Changes between Version 83 and Version 84 of WKTRaster/SpecificationWorking03

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Timestamp:
05/24/11 11:13:43 (2 years ago)
Author:
dustymugs
Comment:

expired old notes for ST_AsJPEG

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  • WKTRaster/SpecificationWorking03

    v83 v84  
    104104 
    105105'''ST_AsJPEG(raster, quality) -> JPEG as "bytea"'''[[BR]] 
    106 Return the raster as a JPEG encoded as a PostgreSQL bytea. By default quality is set to 75, but this option can be used to select other values. Values must be in the range 10-100. Low values result in higher compression ratios, but poorer image quality. Values above 95 are not meaningfully better quality but can but substantially larger. (copied from http://www.gdal.org/frmt_jpeg.html) 
    107  
    108  
    109 '''Open Question:''' Is JPEG export limited to raster having 8 bit unsigned integer pixeltype (8BUI)? 
    110  
    111 [http://www.gdal.org/frmt_jpeg.html See how GDAL do it]. It converts only 8 bits rasters. Should we do the same? 
    112  
    113 Otherwise, how do we convert other types to 8BUI? e.g. 16BUI or 8BSI? 
    114  
    115 Pierre: It might be more simple to ignore pixeltypes other than 8BUI but it would be very convenient to have a way to quickly export elevation data for example as a JPEG. It would be nice to have an elegant solution to this. Maybe something inspired from !MapServer. 
    116  
    117 Proposition one (Pierre): ST_AsJPEG could simply (optionally when the pixeltype is not 8BUI) map the ST_Maximum() and ST_Minimum() value to 0-255. ST_Maximum() and ST_Minimum() are not in the spec yet but this could be on nice usage of it. They will imply caching the min and max when importing and editing. Both function should ignore the !NoDataValues. They could also be two parameters passed to ST_AsJPEG(raster, quality, min, max). 
    118  
    119 Proposition two: There could also be just one parameter (string) defining a mapping method: 
    120  
    121  * Method "None": No mapping. This is possible only for 8BUI. 
    122  
    123  * Method "!MaxMinValue": Use the Max and the Min cached in the raster. e.g. for 16BSI (min, max) -> (-2033, 2456) -> (round((-2033 - -2033)/(2456 - -2033)*255), round((2456 - -2033)/(2456 - -2033)*255)) -> (0, 255).[[BR]] 
    124 [[BR]]This is equivalent to ST_AsJPEG(raster, quality, ST_Minimum(rast), ST_Maximum(rast)) 
    125  
    126  * Method "!MaxMinType": Use the Max and the Min allowed by the type. e.g. for 16BSI (min, max) -> (-2033, 2456) -> (round((-2033 - -32768)/(32767 - -32768)*255), round((2456 - -32768)/(32767 - -32768)*255)) -> (120, 137)[[BR]] 
    127 [[BR]]This would be equivalent to ST_AsJPEG(raster, quality, ST_BandPixelTypeMin(rast), ST_BandPixelTypeMax(rast)). Both functions (ST_BandPixelTypeMin & ST_BandPixelTypeMax) are not yet planned and I could not find an SQL query that returns the equivalent range for a type. [http://groups.google.nl/group/microsoft.public.sqlserver.programming/browse_thread/thread/46512c2691da4607/6743f4aea485c6d1 One possible solution.] 
    128  
    129  
    130 mloskot: ATM, I have no thoughts on this issue. 
    131  
    132 '''Open Question:''' Is JPEG export limited to raster having 1 or 3 bands? 
    133  
    134 [http://www.gdal.org/frmt_jpeg.html See how GDAL do it]. It converts only 1 or 3 band rasters. Should we do the same? In this case 1 band rasters would be exported as a greyscale JPEG having R G and B identical and 3 band rasters would be interpreted as R, G and B. 
    135  
    136 Pierre: I think the answer should be yes. I don't see how we could have a 2 band raster fit into RGB. 
    137  
    138 mloskot: I agree, the answer should be yes. 
