Colour bars

[VRYK]

Two PGCs in the Title domain consist of vertical colour bars, presumably for calibration. Can they be blanked out ?

[r0lZ]

They are usually never shown junk, and can be blanked. But it is better to verify. Can you reach them when playing the DVD? Are there post-commands or NextPGCN links in the PGCs?

Anyway, they do not consume much more disc space than a blank frame, so IMO, it is useless to blank them.

[VRYK]

Thanks for your reply. They don’t show up during playback. In both PGCs there is a post-command calling the VMGM domain. There are also pre-commands setting gprm registers and a conditional link PGN command. Following your advice I shall not blank them. Apart from the negligible space aspect, can I take it as a rule that where there are pre- and/or post –commands, these PGCs serve a purpose and should not be blanked out ?
The same video sets subtitles on by default: (SetSTN) Set Sub-picture stream = 0, on. What purpose does this apparently self-conflicting setting serve? Simply clearing the On box in the Command Editor turned the subpics Off.

[r0lZ]

Apart from the negligible space aspect, can I take it as a rule that where there are pre- and/or post -commands, these PGCs serve a purpose and should not be blanked out ?

If there are post commands (or a non-zero NextPGCN link), that means that the video content of the PGC is *probably* played. In some cases, there is also a pre-command that jumps outside the PGC before the video playback, and if that command is not conditional and cannot be skipped by a conditional GoTo, then the post commands are useless, as the video content is never played. PgcEdit's Remove Useless Stuff function should be able to detect that kind of pseudo-dummy PGCs and blank them automatically.

In your case, the LinkPGN command indicates that at least some cells of the PGCs can be played, and PgcEdit should not blank the PGC automatically. You can of course blank it manually if you are sure you don't need it.

The same video sets subtitles on by default: (SetSTN) Set Sub-picture stream = 0, on. What purpose does this apparently self-conflicting setting serve? Simply clearing the On box in the Command Editor turned the subpics Off.

Set Sub-picture stream = 0, on is not a strange command. It selects the first subtitle track and enables it. (Don't forget that the track numbers are zero based.) Turning it off is potentially dangerous, unless you know what you are doing.

I have no idea why they use that command, as its effect depends of the next Title PGCs that will be played.

Note that in many commercial DVDs, the subpic track 0 is forced each time a menu is played (and the original subtitle track is restored before playing a Title again). I have never understood why. In the menu domains, the subpic track 0 contains the button highlights, and is always active, regardless of the SetSTN settings (that affect only the Title domains). So IMO, forcing subpic 0 to play a menu is useless. Maybe they do that as a workaround for bugs with menu buttons highlights in some players.

[VRYK]

Many thanks for your reply.

< Set Sub-picture stream = 0, on is not a strange command>
I confused the command with = mov(0).

The buttons in one of this video’s menus have no apparent highlight colour - neither when selected nor activated. I understand these settings are in the PCI element of the NAV Pack and could be changed in PgcEdit’s Colour Scheme Editor. However, since the www.mpucoder.com/DVD reference is above my head, I wonder if there is a simpler guide on how to handle this ?

[r0lZ]

You can easily define a translucent rectangle for the highlight with the colour scheme editor. Just assign the same colour and level of opacity to the four "selected" colours. Same thing for the activated colours, but select another colour and make the highlight more opaque. The rectangle will occupy the zone defined in the menu editor.

Note that the VOB must have a subpicture stream, even if it is blank, as otherwise, most players will not display the highlight, and some will not let you activate a button.

To define a more sophisticated highlight, you must draw it in the subpic stream. You can export the current subpic image with DVDSubEdit, edit it with any paint program, and import it back. There are many guides on how to do it, but usually, they explain how to add a new button highlight in a subpic image that contains already some highlights. However, if the menu PGC has no subpic, you're stuck. You will have to reauthor the menu to define the highlights, as DVDSubEdit can only replace the subpic with a new one. It cannot create a new subpic.

[VRYK]

This seems to be a bit of a queer case. In the Menu Buttons editor four buttons are visible – three languages and a fourth in the top left hand corner (button 4 - hidden?) with command LinkTopCell, button1, which latter is the English-language button. According to the PGC Editor there are 6 buttons ,but only one stream is listed. Does this mean that only one of the buttons could be edited without having to resort to re-authoring ? In the Domain “Streams” Attributes window it is unspecified – how can one identify which button this is?

[r0lZ]

The fourth button is hidden, that's right.

