pdf:images
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pdf:images [2016/02/22 17:09] – [Implementation] christian | pdf:images [2016/03/02 15:15] – [Implementation] christian | ||
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Bitmapped images are described in chapter 8.9 //Images// on page 203 of the {{pdf32000_2008.pdf# | Bitmapped images are described in chapter 8.9 //Images// on page 203 of the {{pdf32000_2008.pdf# | ||
+ | |||
+ | The implementation is in package '' | ||
===== Usage ===== | ===== Usage ===== | ||
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renderer paintXObject: | renderer paintXObject: | ||
</ | </ | ||
+ | |||
+ | {{demo20_ImagesUsage.pdf}} shows the result with an example image. | ||
+ | |||
+ | {{demo21_Images.pdf}} shows some PDF features of images (masking, rotation, interpolation, | ||
===== Object Models ===== | ===== Object Models ===== | ||
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The conversion methods are implemented in the '' | The conversion methods are implemented in the '' | ||
+ | |||
+ | {{ : | ||
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 ('' | 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 ('' | ||
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When converting such image optimized by converting the palette and using the same indexes for the pixels allowing direct reuse of the image bytes, the /Indexed colorspace may contain several entries for the same color. Converting such an ImageXObject back to Smalltalk will not recreate the least significant 5 bits leading to slightly different colors as in the original. But for 8 bit RGB usage, it will not make any difference. Although this does not feel proper, it will not make much difference in practice. But the speed up of the optimization is worth it. | When converting such image optimized by converting the palette and using the same indexes for the pixels allowing direct reuse of the image bytes, the /Indexed colorspace may contain several entries for the same color. Converting such an ImageXObject back to Smalltalk will not recreate the least significant 5 bits leading to slightly different colors as in the original. But for 8 bit RGB usage, it will not make any difference. Although this does not feel proper, it will not make much difference in practice. But the speed up of the optimization is worth it. | ||
- | ===== Disclaimer | + | ===== To be done ===== |
- | Not covered are the special | + | ==== Filter ==== |
+ | |||
+ | Although all Smalltalk images can be used for PDF, not all PDF images can be transformed to Smalltalk images. For one, several | ||
* **RunLengthDecode** 8 bit monochrome images | * **RunLengthDecode** 8 bit monochrome images | ||
* **CCITTFaxDecode** CCITT encoded 1 bit monochrome images | * **CCITTFaxDecode** CCITT encoded 1 bit monochrome images | ||
* **JBIG2Decode** JBIG2 encoded 1 bit monochrome images | * **JBIG2Decode** JBIG2 encoded 1 bit monochrome images | ||
* **DCTDecode** JPEG encoded 8 bit grayscale or color images | * **DCTDecode** JPEG encoded 8 bit grayscale or color images | ||
- | * **JPXDecode** JPEG2000 encoded grayscale or color images | + | * **JPXDecode** JPEG2000 encoded grayscale or color images. |
+ | |||
+ | This means that it is not possible to extract such images from PDF. Nor is it possible to store images in the most efficient way in a PDF. This feature is valuable and I hope to implement some of the filters in the not too distant future. | ||
- | These are not implemented (yet), so that it is not possible to extract | + | Secondly, PDF can have images in other colorspaces than RGB or Grayscale; most notable |
+ | ==== Inlined Images ==== | ||
+ | Images in PDF can be inlined in the /Contents stream instead of storing them in the /Resources as /XObject. Only a subset of legal PDF images can be inlined and it is discouraged for large images. Even though, I have not seen such image in a real-world PDF, this feature should be implemented for completeness. |
/var/www/virtual/code4hl/html/dokuwiki/data/pages/pdf/images.txt · Last modified: 2016/03/02 15:19 by christian