The Display Modes Menu
In addition to displaying an image in a window, XV can also display images on the root (background) window of your X display. The Display Modes popup menu lets you select where (and how) XV will display the image. Also, the Display Modes menu lets you specify how colors will be picked to display the image. To view the display modes popup menu, click and hold the Display modes button. The current display mode will be shown with a checkmark next to it. To select a new mode, drag the mouse down to the desired mode, and release the mouse button.
Figure 3 Display, 24/8 Bit, Algorithms
Image Display Modes:
Root: Tiled: The image is displayed in the root window. One image is displayed aligned with the top-left corner of the screen. The image is then duplicated towards the bottom and right edges of the screen, as many times as necessary to fill the screen.
Root: Integer Tiled: Similar to Root: Tiled, except that the image is first shrunk so that its width and height are integer divisors of the screen's width and height. This keeps the images along the bottom and right edges of the screen from being `chopped-off'.
Root: Mirrored: Tiles the original image with versions that have been horizontally flipped, vertically flipped, and both horizontally and vertically flipped. This gets rid of the sharp dividing lines where tiled images meet.
Root: Integer Mirrored: Like Root: Mirrored, but also does the integerization described under the Root: Integer Tiled entry.
Root: Center Tiled: Like Root: Tiled, but it positions the images so that one of them is centered on the screen, and the rest are tiled off in all directions.
Root: Centered: Displays a single image centered in the root window, surrounded by black, or your choice of any other solid color.
Root: Centered, Warp: Displays a single image centered in the root window, surrounded by a black and white `warp' pattern.
Root: Centered, Brick: Displays a single image centered in the root window, surrounded by a black and white `brick' pattern.
Root: Symmetrical Tiled: Tiles images on the root window such that the images are symmetric around the horizontal and vertical center lines of the screen.
Root: Symmetrical Mirrored: Like the Root: Symmetrical Tiled mode, but the images are also mirrored.
Note: If you quit XV while displaying an image on the root window, the image will remain in the root window, and the colors used by the image will remain allocated.
Read/Write Colors: When turned on, forces XV to use read/write color cells (ignored and disabled in Use Std. Colormap mode, below). Normally, XV allocates read-only color cells, which allows it to share colors with other programs. If you use read/write color cells, no other program can use the colormap entries that XV is using, and vice-versa. The major reason to do such a thing is that using read/write color cells allows the Apply function in the XV color editor window to operate much faster, and allows the Auto-Apply while dragging feature to be used at all.
Normal Colors: XV's normal color allocation mode. For any given picture, XV figures out what colors should be allocated, and tries to allocate them (read-only or read/write, as determined by the Read/Write Colors setting). If any color allocation fails, XV will try a few other tricks, and map the remaining colors (that it didn't get) into the closest colors that it did get.
Perfect Colors: When Perfect Colors is turned on, XV proceeds as in the Normal Colors case. If any color allocation request fails, all colors are freed, and XV creates itself a private colormap, and tries again.
Use Own Colormap: Like Perfect Colors, but it doesn't even try to allocate out of the system colormap. Instead, it starts off by creating its own colormap, and allocating from there.
Use Std. Colormap: Instead of picking the (generally unique) colors that each image requires, this mode forces all images to be displayed (dithered) using the same set of (standard) colors. With this option you can display many images simultaneously (by running more than one copy of XV) without instantly running out of colors. (This mode is the only one available when you are displaying images in 24-bit mode).
XV has two primary modes of operation. It can either operate (internally) on 8-bit images with a colormap, or it can operate on 24-bit TrueColor images. In 8-bit mode, any image loaded, be it a 1-bit black-and-white image, or a 24-bit RGB image, will be converted into an 8-bit colormapped image. It will be manipulated as such, and when it is saved, it will be converted back into the appropriate format. Note that when working with 24-bit images, the 24-bit data is thrown away.
In 24-bit mode, the 24-bit data is kept around and manipulated. You can measure pixel values, and if you have a 24-bit display, the image will be shown in 24-bits. If you don't have a 24-bit display, the image will be dithered with a standard set of colors. If you save the image, all 24-bits of the data will be written (assuming the format supports 24-bit images).
The 24/8 Bit Menu
This menu lets you see which mode XV is currently operating in, and lets you change modes. You can also force XV to remain in the current mode and select how the program will convert 24-bit images into 8-bit images.
24-bit mode: Forces the program into 24-bit mode when selected. If you are currently working on an 8-bit image, it will be converted into a 24-bit image and the 8-bit image will be thrown away.
Lock Current Mode: Normally, XV will switch between 8 and 24-bit modes based on the image type. Turning this option on will force XV to remain in the current mode.
Quick 24->8: Converts 24-bit images to 8-bit images by dithering with a fixed 6x6x6 RGB colormap. It is the quickest of the three algorithms, but also generally produces the worst images.
Slow 24->8: The default algorithm. Takes about twice as long as the Fast algorithm. Uses the median cut algorithm to pick a set of 256 colors, and then dithers with these colors.
Best 24->8: The slowest of the algorithms. Can take up to ten times as long as the Slow algorithm. Uses a cleverer version of the median-cut algorithm to pick a better set of 256 colors than the slow algorithm and does not dither.