=for rcs $Id: Image.pod,v 1.4 2002/05/14 13:22:32 dk Exp $

=head1 NAME

Image - Bitmap routines

=head1 DESCRIPTION

I<Prima::Image>, I<Prima::Icon> and I<Prima::DeviceBitmap> are classes
for bitmap handling, including file and graphic input and
output. I<Prima::Image> and I<Prima::DeviceBitmap> are descendants of
I<Prima::Drawable> and represent bitmaps, stored in memory.
I<Prima::Icon> is a descendant of I<Prima::Image>
and contains a transparency mask along with the regular data.

=head1 USAGE

Images usually are represented as a memory area, where pixel data
are stored row-wise. The Prima toolkit is no exception, however,
it does not assume that the GUI system uses the same memory format.
The implicit conversion routines are called when I<Prima::Image> is
about to be drawn onto the screen, for example. The conversions
are not always efficient, therefore the I<Prima::DeviceBitmap> class
is intoduced to represent a bitmap, stored in the system memory
in the system pixel format. These two basic classes serve the different
needs, but can be easily converted to each other, with C<image> and
C<bitmap> methods. I<Prima::Image> is a more general bitmap representation,
capable of file and graphic input and output, plus it is supplied with
number of conversion and scaling functions. The I<Prima::DeviceBitmap>
class has almost none of additional functionality, and is targetet
to efficient graphic input and output.

=head2 Graphic input and output

As descendants of I<Prima::Drawable>, all I<Prima::Image>, I<Prima::Icon> and 
I<Prima::DeviceBitmap> objects are subject to three-state painting mode - 
normal ( disabled ), painting ( enabled ) and informational.
I<Prima::DeviceBitmap> is, however, exists only in the enabled state,
and can not be switched to the other two.

When an object enters the enabled state, it serves as a canvas, and
all I<Prima::Drawable> operations can be performed on it. When the object
is back to the disabled state, the graphic information is stored into
the object associated memory, in the pixel format, supported by the toolkit.
This information can be visualised by using one of C<Prima::Drawable::put_image>
group methods. If the object enters the enabled state again, the graphic
information is presented as an initial state of a bitmap.

It must be noted, that if an implicit conversion takes place after an
object enters and before it leaves the enabled state, as it is with
I<Prima::Image> and I<Prima::Icon>, the bitmap is converted to the system pixel
format. During such conversion some information can be lost, due to downsampling,
and there is no way to preserve the information. This does not happen with
I<Prima::DeviceBitmap>.

Image objects can be drawn upon images, as well as on the screen and L<Prima::Widget>
objects. This operation is performed via one of I<Prima::Drawable::put_image> group methods
( see L<Prima::Drawable>),
and can be called with the image object disregarding the paint state. The following
code illustrates the dualism of an image object, where it can serve both as a drawing surface 
and as a drawing tool:

    my $a = Prima::Image-> create( width => 100, height => 100, type => im::RGB);
    $a-> begin_paint;
    $a-> clear;
    $a-> color( cl::Green);
    $a-> fill_ellipse( 50, 50, 30, 30);
    $a-> end_paint;
    $a-> rop( rop::XorPut);
    $a-> put_image( 10, 10, $a);
    $::application-> begin_paint;
    $::application-> put_image( 0, 0, $a);
    $::application-> end_paint;

It must be noted, that C<put_image>, C<stretch_image> and C<put_image_indirect>
are only painting methods that allow drawing on an image that is in its 
paint-disabled state. Moreover, in such context they only allow C<Prima::Image>
descendants to be passed as a source image object. This functionality does not
imply that the image is internally switched to the paint-enabled state and
back; the painting is performed without switching and without interference with
the system's graphical layer.


=head2 File input and output

Depending on the toolkit configuration, images can be read and written in
different formats. This functionality in accessible via C<load()>
and C<save()> methods. L<Prima::image-load> is dedicated to the 
description of loading and saving parameters, that can be passed to the methods,
so they can handle different aspects of file format-specific options,
such as multi-frame opertaions, auto conversion when a format does not
support a particular pixel format etc. In this document, C<load()>
and C<save()> methods are illustrated only in their basic, single-frame
functionality. When called with no extra parameters, these methods fail
only if a disk I/O error occured or an unknown image format was used. 

