Subpictures: PAL->NTSC and vice versa?

[Matthew]

Lets say I have fullscreen subtitle bmps ready for import into Maestro/Scenarist, but the bmps are NTSC when I want them to be PAL, or vice versa. What's the correct way of dealing with this?

i.e. 720 x 478 (NTSC) -> 720 x 574 (PAL)
i.e. 720 x 574 (PAL) -> 720 x 478 (NTSC)

Now, I know I can just resize them but that will result in the aspect ratio being off? Do I instead need to increase/crop the image size (evenly on top/bottom) without touching the area where the subs are displayed?

BTW editing the details/timecodes in the son/sst file(s) is something I already have (mostly) sorted ;)

Thanks :)

[DaRat]

I usualy use a very simple PS action, like copy, open new (720x576), paste, move to bottom (in the most cases this will fit it just right above the 5% overscan area), fill the rest with bgcolor, convert to indexed and save as bmp.

[Matthew]

Thanks for the reply.

In other words it's a case of cropping or adding 96 pixels to the top. After posting I compared some NTSC and PAL bitmaps and came to this conclusion.

PAL->NTSC is easy as subrip can be used to crop the bmps (plus a slight adjustment to the son/sst may be required). However, for NTSC->PAL the bmps will be undersized. As far as Maestro goes, this can be dealt with by editing a couple of values in the son file, but Scenarist seems to only support full screen bitmaps. So increasing the canvas size of each image would be required if I wanted to use Scenarist.

Now doing what you suggest is fine for a few subpictures, but not over 1000 :\

I'll have a look into batch processing, but given it's not a case of straight resizing (which would be easy) but rather increasing the canvas size, I'm not optimistic.

edit: created a droplet in Photoshop and "dropletname.exe X:\folder\subs" seems to do the trick.

[Matthew]

mmmm...I'm sure nobody cares, but after actually testing using PowerDVD, it is resizing not canvas increase or crop that is required for subtitle bmps (so subrip provides incorrect results for PAL->NTSC). Just changing the canvas size results in incorrectly positioned subtitles, compared to the original.

Doesn't make much difference on a practical level, I just created 2 new Photoshop droplets.

[MvB]

Just cropping is not right. NTSC uses the same aspect ratio, but with fewer lines an more space between the lines. So a resize would be appropriate.

[SomeJoe]

The problem with a resize is that the subpictures are only 2 bits per pixel, thus only 4 colors. Typically, the text has been rendered from a TrueType font with no anti-aliasing. If you resize and allow Photoshop to anti-alias, the resulting picture is then way more than 2 bits per pixel. If you resize without allowing anti-aliasing, the resulting text will be very jagged, because it hasn't been rendered at that particular size.

Cropping and/or changing the canvas size, while maintaining the text's relative position on the screen is the way to go. The only side effects this causes is that 1) the text will be slightly stretched or compressed horizontally, depending on whether the conversion was PAL->NTSC or NTSC->PAL due to the difference in pixel aspect ratio, and 2) the text will be made slightly larger or smaller due to the difference in the number of horizontal scanlines. On most fonts, these changes don't make a huge difference, although PAL->NTSC with a font that was already pretty narrow or large, or NTSC->PAL with a font that was already wide or small may be objectionable.

[Matthew]

Thanks for the reply SomeJoe.

I tried a couple of small NTSC->PAL test conversions and in powerdvd the subs do look a little jagged, however this is not noticeable on a television. The subs do seem to shimmer/shake more though on a tv.

But the initial results do seem okay.