"

 COPYRIGHT (c) 1991 by Claus Gittinger

	      All Rights Reserved

 This software is furnished under a license and may be used

 only in accordance with the terms of that license and with the

 inclusion of the above copyright notice.   This software may not

 be provided or otherwise made available to, or used by, any

 other person.  No title to or ownership of the software is

 hereby transferred.

"

Object subclass:#Image

	instanceVariableNames:'bytes width height bitsPerPixel depth colorMap maxPixelValue

		rowByteSize bitsPerSample samplesPerPixel photometric device

		deviceForm monoDeviceForm fullColorDeviceForm mask

		maskedPixelsAre0'

	classVariableNames:'Lobby DitherAlgorithm NumberOfDitherColors

		CollectGarbageWhenRunningOutOfColors FileFormats

		ImageNotFoundQuerySignal BadImageFormatQuerySignal

		ImageSaveErrorSignal FileCreationErrorSignal

		CannotRepresentImageSignal InformationLostQuerySignal'

	poolDictionaries:''

	category:'Graphics-Images'

!

!Image class methodsFor:'documentation'!

copyright

"

 COPYRIGHT (c) 1991 by Claus Gittinger

	      All Rights Reserved

 This software is furnished under a license and may be used

 only in accordance with the terms of that license and with the

 inclusion of the above copyright notice.   This software may not

 be provided or otherwise made available to, or used by, any

 other person.  No title to or ownership of the software is

 hereby transferred.

"

!

documentation

"

    this class provides (some time in the future) representation

    for all kinds of images (monochrome, greyscale and color)

    and will finally replace Form. 

    For now (only ;-) depths of 1, 2, 4, 8, 16 and 24 are supported.

    An Image keeps all of its information in a device independent way, 

    but may be associated to a device. 

    The data held keeps all information which was originally present, 

    even if the display-device has lower resolution.

    Therefore, it is possible to process and manipulate images without loosing 

    color information.

    Images may be created manually (by providing a pixel array),

    by screen capture or by reading a file (using an ImageReader).

    This gives a device independent image.

    For display, a device representation is required, which can be

    aquired by sending the 

        'onDevice:aDevice' 

    message to the image. This will create a (possibly dithered) device-form, 

    representing the image using the currently available colors.

    In rare cases, an explicit monochrome representation of the image is needed 

    (X servers take monochrome icons only), this can be created by sending

    it the message 

        'monochromeOn:aDevice'.

    Also, it is planned to generate another hi-color resolution version,

    which uses its own colormap and allows the use of all 256 colors on an 8bit display 

    (this is not currently implemented).

    An images pixel interpretation is controlled by the photometric instance variable

    and (if that is #palette) a colorMap.

    This is in contrast to the ST-80 way, where all of this info is in the colorMap

    (and using specialized colorMaps for b&w / greyScale images).

    This may change in future versions for more application compatibility.

    To convert pictures from/to external file-formats, image readers are used

    which have the file-format knowledge built in. 

    There are readers for most common formats available 

    (see ImageReader and especially subclasses such as TIFFReader, GIFReader etc.).

    File formats are handled by subclasses of ImageReader, which understand

    a specific format. You can add more readers, by adding an association

    such as ('.jpg' -> JPEGReader) to the class variable 'FileFormats' 

    (see the classes #initialize method, which sets up some default, and the

    patches/display.rc files, which add more).

    Some algorithms used here (especially dithering & color allocation) are

    experimental and far from being perfect (some are very slow). 

    For now, the most common cases have been optimized and perform reasonably

    fast - however, with uncommon depth/visualType combinations, you may

    run into slower fallback methods ...

    Much more work is needed if you plan to do heavy image processing and will

    (may) be done in the future if there is a demand for it ...

    Dithering can be controlled by the DitherAlgorithm classVariable:

       DitherAlgorithm:

       nil                  a simple threshold algorithm

                            (i.e. for mono, p<0.5 -> black, p>=0.5 -> white)

       #pattern             patterned dither

                            (for p, take dithered color to fill pixel;

                             uses dithering in color-class)

       #error               error diffusion dither (Floyd-Steinberg)

                            planned - not yet implemented.