When an image is loaded, the old bitmap memory content is discarded,
and the image attributes are changed accordingly to the loaded image.
Along with these, an image palette is loaded, if available, and
a pixel format is assigned, closest or identical to the pixel format 
in the image file.

=head2 Pixel formats

I<Prima::Image> supports a number of pixel formats, governed by the C<::type>
property. It is reflected by an integer value, a combination of C<im::XXX>
constants. The whole set of pixel formats is represented by colored formats,
like, 16-color, 256-color and 16M-color, and by grayscale formats, mapped to
C data types - unsigned char, unsigned short, unsigned long, float and double.
The grayscale formats are subdivided to real-number formats and complex-number
format; the last ones are represented by two real values per pixel, containing
the real and the imaginary values.

I<Prima::Image> can also be initialized from other formats, that it does not
support, but can convert data from. Currently these are
represented by a set of permutations of 32-bit RGBA format, and 24-bit BGR format. 
These formats can only be used in conjunction with C<::data> property.

The conversions can be performed between any of the supported formats ( to do
so, C<::type> property is to be set-called ). An image of any of these formats 
can be drawn on the screen,
but if the system can not accept the pixel format ( as it is with non-integer or
complex formats ), the bitmap data are implicitly converted. The conversion
does not change the data if the image is to be output; the conversion is performed 
only when the image is to be served as a drawing surface. If, by any reason, it is
desired that the pixel format is not to be changed, the C<::preserveType> property
must be set to 1. It does not prevent the conversion, but it detects if the image
was implicity converted inside C<end_paint()> call, and reverts it to
its previous pixel format.

There are situations, when a pixel format conversion must be made with
downsampling. One of three downsampling methods can be selected -
normal, 8x8 halftoning and error diffusion. These can be set to
the C<::conversion> property with one of C<ict::XXX> constants.
When there is no information loss, C<::conversion> property is not used.

Another special case of conversion is a conversion with a palette.

  $image-> type( im::bpp4);
  $image-> palette( $palette);

and 

  $image-> palette( $palette);
  $image-> type( im::bpp4);

produce different results, but none of these takes into account eventual 
palette remapping, because C<::palette> property does not change bitmap pixel
data, but overwrites palette information. A proper call syntax is

  $image-> set(
     palette => $palette,
     type    => im::bpp4,
  );

This call produce correct results, if palette pixel mapping is desired.
NB: C<im::bpp4> type in the examples above is a 16-color pixel format,
but it can be any indexed format. 

=head2 Data access 

The pixel values can be accessed in I<Prima::Drawable> style, via C<::pixel>
property. However, I<Prima::Image> introduces several helper functions,
for different aims. The C<::data> property is used to set or retrieve 
a scalar representation of bitmap data. The data are expected to be lined 
up to a 'line size' margin ( 4-byte boundary ), which is calculated as

  $lineSize = int(( $image->width * ( $image-> type & im::BPP) + 31) / 32) * 4; 

This is a default line size, but C<::data> can be accompanied with a
write-only flag 'lineSize':

  $image-> set( width => 1, height=> 2);
  $image-> type( im::RGB);
  $image-> set(
     data => 'RGB----RGB----',
     lineSize => 7,
  );
  print $image-> data, "\n";

  output: RGB-RGB-

Although it is possible to perform all kinds of calculations and modification
with the pixels, returned by C<::data>, it is not advisable unless the speed
does not matter. Standalone PDL package, and lately Prima-derived IPA package
provide routines for data and image analysis. I<Prima::Image> itself provides
only the simpliest statistic information, namely: lowest and highest pixel values, 
pixel sum, sum of square pixels, mean, variance, and standard deviation.

=head2 Prima::Icon

I<Prima::Icon> inherits all properties of I<Prima::Image>, 
and it also provides a 1-bit depth transparency mask.
This mask can also be loaded and saved into image files,
if the format supports a transparency information.

