zgv - picture viewer for VGA/SVGA displays Linux Man Page

ZGV (1) manpage

ZGV

30th June 2003

Version 5.7

Graphics Software

NAME
SYNOPSIS
DESCRIPTION
ACKNOWLEDGEMENTS
OPTIONS
ONLINE HELP
THE FILE SELECTOR
EXITING ZGV
THUMBNAILS
SCREEN LAYOUT
MOVING AROUND THE LIST

There are many commands for moving the cursor. In summary, most `special' keys like the cursors do what you'd imagine they do --- also, a few Emacs-like keys, a few vi-like keys, and the Sinclair Spectrum-style (!) QAOP keys are supported.

Using a mouse in the file selector is not covered here. See Mouse Funcs in the File Selector, for details of what you can do with a mouse. (Experienced users may wish to consult the Tom & Jerry and Pinky and the Brain cartoons for further enlightenment on this subject.)

`Cursor Up'

`^P'

`k'

`q'

Move up. Moving up from a topmost entry moves to the bottom of the previous column.

`Cursor Down'

`^N'

`j'

`a'

Move down. Moving down from a bottommost entry moves to the top of the next column.

`Cursor Left'

`^B'

`h'

`o'

Move left one column.

`Cursor Right'

`^F'

`l'

`p'

Move right one column.

`Page Up'

`^U'

Move the cursor back (nearly) a page.

`Page Down'

`^V'

Move the cursor forward (nearly) a page.

`Home'

`^A'

Move the cursor to the start of the list.

`End'

`^E'

Move the cursor to the end of the list.

`g'

`''

Move the cursor to the first filename starting with the next key pressed, which would generally be a letter or number. Case is significant; `a' and `A' are different.

If no files start with the specified character, it moves to the first file which starts with a later char (in asciibetical order). If there are none for which this is the case, it moves to the last file --- unless there are no files (just directories), in which case it has no effect.

VIEWING A FILE

Enter

' when you've moved the cursor to the file to view. However, you can also view tagged files as a `slideshow', which is described later (see

Tagging

Enter

View a picture file, or if the cursor is on a subdirectory, make that the current directory. A progress indicator is shown when reading in a file --- while this is onscreen, you can use `Esc' to abort.

DIALOG BOXES

Enter

' or `

Esc

' (if using a mouse, clicking

has the same effect).

Getting a yes or no answer. `

Enter

' or `

' picks `yes'; `

Esc

' or `

' picks no. (Again, you can click on the relevant button with the mouse to do the same.)

Reading a directory name. Here you should type the directory name then `

Enter

', or press `

Esc

' to abort. In fact, this line-input dialog allows a certain amount of editing, and so supports these additional keys:

Cursor Left

`^B'

Move the cursor left. (An underline character shows the cursor position.)

`Cursor Right'

`^F'

Move the cursor right.

`Home'

`^A'

Move the cursor to the start of the line.

`End'

`^E'

Move the cursor to the end of the line.

`Insert'

`^I'

Toggle insert/overwrite mode. (Insert mode is the default.) In insert mode, characters you type are inserted at the cursor position. In overwrite mode, they replace the existing chars.

`Backspace'

`^H'

Delete char to the left of the cursor. (This assumes `Backspace' really generates a `DEL', which is the usual setup on Linux. Note that `Backspace' is (usually) the key above the main `Enter' key; it is often labelled simply as an arrow.)

`Delete'

`^D'

Delete the char the cursor is on.

TAGGING

Configuring zgv

, if you'd prefer zgv to use different colours.)

"Tag and Untag Commands"

' (unshifted `

') command has quite a different effect to that of `

' (shifted `

').

Changing Picture

, for details.

Tag file.

`n'

Untag file. Note that this is `n' (for `no tag', er, or something like that); `u' would be more logical, but that is used for updating thumbnails.

`T'

Tag all files.

`N'

Untag all files. This is on `N' rather than `U' for consistency.

`Space'

Toggle the tag status of the file --- if it's tagged, untag it; if it's untagged, tag it.

To see how many files are tagged, use `Alt-f' (see Other File Sel Commands).

"Slideshows" A `slideshow' lets you view all the tagged files in the current directory one after the other, or in a randomised order if `shuffling' is enabled (see File Selector Toggles):

`Tab'

View the tagged files as a slideshow. (`Tab' is usually the key above `Caps Lock', which is often labelled with two arrows.)

Each file is shown for a certain amount of time, normally 4 seconds. (See Options, if you find this too short or long.) After the time runs out, the next file is shown. You can cut this delay short by hand using one of the viewer's change-picture commands such as `Space' (see Changing Picture), or abort the slideshow prematurely by pressing `Esc'. You can also pause a slideshow so that you remain on the current file until you unpause it (see Pausing Slideshows).

