Changes between Version 68 and Version 69 of WKTRaster/SpecificationWorking03

Timestamp:

Apr 23, 2011, 8:38:43 AM (13 years ago)

Author:

Bborie Park

Comment:

ST_AsJPEG

WKTRaster/SpecificationWorking03

@@ -219 +219 @@
  ST_AsJPEG(raster, integer, "GRAYSCALE", integer, min, max, text) - allow specifying the band number to convert and the quality
 
+Bborie: The JPEG format has several limitations:
+
+  1. JPEG only allows 1 (greyscale) or 3 (RGB) bands of data
+
+  2. JPEG only supports 8BUI pixeltype
+
+  3. JPEG cannot embed spatial reference information within the file but can have an associated world file
+
+To address the limitations:
+
+  1. Use ST_Band to specify which band(s) should be passed to the ST_AsJPEG function. Variations of ST_AsJPEG are made available that allows specifying a band index. If a raster whose number of specified bands does not equal 1 or 3 is provided, a warning is raised and the first or the first three bands are used.
+
+  2. Throw an exception if any of the specified bands is not 8BUI. The user should use ST_Reclass to convert any non-8BUI bands to 8BUI.
+
+  3. Nothing can be done.
+
+A proposed set of variations of the ST_AsJPEG function:
+
+1. ST_AsJPEG(rast raster, options text[])
+
+    rast: the raster with one or three bands in 8BUI pixel type to generate a JPEG image from
+
+    options: array of creation options to pass to the GDAL JPEG driver
+
+{{{
+ST_AsJPEG(rast, ARRAY['QUALITY=90', 'PROGRESSIVE=ON'])
+}}}
+
+2. ST_AsJPEG(rast raster)
+
+    Like !#1 above but use the driver's default creation options
+
+3. ST_AsJPEG(rast raster, nbands int[], options text[])
+
+    nbands: an integer array specifying the band indices of the raster to include in the JPEG file
+
+{{{
+ST_AsJPEG(rast, ARRAY[1,3,6], ARRAY['QUALITY=50'])
+}}}
+
+4. ST_AsJPEG(rast raster, nbands int[])
+
+    Like !#3, but use the default creation options
+
+{{{
+ST_AsJPEG(rast, ARRAY[1,3,6])
+}}}
+
+5. ST_AsJPEG(rast raster, nbands int[], quality int)
+
+    quality: number between 10 and 100 indicating image quality
+
+{{{
+ST_AsJPEG(rast, ARRAY[1,2,3], 90)
+}}}
+
+6. ST_AsJPEG(rast raster, nband int, options text[])
+
+    nband: index of the band to include
+
+{{{
+ST_AsJPEG(rast, 2, ARRAY['QUALITY=25'])
+}}}
+
+7. ST_AsJPEG(rast raster, nband int, quality int)
+
+{{{
+ST_AsJPEG(rast, 5, 75)
+}}}
+
+8. ST_AsJPEG(rast raster, nband int)
+
+{{{
+ST_AsJPEG(rast, 4)
+}}}
 
 ----
@@ -380 +455 @@
     rast: the raster with one or three bands in 8BUI or 16BUI pixel type to generate a PNG image from
 
-    options: array of creation options to pass to the GDAL JPEG driver
+    options: array of creation options to pass to the GDAL PNG driver
 
 {{{