Alike I<Prima::Image> C<::data> property, I<Prima::Icon> C<::mask>
property provides access to the binary mask data.
The mask can be updated automatically, after an icon object
was subject to painting or other change. The auxiliary 
properties C<::autoMasking> and C<::maskColor> regulate  
mask update procedure. For example, if an icon was loaded with
the color ( vs. bitmap ) transparency information, the binary
mask will be generated anyway, but it will be also recorded that
a particular color serves as a transparent indicator, so eventual
conversions can rely on the color value, instead of the mask bitmap.

If an icon is drawn upon a graphic canvas, the image output
is constrained to the mask. On raster displays it is typically
simulated by a combination of and- and xor- operation modes,
therefore attempts to put an icon with C<::rop>, different from
C<rop::CopyPut>, usually fail.

=head1 API

=head2 Prima::Image properties

=over

=item conversion TYPE

Selects type of dithering algorithm, when downsampling 
takes place. TYPE is one of C<ict::XXX> constants:

   ict::None            - no dithering
   ict::Halftone        - 8x8 halftone dithering
   ict::ErrorDiffusion  - ordered dithering

As an example, if a 4x4 color image with every pixel set to RGB(64,64,64),
converted to a 1-bit image, the following results occur:

   ict::None:
     [ 0 0 0 0 ]
     [ 0 0 0 0 ]
     [ 0 0 0 0 ]
     [ 0 0 0 0 ]

   ict::Halftone:
     [ 0 0 0 0 ]
     [ 0 1 0 1 ]
     [ 0 0 0 0 ]
     [ 0 1 0 1 ]

   ict::ErrorDiffusion:
     [ 0 0 0 1 ]
     [ 0 0 0 1 ]
     [ 0 0 0 1 ]
     [ 0 0 1 0 ]

=item data SCALAR

Provides access to the bitmap data. On get-call, returns
all bitmap pixels, aligned to 4-byte boundary. On set-call,
stores the provided data with same alignment. The alignment
can be altered by submitting 'lineSize' write-only flag
to set call. ( see L<Data access> ).

=item height INTEGER

Manages the vertical dimension of the image data.
On set-call, the image data are changed accordingly to the new height,
and depending on C<::vScaling> property,
the pixel values are either scaled or truncated.

=item hScaling BOOLEAN

If 1, the bitmap data will be scaled when image changes its
horizonal extent. If 0, the data will be stripped or padded 
with zeros.

=item mean

Returns mean value of pixels.
Mean value is C<::sum> of pixel values, divided by number of pixels.

=item palette [ @PALETTE ] 

A color palette, used for representing 1, 4, and 8-bit bitmaps,
when an image object is to be visualized.

=item pixel ( X_OFFSET, Y_OFFSET ) PIXEL

Provides per-pixel access to the image data when 
image object is in disabled paint state. Otherwise,
same as C<Prima::Drawable::pixel>.

=item preserveType BOOLEAN

If 1, reverts the image type to its old value if an
implicit conversion was called during C<end_paint()>.

=item rangeHi

Returns maximum pixel value in the image data.

=item rangeLo

Returns minimum pixel value in the image data.

=item size WIDTH, HEIGHT 

Manages dimensions of the image. On set-call,
the image data are changed accordingly to the new dimensions,
and depending on C<::vScaling> and C<::hScaling> properties,
the pixel values are either scaled or truncated.

=item stats ( INDEX ) VALUE

Returns one of calculated values, that correspond to INDEX, which is one 
of the following C<is::XXX> constants:

   is::RangeLo  - minimum pixel value
   is::RangeHi  - maximun pixel value
   is::Mean     - mean value
   is::Variance - variance
   is::StdDev   - standard deviation
   is::Sum      - sum of pixel values
   is::Sum2     - sum of squares of pixel values

The values are re-calculated on request and cached.
On set-call VALUE is stored in the cache, and is returned on next get-call.
The cached values are discarded every time the image data changes.

These values are also accessible via set of alias
properties: C<::rangeLo>, C<::rangeHi>, C<::mean>, C<::variance>,
C<::stdDev>, C<::sum>, C<::sum2>.