Normally, once each file has been shown the slideshow ends, and you are returned to the file selector. But if looping is enabled, the slideshow repeats until you press `Esc' (see File Selector Toggles).

"Copying/Moving/Deleting Files" You can copy or move tagged files to a directory you specify, or delete all tagged files. If no files are tagged, zgv copies/moves/deletes the file the cursor is currently on --- unless the cursor is on a subdirectory, in which case it gives an error.

Note that the commands given here are uppercase --- lowercase `c', `m', and `d' do not do the same thing.

`C'

Copy tagged files (or the current file) to a given directory. zgv asks for the destination directory using a dialog (see Dialog Boxes) and copies the files there. If it comes to copy a file but there is an existing file in the dir with the same name, the file is not copied and nor are any of the remaining files.

`M'

Move tagged files (or the current file) similarly.

`D'

Delete tagged files (or the current file) similarly. In this case, there's obviously no need to specify any directory :-) but you're prompted before deletion starts (unless this is disabled, see Configuring zgv). It also deletes thumbnails, for those files which have them.

RENAMING A FILE

`Alt-r'

Rename the current file or directory --- zgv will refuse to overwrite any existing files/directories. The new name must remain in the current directory. (See Copying/Moving/Deleting Files, for how to move a file to a different directory (albeit keeping the same name).)

It's better to use `R' than `Alt-r'; the latter never made much sense, and is likely to be removed before long.

CHANGING DIRECTORY

Enter

'. (Selecting `

(..)

' moves to the parent directory of the current one.)

', not `

'.)

Go to a specified directory. zgv asks for the destination directory using a dialog box which you should type the dir's name into (see Dialog Boxes), and moves to that directory if it exists.

If the directory turns out to be unreadable --- i.e. you do not have permission to read it --- zgv resorts to going to your home directory. (This is actually a general mechanism in zgv, but this command is the most likely trigger of it.) If that in turn is unreadable, zgv gives up in disgust and exits. :-)

CHANGING THE SORTING ORDER

Alt-n

Sort by name. This is the default.

`Alt-s'

Sort by size. The biggest files are listed last.

`Alt-d'

`Alt-t'

Sort by last-modified date/time. The newest files are listed last.

`Alt-e'

Sort by extension.

FILE SELECTOR TOGGLES

Options

) and/or config file settings (see

Configuring zgv

Toggle display of thumbnails (default is on). The without-thumbnails display can sometimes be useful for navigating around large directories (many filenames are shown onscreen at once), and it is of course faster.

`s'

Toggle scrollbar on/off (default is on). The scrollbar shows which part and which proportion of the list is currently being shown onscreen, and when mouse support is enabled can be used to move around the list.

`S'

Toggle shuffling (randomising) of slideshows. See Slideshows.

`L'

Toggle looping in slideshows. See Slideshows.

`Alt-m'

Toggle use of `magic numbers' (identifiers at the start of a file) to pick which files in a directory to list in the selector. The usual method of doing this is based on the file's extension (see File Type Identification, which is much faster but won't catch e.g. files without extensions.

`c'

If the file selector is running in 16-colour mode (it usually doesn't unless zgv has no choice --- see 16-colour File Selector), toggle between greyscale (default) and colour thumbnails.

OTHER FILE SEL COMMANDS

Delete

Delete (only) the file the cursor is on. Asks for confirmation (unless this is disabled, see Configuring zgv). It also deletes the file's thumbnail, if it has one. See Copying/Moving/Deleting Files, for a more general command which deletes all tagged files.

`:'

Show various details about the file the cursor is on; the (full) filename, the size in kilobytes, width/height if recorded in any thumbnail, last-modified date, etc. You can also use the `;' key to get this.

`Alt-f'

Show the number of (picture) files in the current directory, and the number of tagged files (see Tagging).

`^L'

`^R'

Rescan the directory contents, and redraw the screen.

`K'

Kill mouse --- disable mouse for the rest of this zgv session. (It prompts to check if you really want to do so.) This can be useful if you have the mouse enabled in a config file, so that zgv always starts up with the mouse on, but you're currently using just the keyboard. In such a situation the mouse pointer can be a bit annoying. This command lets you disable the mouse completely for the current zgv process.

SHOWING MORE FILES

'). This keeps the selector running at a reasonable speed even on relatively slow machines.

Video Modes

), you may want to see more thumbnails onscreen at once.

Select 640x480 mode. This is the default.

`F2'

Select 800x600 mode.

`F3'

Select 1024x768 mode.

`F4'

Select 1280x1024 mode.

