p4pApp (1.1 - July 03) Documentation
User's Page
Synopsis: The application p4pApp has the usual
Microsoft Windows Document/View structure and look with a toolbar. Because
the input file is treated as read-only several of the menu items of Document/View
have been removed. When a file is opened it is displayed on the window
and the user may select one of several operations to apply on the file.
The result is displayed next to the original. There is a special toolbar
button for saving the resulting image. The application can read and write
only PNG files. Non trivial changes from version 1.0 are marked in blue.
Purpose: To evaluate the effects of the pack4png
algorithm both in the quality of an image and in the space savings. When
an image is first read or after the reset button (see Toolbar below) has
been pressed the processed image is displayed next to the original. Otherwise
the last two processed images are displayed size by side. In all case
the required space is also displayed.
The Menus: There are only two of them File
and Help. The former has entries for Open, Exit
and up to 8 most recently used files (MRUs). The latter has three entries:
About p4pApp, Documentation, and Locations. Selecting Documentation
causes the default browser to display this document. Selecting Locations displays
the directories used by the program.
The Toolbar: There are 16
toolbar buttons with icons as shown below.
Starting from the left they have the following functionality.
- Open file has the usual Microsoft Windows functionality. The selected
PNG image is displayed on the window with its top left corner near the
top left corner of the window. In addition, the image dimensions and
size as well as the value of D
are displayed. A colored circle (green, yellow,
or red) is also displayed next to the value of D providing a hint on
whether PNG (or GIF) is preferable to JPEG or not. The diameter of the
circle suggests whether packing will be helpful.
- Button labeled "SZ" (for Split Zones): This is a push button.
When set, zones of sparse intensities are split and their intensities
are assigned to the adjacent strong zones. This increases compression
at the expense of introducing aliasing.
- Buttons labeled "1" through "5" cause pack4png
to be invoked with the value of the compression argument equal
to the label of the button. The resulting image is displayed to the
right or (if it is very wide) below the input image. However the next
time one of these button is pressed the previously processed image is
displayed in the place of the input image. In this way the user can
compare the effects of two different parameter selections. (See also
the description of the "Rs" button below.) The display also
includes the size of the image and the root mean square error.
- Button labeled with a red "?": It causes a text dialogue
to pop up where the user can type any value to be used for the compression
argument in the call of pack4png(). The rest of the operation
is the same as for the numbered buttons.
- Button labeled "1" overlayed to "GcT"
transforms the image using compression 1 but with provisions
to optimize its encoding for a 6x6x6 global color table (used in some
GIF implementations as a "web-safe" palette). Since this applications
does not use palettes (or color tables) the file is saved in true color
PNG format and some other application must be used to convert it to
a paletted format..
- Button labeled "Q" creates a Quantized version of the input
image by displaying only the n most signigicant bits. The image
is displayed to the right or (if it is very wide) below the input image.
The initial value of n is 3. However, if pack4png()
has been called previously, the value of n is chosen to mtach
as close as possible the number of zones found.
- Button labeled "EQ" (for Equalized Quantization) creates
a Quantized version by using histogram equalization. The number of zones
equals the number found by the most recent call of pack4png().
If no such call has been made, 8 zones are used.
- Button labeled "Rs" (for Reset or Restore) causes the display
of the input image only so that it can be compared with the processed
image produced next.
- Button labeled "S" (for Save) saves in PNG format the last
processed image. Its functionality is similar to that of the "Save
As" button in Micorsoft Windows applications.
- Button labeled "W" (for Web): A Web page is created
and displayed immediately. The directory where such pages are
saved can be found from the Locations menu item. Such a web
page is probably the best place to view the effect of the parameters
selected. It displays the original plus 8 other versions.
- Button labeled "ALL": It allows the
user to go through all the images in a directory sequentially. If no
image has been read the directory is the default image directory (it
can be found from the Locations menu item.) If an image, say
x001.png, has been read by some other command, then the ALL command
examines the directory of that image starting with x001.png. Each imageis
displayed together with its transformation using compression
1. After the user clicks on the "YES" button of a dialogue
box the next image is displayed.
- Button labeled with a yellow "?" has the usual Microsoft
Windows functionality.
Remarks: In order to keep the program simple there are
no printing options.
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