    139  
    140 '''Here is an attempt to define the different versions of the function:''' 
    141  
    142 The most minimalistic versions of the function should assume band 1, 2 and 3 as being r, g, b and the quality equal to 75: 
    143  
    144  ST_AsJPEG(raster) -quality = 75 
    145  
    146 A variant allow specifying the quality: 
    147  
    148  ST_AsJPEG(raster, integer) 
    149  
    150 Another variant should enable us to specify which band correspond to the r, the g and the b: 
    151  
    152  ST_AsJPEG(raster, integer, integer, integer) - raster, rband, gband, bband, quality=75 
    153  
    154  ST_AsJPEG(raster, integer, integer, integer, integer) - raster, rband, gband, bband, quality 
    155  
    156 Another version should be designed to be used with a future ST_Band(raster) function. In this case there is no attempt to extract r, g or b band from any passed raster: 
    157  
    158  ST_AsJPEG(raster, raster, raster) 
    159  
    160  ST_AsJPEG(raster, raster, raster, integer) -with the quality param 
    161  
    162 Another series should allow converting 1 band raster with pixel of type 8BUI to a grayscale JPEG (Carefull study of the GDAL behavior when converting a single band to JPEG should be done before confirming these functions): 
    163  
    164  ST_AsJPEG(raster, "GRAYSCALE") - convert only band 1 with quality = 75 
    165  
    166  ST_AsJPEG(raster, "GRAYSCALE", integer) - convert only band 1 with specified quality 
    167  
    168  ST_AsJPEG(raster, integer, "GRAYSCALE") - allow specifying the band number to convert 
    169  
    170  ST_AsJPEG(raster, integer, "GRAYSCALE", integer) - allow specifying the band number to convert and the quality 
    171  
    172 Another series should allow converting 1 band raster of ANY pixel type to a grayscale JPEG. Pixel types different than 8BUI should be mapped according to specified min, max values and a mapping mode: "!MaxMinValue" (default) or "!MaxMinType". 
    173  
    174  ST_AsJPEG(raster, "GRAYSCALE", min, max, text) - convert only band 1 with quality = 75 
    175  
    176  ST_AsJPEG(raster, "GRAYSCALE", integer, min, max, text) - convert only band 1 with specified quality 
    177  
    178  ST_AsJPEG(raster, integer, "GRAYSCALE", min, max, text) - allow specifying the band number to convert 
    179  
    180  ST_AsJPEG(raster, integer, "GRAYSCALE", integer, min, max, text) - allow specifying the band number to convert and the quality 
    181  
    182 Bborie: The JPEG format has several limitations: 
     106 
     107The JPEG format has several limitations: 
    183108 
    184109  1. JPEG only allows 1 (greyscale) or 3 (RGB) bands of data 
    … …  
    255180ST_AsJPEG(rast, 4) 
    256181}}} 
     182 
     183''OLD NOTES'' 
     184 
     185~~Return the raster as a JPEG encoded as a PostgreSQL bytea. By default quality is set to 75, but this option can be used to select other values. Values must be in the range 10-100. Low values result in higher compression ratios, but poorer image quality. Values above 95 are not meaningfully better quality but can but substantially larger. (copied from http://www.gdal.org/frmt_jpeg.html)~~ 
     186 
     187 
     188~~'''Open Question:''' Is JPEG export limited to raster having 8 bit unsigned integer pixeltype (8BUI)?~~ 
     189 
     190~~[http://www.gdal.org/frmt_jpeg.html See how GDAL do it]. It converts only 8 bits rasters. Should we do the same?~~ 
     191 
     192~~Otherwise, how do we convert other types to 8BUI? e.g. 16BUI or 8BSI?~~ 
     193 
     194~~Pierre: It might be more simple to ignore pixeltypes other than 8BUI but it would be very convenient to have a way to quickly export elevation data for example as a JPEG. It would be nice to have an elegant solution to this. Maybe something inspired from !MapServer.~~ 
     195 
     196~~Proposition one (Pierre): ST_AsJPEG could simply (optionally when the pixeltype is not 8BUI) map the ST_Maximum() and ST_Minimum() value to 0-255. ST_Maximum() and ST_Minimum() are not in the spec yet but this could be on nice usage of it. They will imply caching the min and max when importing and editing. Both function should ignore the !NoDataValues. They could also be two parameters passed to ST_AsJPEG(raster, quality, min, max).~~ 
     197 
     198~~Proposition two: There could also be just one parameter (string) defining a mapping method:~~ 
     199 
     200~~ * Method "None": No mapping. This is possible only for 8BUI.~~ 
     201 
     202~~ * Method "!MaxMinValue": Use the Max and the Min cached in the raster. e.g. for 16BSI (min, max) -> (-2033, 2456) -> (round((-2033 - -2033)/(2456 - -2033)*255), round((2456 - -2033)/(2456 - -2033)*255)) -> (0, 255).[[BR]]~~ 
     203~~[[BR]]This is equivalent to ST_AsJPEG(raster, quality, ST_Minimum(rast), ST_Maximum(rast))~~ 