If you want to change the default mode used in the file selector, use the fs-start-mode config file setting (see Configuring zgv). For example, to use 800x600 by default, you'd use fs-start-mode 800 600 8.

Note these modes are subject to the same checks as in the viewer --- in particular, this means that the file selector obeys the viewer's mode-good, mode-bad, etc. settings. See Config Variables.

Finally, if you have no 640x480 256-colour mode, or if force-fs-16col has been set, the 640x480 16-colour mode is all that is available.

16-COLOUR FILE SELECTOR

' to toggle between the two, or set zgv up to default to using colour thumbnails instead with

fs-16col-colour-thumbnails on

in a config file (see

Configuring zgv

--force-fs-16col

option.)

THE VIEWER

EXITING THE VIEWER

Esc

`x'

Exit the viewer.

If you got to the viewer from the file selector, you're returned there; if you bypassed the file selector (by running zgv with a file (or files) to view specified on the command-line --- see Options) then exiting the viewer also exits zgv.

BIG PICTURES

Video Modes

), either manually or by using auto-mode-fit.

Supported File Formats

).)

"Scrolling"

Cursor Up

`K'

`Q'

Move up 100 pixels. `k' and `q' move up 10 pixels.

`Cursor Down'

`J'

`A'

Move down 100 pixels. `j' and `a' move down 10 pixels.

`Cursor Left'

`H'

`O'

Move left 100 pixels. `h' and `o' move left 10 pixels.

`Cursor Right'

`L'

`P'

Move right 100 pixels. `l' and `p' move right 10 pixels.

`Page Up'

`^U'

Move up (nearly) a screenful. (It moves 90% of the screen height.)

`Page Down'

`^V'

Move down (nearly) a screenful.

`-'

Move left (nearly) a screenful. (It moves 90% of the screen width.)

`='

Move right (nearly) a screenful.

`Home'

`^A'

Move to the top-left of the picture.

`End'

`^E'

Move to the bottom-right of the picture.

"Zoom Mode" An alternative way of viewing the whole picture, one which lets you see the picture onscreen all at once no matter how big (or small) it is, is zoom mode.

Zoom mode's name derives from the idea of `zooming' a small file up to fit the screen. But in reality, it is more often used to reduce a large file to fit the screen.

Zoom mode is not the default, and has to be enabled. Once enabled, it stays on until you turn it off again.

By default, the way zoom mode reduces a file to fit the screen is (relatively) quick but harsh, and may make the picture look ugly. Enabling vkludge smoothes the picture, giving a better and more accurate result, but takes longer. It too is not the default, but stays on until turned off again.

`z'

Toggle zoom mode.

`Alt-r'

When in zoom mode, only reduce pictures to fit. This can be useful when going through a lot of unpredictably-sized pictures, as it means that you can see all of a big picture easily without also meaning that tiny little icons assume a scale of Biblical proportions. :-)

`v'

Toggle vkludge, which enables appropriate smoothing when zoom mode is reducing a picture to fit the screen. It also enables similar smoothing for non-zoomed pictures in 320x400x8 and 360x480x8 modes. See Virtual Modes.

`n'

Resume `normal' display --- disables zoom mode (and scaling mode).

"Auto-mode-fit" If it seems strange to you to use scrolling or zoom mode to see the whole picture when you could just use a different video mode (to change the size of the pixels displayed onscreen), you may find auto-mode-fit useful.

If enabled, and when a picture is loaded, the current mode is automatically switched to the `smallest' mode which is both wider and taller than the picture is (or of equal width/height). In other words, the (theoretically) most appropriate mode. If no mode can fit the picture onscreen, the `largest' mode is chosen.

Auto-mode-fit is not the default, so you have to enable it if you want to use it.

`Z'

Toggle auto-mode-fit mode. Usually this only takes effect when a picture is loaded (so that manual mode switching still works), but when you enable it zgv does a one-off auto-mode-fit on the current picture. (Note also that disabling it leaves you in the current mode, so that has no obvious effect; for this reason, the picture is redrawn (as a visual cue that you haven't just been ignored :-)).)

I should point out that all the mode-switching can be a bit hard on your monitor, so even if you really like this option you might not want to enable it all the time (e.g. in a config file), but instead only turn it on when you `need' it. Still, it's up to you.

Certain modes are excluded from those chosen by auto-mode-fit. In particular, no 320x200 mode is ever chosen, nor is 320x400x8. These exceptions are made due to the unusual aspect ratio. 640x480x4 is excluded due to the slightly odd way it works, which makes it ill-suited to automatic selection. 360x480x8 is considered, despite the aspect ratio, if no 640x480x8 mode exists.