=item stdDev

Returns standard deviation of the image data. 
Standard deviation is the square root of C<::variance>. 

=item sum

Returns sum of pixel values of the image data

=item sum2

Returns sum of squares of pixel values of the image data

=item type TYPE

Governs the image pixel format type. TYPE is a combination
of C<im::XXX> constants. The constants are collected in groups:

Bit-depth constants provide size of pixe is bits. Their actual 
value is same as number of bits, so C<im::bpp1> value is 1,
C<im::bpp4> - 4, etc. The valid constants represent bit depths 
from 1 to 128:

   im::bpp1
   im::bpp4
   im::bpp8
   im::bpp16
   im::bpp24
   im::bpp32
   im::bpp64
   im::bpp128

The following values designate the pixel format category:

   im::Color
   im::GrayScale
   im::RealNumber
   im::ComplexNumber
   im::TrigComplexNumber

Value of C<im::Color> is 0, whereas other category constants 
represented by unique bit value, so combination of
C<im::RealNumber> and C<im::ComplexNumber> is possible.

There also several mnemonic constants defined: 

   im::Mono          - im::bpp1
   im::BW            - im::bpp1 | im::GrayScale
   im::16            - im::bpp4
   im::Nibble        - im::bpp4
   im::256           - im::bpp8
   im::RGB           - im::bpp24
   im::Triple        - im::bpp24
   im::Byte          - gray 8-bit unsigned integer
   im::Short         - gray 16-bit unsigned integer 
   im::Long          - gray 32-bit unsigned integer 
   im::Float         - float
   im::Double        - double
   im::Complex       - dual float
   im::DComplex      - dual double
   im::TrigComplex   - dual float
   im::TrigDComplex  - dual double

Bit depths of float- and double- derived pixel formats 
depend on a platform.

The groups can be masked out with the mask values:

   im::BPP      - bit depth constants
   im::Category - category constants
   im::FMT      - extra format constants 

The extra formats are the pixel formats, not supported by C<::type>,
but recognized within the combined set-call, like

   $image-> set(
      type => im::fmtBGRI,
      data => 'BGR-BGR-',
   );

The data, supplied with the extra image format specification will
be converted to the closest supported format. Currently, the following
extra pixel formats are recognized:

   im::fmtBGR
   im::fmtRGBI
   im::fmtIRGB
   im::fmtBGRI
   im::fmtIBGR

=item variance

Returns variance of pixel values of the image data.
Variance is C<::sum2>, divided by number of pixels 
minus square of C<::sum> of pixel values.

=item vScaling BOOLEAN

If 1, the bitmap data will be scaled when image changes its
vertical extent. If 0, the data will be stripped or padded 
with zeros.

=item width INTEGER

Manages the horizontal dimension of the image data.
On set-call, the image data are changed accordingly to the new width,
and depending on C<::hScaling> property,
the pixel values are either scaled or truncated.

=back

=head2 Prima::Icon properties

=over

=item autoMasking TYPE

Selects whether the mask information should be updated
automatically with C<::data> change or not. Every
C<::data> change is mirrored in C<::mask>, using TYPE,
one of C<am::XXX> constants:

   am::None           - no mask update performed
   am::MaskColor      - mask update based on ::maskColor property
   am::Auto           - mask update based on corner pixel values

The C<::maskColor> color value is used as a transparent color if
TYPE is C<am::MaskColor>. The transparency mask generation algorithm,
turned on by C<am::Auto> checks corner pixel values, assuming that
majority of the corner pixels represents a transparent color. Once
such color is found, the mask is generated as in C<am::MaskColor>
case.

When image C<::data> is stretched, C<::mask> is stretched accordingly,
disregarding the C<::autoMasking> value.

=item mask SCALAR

Provides access to the transparency bitmap. On get-call, returns
all bitmap pixels, aligned to 4-byte boundary in 1-bit format. On set-call,
stores the provided transparency data with same alignment.

=item maskColor COLOR

When C<::autoMasking> set to C<am::MaskColor>, COLOR 
is used as a transparency value.

