<div dir="ltr"><div><div><div><div>Hi Ivan,<br><br></div>Unfortunately the color table API does not support the functionality that was added to the RAT API in RFC40. As a result, dealing with large color tables can be problematic.<br>
<br></div>Yes the HFA driver does report colors correctly as 0-255 with the color table API and one solution could be to add RFC40 functionality to the color table API. However, it does seem that it does make sense to be able to manipulate colors from the RAT API for e.g. setting colors based on the value(s) found in other attribute columns easily. <br>
<br></div>I accept that no consistency can be expected for user defined columns (usage == GFU_Generic) but I would have though applications could depend on the color columns since they are marked as such by their usage. In fact the documentation for the usage values (<a href="http://www.gdal.org/gdal_8h.html#a27bf786b965d5227da1acc2a4cab69a1">http://www.gdal.org/gdal_8h.html#a27bf786b965d5227da1acc2a4cab69a1</a>) does specify them to be 0-255 so this seems to have been the intention and is maybe just a bug in the HFA driver. <br>
<br></div>Sam.<br></div><div class="gmail_extra"><br><br><div class="gmail_quote">On 13 January 2014 15:18, Ivan Lucena <span dir="ltr"><<a href="mailto:lucena_ivan@hotmail.com" target="_blank">lucena_ivan@hotmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div><div dir="ltr">Hi Sam,<br><br>In GDAL color table is supported by the GDALColorTable <a href="http://gdal.org/classGDALColorTable.html" target="_blank">http://gdal.org/classGDALColorTable.html</a> not by GDALRasterAttributeTable <a href="http://gdal.org/classGDALRasterAttributeTable.html" target="_blank">http://gdal.org/classGDALRasterAttributeTable.html</a>. <br>
<br>The GDALColorTable is a little bit limited but it is pretty much consistent across all the drivers that support it. For example, when you say that HFA reports RGBA with values from 0..1 as RAT it probably reports the correct 0..255 as GDALGetColorTable or it doesn't report it at all, because of the GDALColorTable limitation, like data type or number of colors.<br>
<br>But IMHO, there is no reason to expect consistency on the representation of color table from a driver RAT. An RAT could be user defined or generated by some driver or application. <br><br>What you are seem is that some drivers are using, or maybe abusing, the freedom format of RAT to report information than can be understood by some particular application or software (mea culpa on one of those).<br>
<br>Best regards,<br><br>Ivan<br><br><div><hr>Date: Mon, 13 Jan 2014 13:06:01 +1300<br>From: <a href="mailto:gillingham.sam@gmail.com" target="_blank">gillingham.sam@gmail.com</a><br>To: <a href="mailto:gdal-dev@lists.osgeo.org" target="_blank">gdal-dev@lists.osgeo.org</a><br>
Subject: [gdal-dev] Color Columns in Raster Attribute Tables<div><div class="h5"><br><br><div dir="ltr"><div>Hi List,<br><br>There appears to be an
inconsistency in the way color columns are handled within Raster
Attribute Tables (RATs) by different drivers. Color columns are currently identified by their 'usage' setting - GFU_Red, GFU_Green, GFU_Blue and GFU_Alpha. The HFA driver presents
color columns as doubles between 0 and 1 as this is how they are stored
in the file. The IDRISI driver presents them as integers between 0 and
255 like the Color Table API. Code that uses color columns from the RAT
API currently needs to know which driver it is using, defeating one of the aims of GDAL. <br>
<br>I propose that the RAT API be defined so that color columns
always appear as Integer 0-255 no matter what type and range they are stored as.
This would make the RAT API consistent with the Color Table API and would mean a change to the HFA driver<br><br>Another
option is that flags are added to the RAT SetValue, GetValueAs* and
ValuesIO calls to specify the conversion to/from the native type. This
seems a bigger change.<br>
<br>Any thoughts?<br><br></div>Sam.<br></div>
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</blockquote></div><br></div>