
The image would be truncated below the 216th Pixel from source, possible usable for some games but not compatible with all of them

I really don’t get the benefit from the HHHxVVV optimized modes (lx3 in 320*240 looks great, but the last 16 lines aren’t used and increasing V.Active seems to not do the trick). Will there be a 320×256 optimized mode at sometime? Or is this not necessary?

Edit: on lx4 320×240 optimized I think I forgot to increase H.Samplerate by 50% according to the increase of H.Active(320>480=50%+). I‘ll give it a try

[uchristo]

I changed the Sampling for 320x240L to H.Active 480, V.Active 270, H.Samplerate 681(454*1,5) and decreased V.Backporch. Them switched Output-Optiona for 288p to lx4 and mode for lx4 to 320×240 optimised and got a picture 🙂
Will now play with H.Samplerate fraction and Sampling Phase until the picture is solid

[uchristo]

I don’t get a stable image. Tried the same with my Wii. I set the output mode in Wii to 480i, chain it with YPbPr to GBS-controlled GBS8200 to downsample to 240p. I then linedouble 240p with 320*240 optimized lx4 mode on O.S.S.C.s’ AV3 input with H.Samplerate 427,75*1,5 = 640, H.Active=320*1,5=480, V.Active=270

On Wii I’m using 480i in 240pTestsuite and get a nearly(!) stable image with horizontal bars. These are not removable by adjusting H.Samplerate fraction and Sampling Phase. I also played with the filters for input and reverse LPF. No success until now.
What am I doing wrong?

[Harrumph]

Amiga optimal timings are all described in this thread:
Advanced timings for Amiga

I get what you’re trying to do with the 1.5 multiplier for widescreen, but it’s not the correct approach to optimally sample. With optimized mode you (nearly) always need to compromise with the AR of the source material.
Regarding the Wii, not sure how the Gbs-control downsample affects it (if it greatly oversamples, you may still be alright), but the Wii signal is always 858 dots (or 429 in 240p mode). Again, your approach does not improve on the signal compared to generic mode.

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