SCALING

Increase the ratio by adding one --- this leads to ratios of 2:1, 3:1, 4:1...

`d'

Increase the ratio by doubling it --- leads to ratios of 2:1, 4:1, 8:1...

Usually `d' is more useful.

There are similar commands to decrease the ratio (when it reaches 1:1 scaling is disabled):

`S'

Decrease the ratio by subtracting one.

`D'

Decrease the ratio by halving it.

The scaling ratio is never decreased below 1:1. It is also never increased beyond 512:1, where zgv stops so that pixels may be conserved for future generations. :-)

You can undo the effect of scaling at any time by using `n' (which also disables zoom mode).

Normally, scaling works by simply making the pixels into larger and larger squares (in effect), which remain the same colour. However, if you are using a 15/16/24/32-bit mode (see Video Modes), you can enable a feature called `interpolation' which smoothly graduates the colour change between the top-left corners of each pixel. This is very slow, but looks nice.

`i'

Toggle interpolation in scaling mode.

`!'

Toggle off-by-one interpolation (disabled by default). Using this off-by-one method gives incorrect results, but this can occasionally be useful at ratios of 2:1 and 3:1 for relatively low-quality JPEGs.

(If you like the appearance of scaling with interpolation, you may also be interested in a program I wrote called pnminterp, which can scale up a PGM or PPM file while applying this effect.)

MIRROR AND ROTATE

`Mirror' the picture (flip it horizontally).

`f'

`Flip' the picture (flip it vertically).

`r'

Rotate the picture 90 degrees clockwise.

`R'

Rotate the picture 90 degrees anti-clockwise. (This is a little slower as it works by effectively doing `r' then `f' then `m'.)

`Alt-n'

Restore the picture orientation to normal. This undoes the effect of any mirrors, flips, and/or rotations.

zgv normally reverts the picture orientation (the way the picture has been transformed by mirror/flip/rotate) back to normal when you view a new picture. However, there are various ways you can retain the orientation between pictures, so that the new picture is mirrored, flipped, and/or rotated in the same way. Here are two of the ways:

`Alt-o'

Re-use the previous picture's orientation for this picture.

`Alt-s'

Save the current picture orientation, making all pictures viewed until you press `Esc' use it. (The orientation reverts to normal after that, though.)

Finally, you can choose to have the orientation preserved the whole time. To do this, put revert-orient off in a config file (see Configuring zgv).

BRIGHTNESS AND CONTRAST

Video Modes

Decrease contrast.

`.'

Increase contrast.

`<'

Decrease brightness.

`>'

Increase brightness.

`;'

Reset contrast and brightness to normal. (`*' is also supported, for hysterical raisins.)

Any contrast change is applied before any brightness change by default. However, you can reverse the order easily enough:

`B'

Reverse the order in which brightness and contrast are applied.

The order they're applied in does make a difference --- assuming you've modified both brightness and contrast, of course. :-) The normal order simply means you have a increased-contrast image which you change the brightness of. Obviously then, the reverse order reverses this, but it has the additional effect of changing the point around which contrast is applied.

GAMMA ADJUSTMENT

that

in a remotely sane fashion?

very

easy and fast to change gamma adjustment to commonly-required values. So here's how to do it:

Set gamma adjustment to 1.0, i.e. no adjustment. This is the default setting.

`2'

Set gamma adjustment to 2.2. This is useful for viewing linear-gamma files (one classic example being raytracer output) on an average PC monitor.

`3'

Set gamma adjustment to 1 divided by 2.2, i.e. roughly 0.45. This is useful for the reverse --- viewing average-PC-monitor-gamma files on a linear-gamma display. Historically I believe the classic example would have been viewing PC files on a Mac, but I don't know how true that is these days.

`4'

Set gamma adjustment to its initial value, as specified by a `-G' command-line option (see Options) or gamma config file setting (see Configuring zgv). The default value used if none was specified is 1.0.

A brief clarification is probably in order. The gamma adjustment value which you set in zgv is actually inverted from (i.e. one divided by) the true adjustment value used. This is (believe it or not :-)) intended to avoid confusion by reflecting the fact that screen gamma is the one most widely considered/well known.

You can also tweak the adjustment more precisely, in a similar way to brightness/contrast:

`Alt-,'

Decrease gamma adjustment (divide it by 1.05).

`Alt-.'

Increase gamma adjustment (multiply it by 1.05).

Note that `;', and the other keys which reset the brightness/contrast, deliberately avoid resetting the gamma adjustment.

INCREASED GREYSCALES

Video Modes

). Due to a limitation of the original VGA cards, these can have a maximum of 64 greyscales. This can give noticeable `edges' in some pictures.

