ImageVice(TM) 1.0 Documentation

BoxTop Software, Inc.
101 N. Lafeyette Street
Starkville, MS 39759
(v) 1-601-324-1800
(f) 1-601-324-7352
http://www.boxtopsoft.com
ftp://ftp.boxtopsoft.com/pub
info@boxtopsoft.com


1: An Introduction to ImageVice(TM) technology
2: Basic usage of the ImageVice(TM) plug-in
3: Understanding the ImageVice(TM) controls
4: Trying out the ImageVice(TM) plug-in


An Introduction to ImageVice(TM) technology:

ImageVice(TM) is a new, proprietary color reduction technology, which makes possible
greatly improved compression ratios for all indexed file formats employing
lossless compression.

GIF, PNG, PICT and BMP are the most common graphics formats that can benefit from
ImageVice(TM) color reduction technology.

Applications for Web and multimedia graphics are tremendous. With ImageVice(TM)
color reduction smaller graphics files can be produced and smaller files
translate directly to faster loading web pages or more content possible for Web
and multimedia within the available storage constraints.

Lossless compression techniques such as Lempel-Ziv Welch "LZW", which the GIF
format uses, and Run-length Encoding "RLE", which is used by both the PICT and
BMP formats, is not variable and can not be made significantly more efficient.

Given the same data to compress, two LZW compressors will make the exact same
size compressed file.

The only variable in the final file size for indexed color graphics in GIF, PNG,
PICT or BMP formats is the initial color reduction step. It is that step that
determines the actual image data to compress.

The normal approach taken by color reduction algorithms is to create the most
mathematically accurate data to represent an image with a limited palette of
colors. This approach is perfectly fine when there are no considerations needed
for final file sizes, but in applications such as Web and multimedia graphics
file size is critical. It effects both speed and content capacity. The most
mathematically accurate data is the least compressible data in the case of color
reduction.

Human visual perception is not a mathematical process, though. The perceptual
criteria of the human visual system is very different to the algorithmic
processes of normal color reduction techniques.

ImageVice(TM) technology takes advantage of the perceptual processes of human vision
to model image data in such a way that it is not only visually accurate but also
much more compressible than otherwise.

The processes used in ImageVice(TM) technology can be controlled to a great extent
providing broad capability to produce images which are more visually accurate or
more compressible as needed, another advantage of ImageVice(TM)technology not
provided by other methods.

At the high end, image quality is much better than all other known color
reduction methods. Under normal usage settings ImageVice(TM) technology will exceed
other color reduction methods in both quality and compressibility of image data
produced.

Using extremely aggressive settings for compression will result in the smallest
possible files, but will begin to degrade image quality in noticeable but not
usually objectionable ways. Images produced with aggressive settings for
compressibility will have a painterly look to them.

There are indeed many comparisons between the process employed by ImageVice(TM) and
the process a painter would use to represent a scene as a realistically
recognizable image.

Basic usage of the ImageVice(TM) plug-in:

The ImageVice(TM) plug-in is a filter plug-in that acts on RGB mode images, and is
not tied to any particular graphics file format. This provides greater
flexibility for use.

To use the ImageVice(TM) plug-in, you first run the filter on your RGB image. This
changes the image to contain 256 or fewer colors. Then you change the document
mode in Photoshop to "indexed" color with the defaults that will appear in the
mode change dialog.

After you have changed to indexed mode, the image can be saved in the normal
manner that you would save GIF, PNG, PICT or BMP files.

For GIF graphics, you should use ImageVice(TM) in combination with a specialized
production tool like PhotoGIF(TM)*, which provides the best format specific
capability for making GIF files including more color reduction flexibility when
you need to use an existing palette such as the Web safe palette for a particular
image. (* PhotoGIF is currently in beta release for Windows at the time of this
writting.)

ImageVice(TM) can only create adaptive palettes based on the original colors in the
image.

Understanding the ImageVice(TM) controls:

The ImageVice(TM) plug-in has a single, relatively simple, dialog for specifying
color reduction parameters. Though, there are only six individual parameters,
which can be specified for color reduction, not all of these are immediately
obvious in their function.

The only controls in ImageVice(TM) that are comparable to controls found in other
color reduction tools are the depth menu and colors text box. Both of these
provide a means to set the number of colors to be used in the final image.

All other controls are unique to the ImageVice(TM) plug-in, and require a level of
understanding to get the maximum benefits possible from the ImageVice(TM) plug-in.

Balloon help is available in the ImageVice(TM) dialog to help understand the
function of the various controls and overcome the small learning curve.

More detailed explanation for controls are provided below.

1: Depth menu

The depth menu shows the lowest possible bit depth for the image given the
current number of colors specified, and can also be used to set the number of
colors specified to the maximum number of colors possible for a given bit depth.

Lowering the bit depth will improve an image's compressibility and reduce the
final file size. Very few images need to have more than 128 colors, which is the
maximum for a 7 bit image, to adequately represent them and many image require
even fewer colors.

2: Colors text box

The colors text box provides another means to set the number of colors to be
used. Odd numbers of colors can be specified using the colors text box, whereas
only even bit depths can be specified using the depth menu.

Even if lowering the set number of colors will not allow a lower bit depth, it
will still improve compressibility. An image using 120 colors will normally be
smaller than an image using 128 colors, though both images are 7 bit.

