Class: JPEGReader

• Inheritance
• Description
• Related information
• Class protocol
  • defaults
  • initialization
  • testing
• Instance protocol
  • accessing
  • private
  • reading
  • writing
• Examples

Inheritance:

   Object
   |
   +--ImageReader
      |
      +--JPEGReader

Package:

stx:libview2

Category:

Graphics-Images-Readers

Version:

rev: 1.75 date: 2018/06/03 07:28:17

user: cg

file: JPEGReader.st directory: libview2

module: stx stc-classLibrary: libview2

Description:

Reader for JPEG images.

This uses the libpeg library to read the image

Only writing of depth24 images is currently supported.

Related information:

    Image
    Form
    Icon
    BlitImageReader
    FaceReader
    GIFReader
    MacOSXIconReader
    PBMReader
    PCXReader
    PNGReader
    ST80FormReader
    SunRasterReader
    TargaReader
    TIFFReader
    WindowsIconReader
    XBMReader
    XPMReader
    XWDReader

Class protocol:

 defaultCompressQuality

 defaultCompressQuality: percent

 initialize

install myself in the Image classes fileFormat table
for the `.jpg' and '.jpeg' extensions.

 canRepresent: anImage

return true, if anImage can be represented in my file format.
For now, only d24 images are supported.

 isValidImageFile: aFilenameOrString

return true, if aFileName contains a JPG image.
Only look at the file's name here ...

usage example(s):

self isValidImageFile:'xxx.jpg'

Instance protocol:

 app1SegmentHandler: aBlock

set a handler block for app1 segment data (geolocation in exif format)

 compressQuality: compressQualityOrNilForDefault

 forceDitherMode: something

set the dither mode, to one of #none or #ordered

 forceGrayscale: something

set the forceGrayscale mode; if true, grayScale images are
returned, even if the input contains a color image.

 app1SegmentCallback

return a callback function which invokes the app1SegmentHandlerBlock if defined.
This will be called to handle the exif segment, containing geolocation tags.
Return nil if there is no handler block defined

 create_jpeg_compress_struct

 create_jpeg_decompress_struct

 decompressChunkInto: aByteArray startingAt: index

 extractApp1DataFrom: data

= 'Exif' + 0-byte

 extractExifDataFrom: data

 fetchApp1SegmentData

msb first

 finish_compress

 finish_decompress

 get_error_message

 jpeg_getc

 start_decompress

 fromStream: aStream

read a JPG image from a stream.
For now, we can only read from a stdio-FILE with libjpeg
(need to write a mem-reader to read from a Smalltalk stream).
Therefore, any internal stream data is copied to a temporary file first,
and libjpg asked to decompress from there.
This should be fixed, if jpeg reading is a bottleneck in your app.

 compressScanlines

 save: anImage onFile: fileName

ex return.

 save: image onStream: aStream

save image in JPG-file-format onto aStream

Examples:

 |i i24 i2|

 Transcript printf:'gif original %d\n' with:( '../../goodies/bitmaps/gifImages/garfield.gif' asFilename fileSize ).
 i := Image fromFile:'../../goodies/bitmaps/gifImages/garfield.gif'.
 i24 := Depth24Image fromImage:i.
 JPEGReader save:i24 onFile:'test100.jpg'.
 i2 := Image fromFile:'test100.jpg'.
 Transcript printf:'jpg 100%% %d\n' with:( 'test100.jpg' asFilename fileSize ).
 i2 inspect

 |i i24 i2|

 Transcript printf:'gif original %d\n' with:( '../../goodies/bitmaps/gifImages/garfield.gif' asFilename fileSize ).
 i := Image fromFile:'../../goodies/bitmaps/gifImages/garfield.gif'.
 i24 := Depth24Image fromImage:i.
 JPEGReader save:i24 onFile:'test80.jpg'.
 i2 := Image fromFile:'test80.jpg'.
 Transcript printf:'jpg 80%% %d\n' with:( 'test80.jpg' asFilename fileSize ).
 i2 inspect

 |i i24 i2|

 i := Image fromFile:'../../goodies/bitmaps/gifImages/garfield.gif'.
 i24 := Depth24Image fromImage:i.
 JPEGReader new save:i24 onStream:('test50.jpg' asFilename writeStream) compressQuality:50.
 i2 := Image fromFile:'test50.jpg'.
 Transcript printf:'jpg 50%% %d\n' with:( 'test50.jpg' asFilename fileSize ).
 i2 inspect

 |i i24 i2|

 i := Image fromFile:'../../goodies/bitmaps/gifImages/garfield.gif'.
 i24 := Depth24Image fromImage:i.
 JPEGReader new save:i24 onStream:('test20.jpg' asFilename writeStream) compressQuality:20.
 i2 := Image fromFile:'test20.jpg'.
 Transcript printf:'jpg 20%% %d\n' with:( 'test20.jpg' asFilename fileSize ).
 i2 inspect

 |i i24 i2|

 i := Image fromFile:'../../goodies/bitmaps/gifImages/garfield.gif'.
 i24 := Depth24Image fromImage:i.
 JPEGReader new save:i24 onStream:('test10.jpg' asFilename writeStream) compressQuality:10.
 i2 := Image fromFile:'test10.jpg'.
 Transcript printf:'jpg 10%% %d\n' with:( 'test10.jpg' asFilename fileSize ).
 i2 inspect