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images [2016/02/22 17:09] christian [Implementation] |
images [2016/02/22 17:19] christian [To be done] |
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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 | + | 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. |
| - | + | ||
| - | These are not implemented (yet), so 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. Just the basic **FlateDecode** filter is used by default to compress | + | |
| + | 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. | ||
| + | Secondly, PDF can have images in other colorspaces than RGB or Grayscale; most notable is ''/ | ||