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https://issues.apache.org/jira/browse/SANSELAN-75?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Gary Lucas updated SANSELAN-75:
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Attachment: IndexColorPalette.tif
Tracker_Item_75_23_Apr_2012.patch
The attached patch addresses the issue. Since there are no TIFF format files
of the relevant type in the Sanselan test suite, I am also attaching one.
> Improve speed of TIFF Index-Color Palette
> ------------------------------------------
>
> Key: SANSELAN-75
> URL: https://issues.apache.org/jira/browse/SANSELAN-75
> Project: Commons Sanselan
> Issue Type: Improvement
> Components: Format: TIFF
> Reporter: Gary Lucas
> Attachments: IndexColorPalette.tif, Tracker_Item_75_23_Apr_2012.patch
>
> Original Estimate: 0h
> Remaining Estimate: 0h
>
> TIFF supports an 8-bit-per-pixel, "indexed color" model in which the values
> in the source data give indices into a fixed palette of color settings.
> Unpacking data in this format requires two steps: (1) reading and unpacking
> the palette in the source file, (2) performing a look-up operation for each
> pixel to map the index value to a color. A similar approach was used in the
> original GIF specification and, checking wikipedia, it appears that it is
> also supported by PNG and BMP. TIFF files in this format are used
> extensively in mapping and Geographic Information System implementation.
> The current inplementation of the PhotometicInterpreterPalette for TIFF files
> has an inefficiency in that it performs the unpacking operation from step one
> each time a new pixel is read. Thus, if a file contains three million red
> pixels, the byte-manipulation for the color red is repeated three million
> times. It would be more efficient for the PhotometricInterpreterPalette
> class to perform the unpacking operation once, in its constructor. Since
> there are a maximum of 256 colors in an 8-bit palette, this approach would
> require moderate use of memory.
> In time tests this approach reduced the reading time for a large TIFF file by
> about 13 percent (for details on the timing procedures, see Tracker Item 58):
> Unmodified Code: 1204.9 ms.
> After change: 1049.7 ms.
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