    [instance variables:]

        width               <Integer>       the width in pixels

        height              <Integer>       the height in pixels

        bytes               <ByteArray>     the full image information

        photometric         <Symbol>        #rgb, #palette, #blackIs0 or #whiteIs0

        samplesPerPixel     <Integer>       the number of planes

        bitsPerSample       <Array>         the number of bits per plane

        colorMap            <Array>         only if photometric is #palette;

                                            maps pixel values to r/g/b values.

        device              <Workstation>   the device on which deviceForm,

                                            monoDeviceForm and lowResDeviceForm are

        deviceForm          <Form>          the device form which gives the best

                                            possible aproximation of the image on

                                            device using standard colors.

        monoDeviceForm      <Form>          the device form which gives a monochrome

                                            aproximation of the image on device.

        fullColorDeviceForm <Form>          the device form which gives the best

                                            possible aproximation of the image on

                                            device using private colors.

                                            (not yet implemented)

        mask                <ImageMask>     an optional mask;

                                            if non-nil, only pixels for which the

                                            corresponding mask bit is non-zero

                                            are drawn.

        maskedPixelsAre0    <Boolean>       a hint for image processors and drawers

                                            if true, masked pixels are known to be

                                            zero in the pixel bytes.

        bitsPerPixel                        not used in ST/X

        depth                               - these have been added in instVar-slots

        maxPixelValue                       - according to the ST-80's image class.

        rowByteSize                         - to allow loading of st-80 images

                                            - (which are stored as instVarAt:put: expressions)

    [class variables:]

        Lobby               <Registry>      keeps track of known images

                                            (for resource freeing with garbage collector)

        DitherAlgorithm     <Symbol>        defines how to dither

        NumberOfDitherColors <Integer>      defines, how many dither colors to use

        FileFormats         <Dictionary>    associates filename extensions to

                                            image reader classes (now set-up in startup-file)

        CollectGarbageWhenRunningOutOfColors

                            <Boolean>       if true, and we run out of available

                                            device colors during creation of a

                                            device image, collect garbage for

                                            possible image reclamation.

                                            If false, proceed immediately.

                                            Default is true.

        ImageNotFoundQuerySignal

                            <QuerySignal>   raised, if an image could not be loaded

                                            from a file. The parameter is the images

                                            fileName. 

                                            A handler may return a replacement

                                            image or proceed with nil.

                                            If unhandled, a nil is returned from the

                                            image creation.

        BadImageFormatQuerySignal

                            <QuerySignal>   raised, if an image could not be loaded

                                            from a file due to a file error or

                                            unsupported format. 

                                            A handler may return a replacement

                                            image or proceed with nil.

                                            If unhandled, a nil is returned from the

                                            image creation.

        ImageSaveErrorSignal

                            <Signal>        parent of errors below.

        FileCreationErrorSignal

                            <Signal>        file could not be created when saving an

                                            image.

        CannotRepresentImageSignal

                            <Signal>        the specified ImageReader cannot represent

                                            the given image.

        InformationLostQuerySignal

                            <Signal>        the specified ImageReader can represent

                                            the given image, but some information

                                            (typically color resolution) is lost.

                                            If unhandled, the save proceeds as usual.

    todo:

        support alpha masks

        cleanup the dithering & conversion code

    [See also:]

        Form Icon ImageReader

    [author:]

        Claus Gittinger

"

!

examples

"

    reading from a file (many formats are supported):

    inline image:

      default: depth=1 & #blackIs0

      with #whiteIs0 photometric

      with a colorMap

      a depth4 greyScale image:

      the following has the same effect:

      with reverse grey-interpretation:

      with 1-bit-per-pixel rgb interpretation:

      with 1/2/1 rgb interpretation:

      a 2/2/0 rgb image (i.e. no blue):

      a 0/0/4 rgb image (i.e. no red or green):

      a 2plane greyscale image:

      with colors:

      depth8 image with 3/3/2 rgb interpretation:

      depth8 image with 2/2/2 rgb interpretation:

    storing (only a few formats are currently supported):

    magnifying (any factor):