     204 
     205~~ * Method "!MaxMinType": Use the Max and the Min allowed by the type. e.g. for 16BSI (min, max) -> (-2033, 2456) -> (round((-2033 - -32768)/(32767 - -32768)*255), round((2456 - -32768)/(32767 - -32768)*255)) -> (120, 137)[[BR]]~~ 
     206~~[[BR]]This would be equivalent to ST_AsJPEG(raster, quality, ST_BandPixelTypeMin(rast), ST_BandPixelTypeMax(rast)). Both functions (ST_BandPixelTypeMin & ST_BandPixelTypeMax) are not yet planned and I could not find an SQL query that returns the equivalent range for a type. [http://groups.google.nl/group/microsoft.public.sqlserver.programming/browse_thread/thread/46512c2691da4607/6743f4aea485c6d1 One possible solution.]~~ 
     207 
     208 
     209~~mloskot: ATM, I have no thoughts on this issue.~~ 
     210 
     211~~'''Open Question:''' Is JPEG export limited to raster having 1 or 3 bands?~~ 
     212 
     213~~[http://www.gdal.org/frmt_jpeg.html See how GDAL do it]. It converts only 1 or 3 band rasters. Should we do the same? In this case 1 band rasters would be exported as a greyscale JPEG having R G and B identical and 3 band rasters would be interpreted as R, G and B.~~ 
     214 
     215~~Pierre: I think the answer should be yes. I don't see how we could have a 2 band raster fit into RGB.~~ 
     216 
     217~~mloskot: I agree, the answer should be yes.~~ 
     218 
     219~~'''Here is an attempt to define the different versions of the function:'''~~ 
     220 
     221~~The most minimalistic versions of the function should assume band 1, 2 and 3 as being r, g, b and the quality equal to 75:~~ 
     222 
     223~~ ST_AsJPEG(raster) -quality = 75~~ 
     224 
     225~~A variant allow specifying the quality:~~ 
     226 
     227~~ ST_AsJPEG(raster, integer)~~ 
     228 
     229~~Another variant should enable us to specify which band correspond to the r, the g and the b:~~ 
     230 
     231~~ ST_AsJPEG(raster, integer, integer, integer) - raster, rband, gband, bband, quality=75~~ 
     232 
     233~~ ST_AsJPEG(raster, integer, integer, integer, integer) - raster, rband, gband, bband, quality~~ 
     234 
     235~~Another version should be designed to be used with a future ST_Band(raster) function. In this case there is no attempt to extract r, g or b band from any passed raster:~~ 
     236 
     237~~ ST_AsJPEG(raster, raster, raster)~~ 
     238 
     239~~ ST_AsJPEG(raster, raster, raster, integer) -with the quality param~~ 
     240 
     241~~Another series should allow converting 1 band raster with pixel of type 8BUI to a grayscale JPEG (Carefull study of the GDAL behavior when converting a single band to JPEG should be done before confirming these functions):~~ 
     242 
     243~~ ST_AsJPEG(raster, "GRAYSCALE") - convert only band 1 with quality = 75~~ 
     244 
     245~~ ST_AsJPEG(raster, "GRAYSCALE", integer) - convert only band 1 with specified quality~~ 
     246 
     247~~ ST_AsJPEG(raster, integer, "GRAYSCALE") - allow specifying the band number to convert~~ 
     248 
     249~~ ST_AsJPEG(raster, integer, "GRAYSCALE", integer) - allow specifying the band number to convert and the quality~~ 
     250 
     251~~Another series should allow converting 1 band raster of ANY pixel type to a grayscale JPEG. Pixel types different than 8BUI should be mapped according to specified min, max values and a mapping mode: "!MaxMinValue" (default) or "!MaxMinType".~~ 
     252 
     253~~ ST_AsJPEG(raster, "GRAYSCALE", min, max, text) - convert only band 1 with quality = 75~~ 
     254 
     255~~ ST_AsJPEG(raster, "GRAYSCALE", integer, min, max, text) - convert only band 1 with specified quality~~ 
     256 
     257~~ ST_AsJPEG(raster, integer, "GRAYSCALE", min, max, text) - allow specifying the band number to convert~~ 
     258 
     259~~ ST_AsJPEG(raster, integer, "GRAYSCALE", integer, min, max, text) - allow specifying the band number to convert and the quality~~ 
    257260 
    258261---- 
    … …  
    263266compression=[JPEG/LZW/PACKBITS/DEFLATE/CCITTRLE/CCITTFAX3/CCITTFAX4/NONE]: Set the type of compression to use. None is the default. The CCITT compression should only be used with 1bit (NBITS=1) data. JPEG should only be used with Byte data. When using JPEG add a number specifying the quality. 75 is the default. e.g. ST_AsTIFF(raster, "JPEG60") (copied from http://www.gdal.org/frmt_gtiff.html) 
    264267 
    265 Bborie: A proposed implementation of the ST_AsTIFF functions. 
     268A proposed implementation of the ST_AsTIFF functions. 
    266269 
    267270The TIFF format is probably the most robust available for converting rasters to GDAL rasters. Not only does it support all PostGIS Raster pixel types, it also provides plenty of creation options and possibly no issues with the number of bands. The only limitation found is that there can only be one NODATA value for all bands.