Toggle whether to fake some extra greyscales/colours in 8-bit modes.

To disable it by default, put fake-cols off in a config file (see Configuring zgv).

CHANGING PICTURE

' and `

') temporarily returns to the file selector and shows the usual progress indicator while it's being read.

Dialog Boxes

, to see what `

Backspace

' is being used to mean here.)

Backspace

View previous file in dir, without progress indicator. (In slideshow, move to next file without waiting.)

`Enter'

View next file in dir, without progress indicator. (In slideshow, move to next file without waiting.)

`Space'

Tag current file, then view next file in dir, without progress indicator. (In slideshow, move to next file without waiting; it has no tagging effect during a slideshow.)

`^P'

View previous file in dir, with progress indicator. (In slideshow, acts like `Esc'.)

`^N'

View next file in dir, with progress indicator. (In slideshow, acts like `Esc'.)

Note that `Space' tags the file, rather than toggling the tag status as it does in the file selector. This mismatch is unfortunate, but in the viewer context the always-tag function is more likely to be what you'd want, since you can't see the file selector to see which files are tagged.

FILE DETAILS

Show file details, including such things as the filename, size, and width/height. This is almost identical to the equivalent command in the selector (see Other File Sel Commands); the only difference is that you can't use `;' to get this in the viewer, and the viewer doesn't depend on thumbnails for the width/height info.

PAUSING SLIDESHOWS

Pause slideshow, leaving you on the current image until you resume. You can still abort early with `Esc', go to the next image with `Enter', or in fact use any viewer commands at all.

`^Q'

Resume slideshow. If the timer has already run out (it keeps running while paused), this will go straight to the next image without any further delay, other than that needed to read the new picture.

The analogy with XON/XOFF isn't really that close --- for example, it's worth noting that when the slideshow is `paused', you can actually do anything you normally might in the viewer.

MULTIPLE-IMAGE GIF ANIMATION

-A

' or `

--auto-animate

' command-line option. See

Invoking zgv

Enter animation mode. (I don't know what the `e' stands for either. :-)) In this mode the normal viewer keys have no effect, and instead, a more limited set of keys are supported:

`Esc'

Stop the animation and return to the viewer. If auto-animation mode is enabled, it exits the viewer too.

`p'

Pause (or unpause) the animation.

`n'

Skip to the next frame. Generally only useful when paused.

If auto-animation is enabled, the `Backspace', `Enter', and `Space' keys do the same as they do in the normal viewer (see Changing Picture). Otherwise they act the same as `Esc'.

VIDEO MODES

"What a Video Mode is"

width

height

depth

is often used by zgv and this documentation. But here the `depth' is given in bits. This usage, while compact, probably makes more sense to programmers than to anyone else. Here's a list showing which `bit depths' match which number of colours:

4-bit means 16 colours.

8-bit means 256 colours.

15-bit means 32768 colours.

16-bit means 65536 colours.

24-bit means 16777216 colours (over 16 million).

32-bit means 16777216 colours too (!), since only 24 of the 32 bits are used for display purposes.

From the number of colours available in the latter modes, you can see why a bit depth notation is so useful!

So, in the widthxheightxdepth notation, our 640x480 256-colour mode would be 640x480x8, a 16-colour mode of the same size would be 640x480x4, and an equivalent `true-colour' (24-bit) mode would be 640x480x24.

Whenever you see a mode referred to as xxyxz in zgv or in this documentation, it is always specifying a video mode in this notation.

"Video Mode Issues" The obvious implication of differing video modes is that modes with more pixels horizontally and vertically will have smaller pixels, and so be able to show more of large pictures. The reverse (bigger pixels, making small pictures appear large) is not as important a consideration, as zgv can achieve much the same effect with scaling (see Scaling). Using video modes to do it is faster, but usually less convenient.

A more subtle, but much more important, implication of differing modes is related to the colour depth. More precisely, it's due to the differing ways the actual colours shown onscreen are obtained. In 15, 16, and 24/32-bit modes, the colour is specified `directly'; in 8-bit modes, a pixel's `colour' is really a number which selects one of 256 different colours to show. The overhead of translating from 8-bit to 15/16/24/32-bit is relatively minor, but in the 15/16/24/32-bit to 8-bit direction, it's considerable.

For this reason, and since converting from 24-bit to 15/16/32-bit is very easy, when zgv reads a picture it stores it in memory in one of two internal formats --- either as 8-bit, or as 24-bit. See File Format Depths, for discussion on which format zgv uses for which files.

