TV safe area

Shiru · Post by **Shiru** » Sat Sep 08, 2007 6:59 am

I wonder, how SMD picture look on average TV set? As far as I remember, in 320x224 PAL picture fullscreen horizontally, and has small borders in top and bottom parts (so picture really 'flattened', i.e. has ratio same as resolution, with square pixels). But I want to know, how 320x224 looks in NTSC and how 256x224 looks on both systems (is it have borders in left and right parts, or stretched to whole screen). I.e., must I assume that edge parts of picture may be offscreen on some TV sets, or there is no such problem.

Fonzie · Post by **Fonzie** » Sat Sep 08, 2007 10:53 am

320*224 = Fullscreen on NTSC system... = Borderline on PAL system.
320*240 = Sync error on NTSC system = Almost no top/bottom borders on PAL.

256 width = Same as 320 width (horizontally distorted).

However, some megadrive set just have a display shift of almost 16 pixels to the left... So you may loose 16 pixels on the left. So you may never put very important data there...

A devfriend told me that NTSC systems on old TV may cut a bit top and bottom of screen (like 5-6 pixels) too.

And just for a reminder.. the border color is controllable (especially important for PAL games). Just use the entry 0 of palette 0 (you can also customize the color to use in a vdp register).

TmEE co.(TM) · Post by **TmEE co.(TM)** » Sat Sep 08, 2007 1:43 pm

My TV shows nearly all the picture, but other TVs in my family show lot less.

Horizontally around 8 pixels left side are almost entirely hidden, in 256 mode even 10... and on right side you can see overscan.

Vertically in PAL you will always see all the pixels (with borders, around 16 pixels both), in NTSC you'll probably miss around 6 pixels form up and down...

My TV shows all the picture in all cases, all above is based on other TVs in my family...

I'd send you some pictures but I don't have a digicam anymore.

Jorge Nuno · Post by **Jorge Nuno** » Sat Sep 08, 2007 2:27 pm

I my TV's the picture is shifted to the left, using RGB, if you toggle to RF or composite video the picture will be centered horizontaly.

And the same happens with the playstation2:

Composite-> centered
RGB/YCbCr-> shifted left

I think, back then they did it because composite was very spread, so the sync was "delayed" to give some time to encode RGB in YIQ then in Svideo/composite...

... But I think, in MD if combining manually the Hsync and Vsync signals the picture will be centered (I hope so)

TmEE co.(TM) · Post by **TmEE co.(TM)** » Sat Sep 08, 2007 2:31 pm

I put in a custom Hsync and Vsync mixer into my MD to get exactly centered screen using RGB. I did similiar thing to my Dreamcast, but the picture is still shifted (but little less).

Jorge Nuno · Post by **Jorge Nuno** » Sat Sep 08, 2007 2:34 pm

TmEE co.(TM) wrote:I put in a custom Hsync and Vsync mixer into my MD to get exactly centered screen using RGB. I did similiar thing to my Dreamcast, but the picture is still shifted (but little less).

You XORed them? or it is something else?

I know the polarity of Csync and Vsync only, so I don't know what to do to mix V+H

TmEE co.(TM) · Post by **TmEE co.(TM)** » Sat Sep 08, 2007 2:42 pm

It's just two transistors and few resistors... and it was made 100% trial and error...

I'll make a schematic of it...

Jorge Nuno · Post by **Jorge Nuno** » Sat Sep 08, 2007 2:55 pm

Are those transistors BC548?

If it is true I think I don't need schematic...

TmEE co.(TM) · Post by **TmEE co.(TM)** » Sat Sep 08, 2007 3:02 pm

These are C945, got from a fried VGA monitor... I don't know if there is something like this... I'm about to scan the schematic... stay tuned

Jorge Nuno · Post by **Jorge Nuno** » Sat Sep 08, 2007 3:05 pm

LOL no rushes I'm going to the beach, I won't have time now...

I really thought they were bc548, becuase they are general purpose NPN, and very used (558 is the complementary PNP)

TmEE co.(TM) · Post by **TmEE co.(TM)** » Sat Sep 08, 2007 3:16 pm

Here it is (sorry for 150dpi) :

I'm 100% sure that any NPN will do...

Jorge Nuno · Post by **Jorge Nuno** » Sat Sep 08, 2007 3:25 pm

Yeah seems the bc548 will work, it supports more current than yours,
but the breakdown voltage is worse (30V), but it is still beyond TTL levels...

And the pinout is different too...

BTW I'm assuming Vsync enters from the left, right?

TmEE co.(TM) · Post by **TmEE co.(TM)** » Sat Sep 08, 2007 3:27 pm

Upper input is Hsync, Lower is Vsync... how did I miss it... doesn't matter... the most right side one is of course Csync.

This doesn't help with 256 resolutions... picture gets -slightly- distorted

8bitwizard · Post by **8bitwizard** » Sat Sep 08, 2007 6:05 pm

I've found that it's best to avoid using the top two and bottom two rows, and the left and right four columns on NTSC. That means keeping to 256x192 or 32x24 for anything important.

It's not that you shouldn't use anything outside that range (it lets you avoid having a blank border), but you can't count on anything outside that area being visible on an actual Genesis console and TV set. So don't put status displays or scores on the edges.

TmEE co.(TM) · Post by **TmEE co.(TM)** » Sat Sep 08, 2007 6:21 pm

Why all TVs won't show the whole screen ? My TV shows everything !!! I even have 8-pixels of vertical overscan in NTSC !!! And that is a PAL TV !!!