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<TITLE>paintlib - C++ - Features</TITLE>
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<P><B>Bitmap Operations</B>
<P> paintlib works on bitmaps. The abstract class PLBmp defines an interface
for bitmap storage and manipulation. The actual details of storage are
defined in derived classes. The contents of a bitmap can be changed either
via Filter objects or by directly accessing the bits. Among others, filters
for resizing, cropping, rotating and blurring an image are included. PLBmp
implements color depth conversion from and to 1, 8, 24 and 32 bpp. The standard
equality and assignment operators are implemented as well and convert
between the derived classes transparently. paintlib provides basic classes
for pixels, points and rectangles.
<P>Currently, six classes derived from PLBmp are defined: PLWinBmp for
windows DIBs (Device Independent Bitmaps), PLAnyBmp for simple OS-independent
storage, PLDIBSection for windows DIB sections, the experimental PLDDrawBmp
class that stores images in DirectDraw system memory surfaces, PLDirectFBBmp
for DirectFB surface support and PLSDLBmp, which stores bitmaps as libsdl
(Simple Directmedia Layer) surfaces. New
classes can be defined for other operating systems and storage formats,
the only restriction being that pixels in one line are stored consecutively
and not as separate planes. To be compatible with the decoders, a bitmap
class must define formats with 1, 8 and 32 bpp. Bitmaps with alpha channels
are supported.
<P> [Bernard Delmes piclook (one of the sample programs) contains PLDrawDibBmp,
a derived bitmap class that uses the windows DrawDIB api for blitting.]
<P> There is virtually no difference in speed between using the OS-independent
interface and directly accessing OS-dependent data. The power of this
design is demonstrated by the testdib demo. This demo includes classes
which implement complex bitblts with alpha information, resizing, and
transparency in an OS-independent fashion. The classes are documented
in the read.me file in the testdib directory.
<P><b>Filters</b>
<P>Filters encapsulate operations on bitmaps. To the user of the library,
a filter is similar to a function that can be called for a bitmap. However,
filters are independent of the actual bitmap class: Each filter works
with every bitmap class. In addition, putting filters in separate classes
allows you to use filters as part of a command pattern: you can put filters
in a queue and parameterize algorithms with different filters, among others.
Here is a list of some of the filters currently included with paintlib:
<ul>
<li>Contrast</li>
<li>Crop</li>
<li>Extract alpha channel</li>
<li>Convert to grayscale</li>
<li>Intensity</li>
<li>Lightness</li>
<li>Color quantization (conversion of true-color images to 256 colors)</li>
<li>Bilinear resize</li>
<li>Gaussian blur</li>
<li>Threshold</li>
</ul>
<p><B>Image File Decoding</B> </p>
<P> paintlib can decode image files and store the data in an object of any
of the PLBmp-derived classes. Supported file formats are GIF, PGM, PPM,
PNG, TGA, TIFF, JPEG, PCX, Photoshop PSD, Windows BMP, Amiga IFF, SGI and Mac PICT as
well as TIFF previews in EPS files. Support for PNG is through the PNG
reference library libpng. TIFF is supported through use of Sam Leffler's
libtiff. This library is the most complete implementation of the TIFF
standard that I know of. The Independent JPEG Group's libjpeg provides
solid support for the JPEG/JFIF format. The GIF decoder uses libungif
(maintained by Eric Raymond). The Photoshop decoder allows access to the
individual layers saved in the file as separate bitmaps.
<P>Be aware that using a gif decoder in your program can might cause legal
problems - see the libungif documentation for details. If you'd like to
use paintlib without gif support, you can compile it without this support.
In fact, you can exclude support for any file types you don't need.
<P> The library is capable of auto-detection of the image file type. This
is done by actually examining the file contents, not by checking the extension.
Input data can come from memory or disk - or from a custom data source.
Under windows, images linked into the .exe as resources can also be loaded.
All data is converted to 32 bpp or 8 bpp before being handed to the application.
1 bpp tiffs are an exception to this rule - they get handed to the application
as 1 bpp.
<P>Files to be decoded can be on the local file system, somewhere in memory or
any place that's reachable via an URL.
<P>paintlib allows you to get image information (size, bit depth,...) before
the actual decoding process starts.
<P><B>Image File Encoding</B>
<P> The encoding classes store images. Currently implemented are BMP, TIFF
(via libtiff), JPEG (via libjpeg) and PNG (via libpng). Data storage is
handled by data sink classes. A data sink for disk files is provided;
others can be implemented.
<P><B>EXIF Support</B>
<P>paintlib provides support for EXIF tags embedded in JPEG files. These
tags are inserted by digital cameras and provide additional metadata: when the picture
was taken, what aperture was used, etc.
<P><B>Open Design</B>
<P> One of the primary design goals for paintlib was openness for expansion.
Implementing additional en- and decoders is simple because many basic
operations (data source management, MSB/LSB conversion, error handling,...)
have been taken care of already. Integrating libpng, for example, took
Gilles and me about two days (total) of work. The data sources and sinks
and the bitmap format can be tailored to suit the needs of the users.
The filter interface is very thin, so creating new filters is easy.
<p><br>
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