But what difference does all this make when you're using zgv? Well, here's the bottom line:

o A file loaded as 8-bit can only ever display in 8-bit modes. Trying to choose a 15/16/24/32-bit mode will have no effect.

o A file loaded as 24-bit will only display in 15/16/24/32-bit modes, unless you have no 15/16/24/32-bit modes, in which case it will be dithered when it is read in. (But the config file setting force-viewer-8bit can be enabled to force the dithering behaviour. See Configuring zgv.)

o zgv normally remembers the last mode you switched to (the initial mode is usually 640x480x8), and keeps using that until you specify another to use. However, it will automatically choose the most similar 15/16/24/32-bit mode for a 24-bit file if the last mode was 8-bit, and vice versa.

Confused? Head hurting? Don't worry, it happens to the best of us. Especially where zgv is concerned. :-) Just play around with zgv for a while, and come back to this later on. It may make more sense after you've got a feel for what's going on.

"Default Video Mode" zgv using the last mode you selected is all very well, but that doesn't explain what happens if you've not chosen one. What happens is that it uses the default video mode.

The default mode is (unless you change it) the 640x480x8 mode. If this is not available or has been disabled, zgv defaults to 360x480x8 --- if this in turn is not available or has been disabled, it uses 320x200x8.

"Selecting a Video Mode" There are many different video modes supported by svgalib, and zgv lets you use most of them. To do so, it reserves many different keys for selecting video modes. These largely fall into four groups:

- The original VGA modes. These are on the number keys for historical reasons. (The reason being, the number keys exactly matched the mode numbers used by the old VGAlib.)

- The first group of SVGA modes. These are on the function keys `F1' to `F10'. These are generally the first modes to try, if you have them.

- The second group of SVGA modes. These are on the shifted function keys, here represented as `SF1', `SF2', and so on. (The first two of these are also available on `F11' and `F12'.) Not all of the shifted function keys are currently used by zgv.

- The third group of SVGA modes. These are again on unshifted function keys, but you must press `Tab' before pressing the function key --- i.e. press `Tab', let go, then press the function key. These are shown below as `Tab-F1', `Tab-F2', etc.

There are also the `[' and `]' keys, which select the next smaller/bigger mode. These are especially useful if you don't happen to have a spare lifetime in which to learn the `normal' mode-selecting keys. :-)

So, here's the list of mode-related commands:

`/'

List which key combination selects which video mode.

`['

Select the next smaller (lower-res) mode.

`]'

Select the next bigger (higher-res) mode. Both these mode-changing keys have the limits on modes selected that auto-mode-fit has (see Auto-mode-fit).

`0'

Select 640x480x4 mode. This emulates an 8-bit mode. See The Viewer 640x480x4 Mode.

`5'

Select 320x200x8 mode.

`6'

Select 320x240x8 mode.

`^'

Select 320x240x24 mode. (`^' is often on shift-6.)

`7'

Select 320x400x8 mode. This emulates a 640x400 mode. See Virtual Modes.

`8'

Select 360x480x8 mode. This emulates a 720x480 mode. See Virtual Modes.

`F1'

Select 640x480x8 mode.

`F2'

Select 800x600x8 mode.

`F3'

Select 1024x768x8 mode.

`F4'

Select 1280x1024x8 mode.

`F5'

Select 320x200x15 mode.

`F6'

Select 320x200x16 mode.

`F7'

Select 320x200x24 mode.

`F8'

Select 640x480x15 mode.

`F9'

Select 640x480x16 mode.

`F10'

Select 640x480x24 mode.

`SF1'

`F11'

Select 800x600x15 mode.

`SF2'

`F12'

Select 800x600x16 mode.

`SF3'

Select 800x600x24 mode.

`SF4'

Select 1024x768x15 mode.

`SF5'

Select 1024x768x16 mode.

`SF6'

Select 1024x768x24 mode.

`SF7'

Select 1280x1024x15 mode.

`SF8'

Select 1280x1024x16 mode.

`Tab-F1'

Select 1280x1024x24 mode.

`Tab-F2'

Select 1152x864x8 mode.

`Tab-F3'

Select 1152x864x15 mode.

`Tab-F4'

Select 1152x864x16 mode.

`Tab-F5'

Select 1152x864x24 mode.

`Tab-F6'

Select 1600x1200x8 mode.

`Tab-F7'

Select 1600x1200x15 mode.

`Tab-F8'

Select 1600x1200x16 mode.

`Tab-F9'

Select 1600x1200x24 mode.

"Special Modes" Normally, each pixel in the image is written more-or-less directly to the screen from zgv's internal copy of the picture (unless zoom mode and/or scaling have been enabled). However, there are three modes where zgv does things differently to make the modes more useful.

(These are mainly intended for users with only the original VGA modes available.)