All button highlights are in the same subpic stream. Only the part of the subpic that is inside the button zone is visible when that button is selected or activated. The zones of the other buttons and the part of the screen that is not included in the button rectangles are hidden. (In fact, it's a bit more complex, but with almost all menus, it's how the highlights are handled.)

However, if the menu is in 16:9, two (or in some rare cases, 3) subpic streams are necessary, but they are grouped together under the same "track" in Domain Track Attributes. (The next version of PgcEdit will use the term Track instead of Stream, to reserve Stream to the real, physical streams included in the VOB files.) It's because different highlights are used when the menu is displayed on a 4:3 or on a 16:9 TV. So, if you want to edit a 16:9 menu with DVDSubEdit, don't forget to edit it in the two (or 3) possible display modes.

[VRYK]

Many thanks for bearing with me. I am still trying to clear my thoughts on button colours.

The PgcEdit Manual states that “The button highlights are defined in the sub-picture streams of the menu. Each pixel in the sub-pic data may be assigned one of 4 values. – these are called Background, Pattern, Emphasis 1 and Emphasis 2 ….”.

This passage, which concerns only the button’s highlights, means that individual pixels can be edited. The continuation of the text concerns the button as a whole.

While the concept of background colour seems clear, I don’t understand the other elements (Pattern and Emphasis). A button’s outline colour when selected in PgcEdit’s Menu button’s window seems always to be green and when not selected red. Are these the Pattern colours? Also, I have not found an explanation of Emphasis 1 and Emphasis2.

In DVDSubEdit how does one know which status is displayed when cycling through with Ctrl-q (in fact there seem to be three states (not just Selected and Activated).

[r0lZ]

B, P, E1 and E2 are just labels arbitrarily assigned to the four subpic colour indexes. They have absolutely no meaning, although it is recommended to use B (colour 0) for the transparent background, P (c 1) for the main color, and E1 (c 2) and E2 (c 3) for the antialiasing or second and third visible colours. Just remember that a subpic can use a maximum of 4 colours, at least one of them being usually fully transparent.

Each subpic is a 2-bits image. That means that when you draw an image to import it later in a subpic, you can use only 4 colours. But the colours used in your paint program are not the colours you will see in the subpic. The background colour has the value 0, P has value 1, and E1 and E2 values 2 and 3. When the image is converted to be included in the subpic stream (for example by DVDSubEdit), it is converted to the 2-bit image and compacted (using RLE compression) in the subpic stream. (The colours you have used when drawing the image are discarded, as the image has no color table when it is stored in the subpic.)

When the player displays a button highlight, it looks at the value of each pixel, and use it as an index in the colour scheme. For example, if the pixel has value 1, it uses the colour scheme's Pattern definition to determine the index in the CLUT (Colour LookUp Table) and the level of opacity. The CLUT index is the position of the colour in the colour table defined in the PGC. You can edit the CLUT index and the level of opacity for the 4 pixel types with the colour scheme editor, and you can edit the colour that will finally be displayed in the PGC Editor.

So, to summarize, the pixel is converted to an index to determine the colour type to use in the colour scheme, and the colour scheme's colour index is then converted to the corresponding colour in the CLUT of the PGC.

It may seems unnecessary to use an index to another index to a colour, but it's how it works! (An advantage of not storing the colour directly in the colour scheme is that the same cell can have different button colours if it is reused in different PGCs, as you can freely change the CLUT colours of the PGCs individually.)

Note that there are 3 colour schemes available (schemes 1, 2 and 3). You can freely assign any colour scheme to a specific button highlight. That means that you can use different colours and opacity values for the different buttons of a menu. (Of course, if there are more than 3 buttons, some of them will have to share the same scheme.) These 3 schemes are stored in the Nav Packs of the VOBs.

In addition to these 3 colour schemes, there is another scheme that is stored in the subpic stream itself (scheme 0, not editable in PgcEdit, but editable in DVDSubEdit). That scheme is used for standard subtitles, and for the area of the image that is not covered by the currently selected or activated button. (It has no "selected" and "activated" modes: just a single mode.) In menus, it is usually fully transparent (as you don't want to see highlights over the buttons that are not currently current, or over the whole background). For normal subtitles, it is used to render the subtitle.

DVDSubEdit shows you the colour scheme of a specific button in selected, activated and not selected/activated modes. In other words, when it shows the selected mode, it use the "selected" part of the colour scheme assigned to the button, and similarly for the activated mode. The third mode shows you the colour scheme 0, that is used by that particular button when another button is selected or activated, and for the whole background.

[VRYK]

Many thanks for your exhaustive reply – I now have a lot of “pain sur la planche” to digest!