You should set the colors to the minimum number that will produce satisfactory
visual results for the individual image. If you are unsure of what this number
is, starting at 128 colors or 7 bit, is a good idea. Then you can undo the filter
and try a higher or lower number if it looks like fewer colors will do or more
colors are needed.

3: Clipping sliders

The clipping sliders are a set of two slider controls that are linked together in
their function.

The first slider is lower or dark color clipping. The second slider is upper or
light color clipping.

The lower clipping slider controls the threshold level for sampling dark colors
from the image. The range of the lower clipping slider corresponds directly to
gray component values 0 - 50. If the lower clipping slider was set to 50, no
colors would be sampled from the image that had a gray value lower or darker than
50 during color reduction.

The upper clipping slider controls the threshold level for sampling light colors
from the image. The range of the upper clipping slider is scaled to correspond to
gray component values 236 - 256 inversely, which is best thought of as the number
of high or light gray levels not to sample. Setting the upper clipping slider to
20, has the effect of no light colors with a gray values of 236 or above being
sampled during color reduction.

Mid range values for clipping will improve image compressibility by mapping all
colors that fall below the thresholding values to a single color in the ranges
subtleties in color are most difficult to distinguish and reducing entropy. Image
quality will also be improved with mid range clipping settings because more
palette entries will be available for mid range colors that are more easily
distinguishable.

You should reduce the lower or dark clipping setting for images that are
predominantly very dark colors to prevent harsh borders where thresholding occurs
and leave more palette entries available when they are actually needed in the
image.

Correspondingly, you should also reduce the upper clipping setting in images that
are predominantly very light colors for the same factors.

In images that have few dark or light areas, you can safely increase the settings
for clipping to very high values to improve compression.

4: Smoothing slider

The smoothing slider controls the tolerance for when very similar adjacent pixel
color values are merged.

This is a complex space variant process with only one controllable parameter, so
the action taken will vary significantly depending on the actual image, unlike
the upper and lower clipping sliders which have predictable results on all
images.

Increasing the value for smoothing will increase the compressibility of the image
and normally has little apparent visual impact on the final image. However, if
the original image has predominant areas that are very smooth linear color
blends, high smoothing settings will become more obvious and possibly
undesirable.

5: Convergence sliders

The two sliders for convergence work together to specify a ratio for an internal
mechanism that there is no sane way to explain.

The first slider is an overall tolerance value for this mechanism and the second
slider provides a measure of relational amplitude.

Though, the process of convergence is not easily explained in words, the visual
effects are apparent and their nature is easily understood from visual example.

To better understand the visual effects of convergence settings, you should
compare images filtered with both convergence sliders set to zero to an image
filtered with default convergence values and then one filtered with both
convergence sliders at maximum.

Convergence settings are primarily responsible for both incredible compression
levels that can be achieved with the ImageVice(TM) plug-in and at the highest
settings the aforementioned "painterly" look to images.

The default settings for convergence work very well with almost all images, and
produce very good quality to compressibility ratios.

Increasing the first convergence slider value will have less visually apparent
effect than the second, which should rarely be used at its maximum setting.
However, when maximum compressibility is the priority, convergence settings
should be increased first as they have the most impact on compressibility.

When maximum quality is desired the convergence sliders can be set to values
lower than the defaults, but it is not recommended for compressibility's sake to
turn convergence off completely. Very low settings will still significantly
improve compressibility without any noticeable visual effect on the image.

6: Image preview

The image preview is only thumbnail size, which is less than perfect for the
purpose of color reduction, but the most that can practically be provided given
the computational complexity involved. Of all the great things that can be said
about the ImageVice(TM) plug-in, "fast" is not one of them.

The image preview does provide some amount of quick feedback on chosen settings,
but it should be realized that the thumbnail isn't as high in quality as the
final image will be because of the scale factor.

7: OK and Cancel

Both do the usual thing.

Trying out the ImageVice(TM) plug-in:

The ImageVice(TM) plug-in demo is fully functional, but will only work with the six
provided test images, which it calculates a checksum to identify. These six
images were chosen very carefully to be the most representative test suite for
all types of images from photographs to rendered graphics. They are "combination"
images, artificially made with elements from all types of images.

You will be able to experiment with the ImageVice(TM) plug-in on the images
provided, and compare the results to other tools. Take care not to save over the
original test images. Any modification to them and the ImageVice(TM) plug-in will no
longer work on them.


If you have any questions while evaluating the ImageVice(TM) plug-in demo that this
documentation does not answer, please let us know.

Contact information is below.

BoxTop Software, Inc.
101 N. Lafeyette Street
Starkville, MS 39759
(v) 1-601-324-1800
(f) 1-601-324-7352
http://www.boxtopsoft.com
ftp://ftp.boxtopsoft.com/pub
info@boxtopsoft.com

Sales contact:
Cindy Johnson - cindy@boxtopsoft.com

Support Contact:
Susan Brewer - susan@boxtopsoft.com

Company Contact:
Travis Anton - travis@boxtopsoft.com

Development Contact:
Richard Anton - ranton@boxtopsoft.com


ImageVice(TM) 1.0 is Copyright 1997 BoxTop Software, Inc. All Rights Reserved.
ImageVice(TM) and  PhotoGIF(TM) are Trademarks of BoxTop Software, Inc. All other
trademarks are recognized as the properties of their respective holders.

Document published: 11/10/97

Copyright 1997 BoxTop Software, Inc. All Rights Reserved. 