"Virtual Modes" The original VGA hardware only had one `official' 256-colour mode, the 320x200 one. But it could be reprogrammed to allow other useful modes (known as `mode-X' modes) --- the ones svgalib provides are 320x240, 320x400, and 360x480.

These modes are available on all VGA cards. However, it's possible (perhaps even likely?) that some non-CRT displays may not be able to cope with them. All monitors should, though, even ordinary VGA monitors.

Now, while 320x240 is a nice sensible mode and can be used directly, 320x400 and 360x480 have very wide pixels. To deal with this, in these latter modes zgv maps every two pixels horizontally to one pixel onscreen. (Hence `virtual modes' --- physically they are 320x400 and 360x480, but in zgv they are virtual 640x400 and 720x480 modes.) This means that you still get a reasonable aspect ratio, one similar to (though not quite the same as) most other modes.

This raises the question of how this mapping is done. The normal approach is the quickest, but is very crude --- zgv simply uses the leftmost pixel of the two, and completely ignores the rightmost one. But if vkludge mode is enabled (see Zoom Mode), zgv will average the pixels' colours together and use the closest match available in the picture's palette. This usually gives a better result, but is considerably slower.

"The Viewer 640x480x4 Mode" As well as the non-standard VGA modes, zgv allows you to use the 640x480x4 (16-colour) VGA mode as if it were an 8-bit mode. (Pressing `0' selects this mode.) As with the file selector's 16-colour mode, it can work either in greyscale (the default) or in colour.

`c'

If in 640x480x4 mode, toggle between greyscale and colour.

In greyscale mode, the picture is displayed using 16 greyscale levels dithered to give the appearance of 61. In colour mode, the picture is dithered to eight colours. (It's difficult to use all 16 colours effectively for a colour dither without slowing things down.)

The greyscale uses an ordered (pattern-based) dither. The colour uses ordered dithering by default too, which is fast but pretty rough. If you'd prefer to sacrifice speed for better dithering, you can switch to error-diffused dithering by putting `dither-16col-fast' in a config file (see Config Files), or you can toggle the setting interactively:

`Alt-c'

If in 640x480x4 mode and using colour dithering, toggle between ordered and error-diffused dither.

All the features which work in 8-bit modes work in the 4-bit mode.

"Drawbacks of 15/16-bit Modes" Since 15 and 16-bit video modes do not have quite the same representation (and depth) that a file loaded as 24-bit does, there are some drawbacks to using them. Firstly, the image is converted to the 2-byte-per-pixel format as it is drawn (see Video Mode Issues, for the reason why zgv works this way); and secondly, the modes actually have less colour depth than 256-colour modes.

In explanation of that last point; although 15 and 16-bit video modes show many colours onscreen at once, there are fewer colours to choose from.

A good way to illustrate this point is by considering the number of greyscales each mode can display. In a 256-colour video mode, only 64 greys can be shown, since an 18-bit palette is used --- 2^(18/3) = 64. But with a 15-bit video mode, even fewer can be shown --- 2^(15/3) = 32. Because of the way that 16-bit video modes work, which is by providing the green channel with twice as much colour depth (i.e. an extra bit), they too can only show 32 greys. Put another way, 2^int(16/3) = 32. (Of course, 24/32-bit modes will show all 256 greyscales.)

"32-bit Video Modes" One oddity in mode-land is the 32-bit mode. Like 24-bit modes, 32-bit modes can display over 16 million colours. But there are no obvious advantages to using 32-bit modes, at least as far as zgv is concerned. So why does it support them?

Simply put, some SVGA hardware provides 32-bit modes without providing equivalent 24-bit ones. Hence zgv's support for them.

That should also explain why zgv treats them the way it does. Here's how it all works:

o When using zgv, you don't select a 32-bit mode directly. Instead, you select a 24-bit mode --- and if no matching 24-bit mode exists, but a matching 32-bit one does, zgv sneakily uses the 32-bit one behind your back. :-)

o zgv's `choose most similar mode' code prefers 24-bit modes to 32-bit ones, but similarly, if it has the 32-bit mode without the 24-bit one, it'll take the smoke-and-mirrors route.

o As an exception to the overall rule, when specifying modes on the command-line or in the config file, you do need to explicitly specify a 32-bit mode in order to get one.

For the most part you needn't worry about 32-bit modes, though; you can just ignore them and think in terms of 8/15/16/24-bit modes and you'll be ok.

"Disabling Video Modes" In some situations you might want to disable certain video modes. For example, perhaps your video card supports modes which your monitor cannot display; clearly you would want to disable these, as zgv only knows about your video card.

