| Both sides previous revision
Previous revision
Next revision
|
Previous revision
Last revision
Both sides next revision
|
images [2016/03/02 15:16]
christian [Implementation] |
images [2016/09/24 08:15]
dokuadmin ↷ Page moved from pdf:images to images |
| </code> | </code> |
| |
| In PDF images are defined by the number of bits per color component (1, 2, 4, 8 or 16 bit). The colorspace defines the number of components and their layout for a pixel. Any colorspace permitted in PDF can be used (see [[Colors]]). For images converted from Smalltalk, only ''/DeviceRGB'' (3 components), ''/DeviceGray'' (1 component) and ''/Indexed'' (1 component) are relevant. The ''/Indexed'' colorspace in PDF can only hold up to 255 colors. | In PDF images are defined by the number of bits per color component (1, 2, 4, 8 or 16 bit). The colorspace defines the number of components and their layout for a pixel. Any colorspace permitted in PDF can be used (see [[:colors]]). For images converted from Smalltalk, only ''/DeviceRGB'' (3 components), ''/DeviceGray'' (1 component) and ''/Indexed'' (1 component) are relevant. The ''/Indexed'' colorspace in PDF can only hold up to 255 colors. |
| |
| A ''PDF.ImageXObject'' is a stream whose contents is a byte string with the pixel bits. A row ends at the byte boundary. A row with one pixel with 3 components of 1 bits (= 3 bits), uses 1 byte (8 bit) for the row. As any stream, ImageXObjects can be compressed using filters. By default, ''/FlateDecode'' (zip) is used. | A ''PDF.ImageXObject'' is a stream whose contents is a byte string with the pixel bits. A row ends at the byte boundary. A row with one pixel with 3 components of 1 bits (= 3 bits), uses 1 byte (8 bit) for the row. As any stream, ImageXObjects can be compressed using filters. By default, ''/FlateDecode'' (zip) is used. |
| The conversion methods are implemented in the ''Graphics.Image'' hierarchy. To convert a Smalltalk image to PDF with ''asPDF'', the method ''writePixelsTo: anImageXObject'' transfers the actual pixels from the Smalltalk to the PDF image. The other direction uses the method ''readPixelsFrom: anImageXObject'' which transfers the PDF pixels to the Smalltalk image. | The conversion methods are implemented in the ''Graphics.Image'' hierarchy. To convert a Smalltalk image to PDF with ''asPDF'', the method ''writePixelsTo: anImageXObject'' transfers the actual pixels from the Smalltalk to the PDF image. The other direction uses the method ''readPixelsFrom: anImageXObject'' which transfers the PDF pixels to the Smalltalk image. |
| |
| {{ :pdf:bitfiddling306x408.png?200&nolink|Work sketch for bit fiddling}} | {{ :pdf:bitfiddling200x266.png?nolink|Work sketch for bit fiddling}} |
| |
| The default behavior is to transfer the pixels one by one. For each pixel, the bits are read from the specified location in the source image bytes and interpreted as color (''valueAtPoint:''). This color is then converted to the target bits which are written to the specified location in the target image bytes (''valueAtPoint:put:''). While these two pixel accessors are correct and well tested for any kind of image, they are very slow. | The default behavior is to transfer the pixels one by one. For each pixel, the bits are read from the specified location in the source image bytes and interpreted as color (''valueAtPoint:''). This color is then converted to the target bits which are written to the specified location in the target image bytes (''valueAtPoint:put:''). While these two pixel accessors are correct and well tested for any kind of image, they are very slow. |