=back 

=head2 Prima::DeviceBitmap properties

=over

=item monochrome BOOLEAN

A read-only property, that can only be set during creation,
reflects whether the system bitmap is black-and-white 1-bit (monochrome) or not.
The color depth of a bitmap can be read via C<get_bpp()> method; monochrome
bitmaps always have bit depth of 1.

=back 

=head2 Prima::Image methods 

=over

=item bitmap

Returns newly created I<Prima::DeviceBitmap> instance, 
with the image dimensions and with the bitmap pixel 
values copied to.

=item codecs

Returns array of hashes, each describing the supported image
format. If the array is empty, the toolkit was set up so
it can not load and save images. 

See L<Prima::image-load> for details.

This method can be called without object instance.

=item dup

Returns a duplicate of the object, a newly created I<Prima::Image>, with all
information copied to it.

=item extract X_OFFSET, Y_OFFSET, WIDTH, HEIGHT

Returns a newly created image object with WIDTH and HEIGHT dimensions,
initialized with pixel data from X_OFFSET and Y_OFFSET
in the bitmap.

=item get_bpp

Returns the bit depth of the pixel format. Same as C<::type & im::BPP>.

=item get_handle

Returns a system handle for an image object.

=item load FILENAME [ %PARAMETERS ]

Loads image file FILENAME into an object, and returns the success flag.
The semantics of C<load()> is extensive, and can be influenced by 
PARAMETERS hash. C<load()> can be called either in a context of an existing object,
then a boolean success flag is returned, or in a class context, then a newly
created object ( or C<undef> ) is returned. If an error occurs, C<$@> variable
contains the error description string. These two invocation semantics are 
equivalent:

   my $x = Prima::Image-> create();
   die "$@" unless $x-> load( ... );

and

   my $x = Prima::Image-> load( ... );
   die "$@" unless $x;

See L<Prima::image-load> for details.

=item map COLOR

Performs iterative mapping of bitmap pixels, setting every pixel
to C<::color> property with respect to C<::rop> type if a pixel
equals to COLOR, and to C<::backColor> property with respect 
to C<::rop2> type otherwise. 

C<rop::NoOper> type can be used for color masking.

Examples:

   width => 4, height => 1, data => [ 1, 2, 3, 4]
   color => 10, backColor => 20, rop => rop::CopyPut

   rop2 => rop::CopyPut
   input: map(2) output: [ 20, 10, 20, 20 ]

   rop2 => rop::NoOper
   input: map(2) output: [ 1, 10, 3, 4 ]

=item resample SRC_LOW, SRC_HIGH, DEST_LOW, DEST_HIGH

Performs linear scaling of gray pixel values from range (SRC_LOW - SRC_HIGH)
to range (DEST_LOW - DEST_HIGH). Can be used to visualize
gray non-8 bit pixel values, by the code:

   $image-> resample( $image-> rangeLo, $image-> rangeHi, 0, 255);

=item save FILENAME, [ %PARAMETERS ]

Stores image data into image file FILENAME, and returns the success flag.
The semantics of C<save()> is extensive, and can be influenced by 
PARAMETERS hash. If error occurs, C<$@> variable
contains error description string.

See L<Prima::image-load> for details.

=back

=head2 Prima::Icon methods 

=over

=item split

Returns two new I<Prima::Image> objects of same dimension.
Pixels in the first is are duplicated from C<::data> storage,
in the second - from C<::mask> storage.

=item combine DATA, MASK

Copies information from DATA and MASK images into C<::data>
and C<::mask> property. DATA and MASK are expected to be images
of same dimension.

=back

=head2 Prima::DeviceBitmap methods 

=over

=item icon

Returns a newly created I<Prima::Icon> object instance, with the 
pixel information copied from the object.

=item image

Returns a newly created I<Prima::Image> object instance, with the 
pixel information copied from the object.

=item get_handle

Returns a system handle for a system bitmap object.

=back

=head1 AUTHOR

Dmitry Karasik, E<lt>dmitry@karasik.eu.orgE<gt>.

=head1 SEE ALSO

L<Prima>, L<Prima::Drawable>, L<Prima::image-load>, L<Prima::codecs>.