(To be fair though, if you have svgalib configured correctly for your monitor, this should never be a problem. See the libvga.config(5) man page for details.)

To disable video modes, you should give appropriate mode-bad entries in a config file (preferably /etc/zgv.conf for such system-wide configuration). See Config Variables, for details.

You could also do mode-all-bad then enable a few modes with mode-good entries --- but most cards support so many video modes that the mode-bad approach is usually the right one.

XZGV COMPATIBILITY

xzgv-keys on

in a config file (see

Config Files

). This enables an overriding routine which interprets xzgv-like keys to `native' zgv ones --- in practice, the effect is of some xzgv keys being added, overriding any conflicting zgv ones.

Space

View a picture file, or if the cursor is on a subdirectory, make that the current directory. (Like the native `Enter', which still works.)

`-'

Untag file.

`='

Tag file.

`Alt -'

(i.e. Alt-minus) Untag all files.

`Alt ='

(i.e. Alt-equals) Tag all files.

`Ctrl-n'

Rename file.

`Ctrl-d'

Delete file.

`q'

`Ctrl-q'

Exit zgv.

Note that there is no replacement for the usual zgv meaning of `Space'; that is, in xzgv-keys mode, there is (currently) no key which lets you toggle a file's tag state. (This will change if/when I add such a key to xzgv. :-))

In the viewer, there are these changes:

`b'

View previous file in dir.

`Space'

View next file in dir.

`Ctrl-Space'

Tag current file, then view next file in dir.

(In short, `b'/`Space'/`Ctrl-Space' act like the native `Backspace'/`Enter'/`Space'. The same mappings also apply when animating a multiple-image GIF file (see Multiple-image GIF Animation).)

`Ctrl-w'

Exit viewer (i.e. `close file').

`N'

Restore the picture orientation to normal. This undoes the effect of any mirrors, flips, and/or rotations. (Like the native `Alt-n'.)

There are some omissions in the viewer's xzgv-ish keys:

- The `Ctrl' + cursor-key alternatives to `h'/`j'/`k'/`l' don't exist, as these can't be distinguished from `normal' cursors given the way zgv reads keys.

- The alternative `Shift' + cursor-key means of paging up/down/left/right is similarly missing.

- Supporting `Ctrl-q' would have got in the way of slideshow pausing, so I decided against it, and omitted `q' from the viewer for some sort of consistency.

- Supporting `Tab' would break selecting some video modes, and probably would have seemed a bit surreal in zgv anyway. :-)

That about wraps it up for the keys... but, of course, there are other interface differences.

One is the way zgv has `flat' mouse menus for the selector/viewer, while xzgv has hierarchical ones. That would be nice to replicate, but I don't think I'm likely to.

A more dramatic difference (IMHO) is the way moving around the picture with the mouse works. In zgv, you move the screen around `over' the picture, with a fixed amount of mouse movement needed to cover any picture size. In xzgv, you move the picture around `under' the window, with the mouse movement needed being proportional to the picture size (this follows from the picture directly mimicking the mouse pointer's movement). The most obvious problem here is that moving the mouse right on zgv is like pressing cursor-right, while doing the same in xzgv is like pressing cursor-left. Now, I may eventually add an option to reverse zgv's reaction to mouse movement, but `fixing' the non-proportionality without a pointer onscreen might seem awfully strange.

Hmm. An interesting problem to tackle at some point, I suppose. :-)

FILE FORMATS

FILE TYPE IDENTIFICATION

.jpg

.jpeg

, zgv assumes it is a JPEG. This way of working is not @cc . always right, but it's much faster than the alternative (reading part of every single file) and is usually sufficient. (If it's not, you can enable slower `magic number'-based identification with `

Alt-m

' (see

File Selector Toggles

).)

FF D8

'. So if you start zgv with

zgv foo

, and foo is in a format supported by zgv (such as JPEG), the format will be figured out and the file loaded even though the `extension' is absent.

SUPPORTED FILE FORMATS

GIF. Multiple-image GIFs are treated specially (see

Multiple-image GIF Animation

JPEG.

PNG.

PBM/PGM/PPM, collectively known as `PNM'. This is a nice simple format used by pbmplus and netpbm.

BMP.

TGA (Targa).

PCX.

mrf. Mrf files can be converted to/from PBM with mrftopbm/pbmtomrf, and the format is documented in the mrf(5)

man page.

PRF. PRF is an extension of mrf, similarly converted with prftopnm/pnmtoprf, and documented in the prf(5)

man page.

XBM (X bitmap files).

XPM. zgv reads the file

/usr/X11R6/lib/X11/rgb.txt

to look up X colour names. (The location of the file is a compile-time option; you can edit

config.mk