[Qgis-user] Four band raster displaying funny
Hi List, I've got a 4 band raster aerial photography (RGBI) that comprises lots of tiles. I've merged some of the tiles together with: gdal_merge -o 1.tif -of GTiff -co TILED=YES -co BIGTIFF=YES -co COMPRESS=JPEG -co JPEG_QUALITY=50 -co BLOCKXSIZE=512 -co BLOCKYSIZE=512 --optfile tiff_list.txt But the resultant file looks funny in QGIS. This is what the source file looks like (correct): [image: Inline images 1] This is what the merged file looks like (wrong): [image: Inline images 2] All the shadows are a whitey colour. This doesn't happen with 3-band (RGB) images. I've tried comparing individual bands; they all look different in the 4-band. However, if I open the four-band in ArcGIS, it looks fine (both source and original). Anyone know what's going on? Is it a QGIS bug or is it doing something smart; I can't see anything odd going on with symbology. Thanks, Jonathan -- This transmission is intended for the named addressee(s) only and may contain sensitive or protectively marked material up to RESTRICTED and should be handled accordingly. Unless you are the named addressee (or authorised to receive it for the addressee) you may not copy or use it, or disclose it to anyone else. If you have received this transmission in error please notify the sender immediately. All email traffic sent to or from us, including without limitation all GCSX traffic, may be subject to recording and/or monitoring in accordance with relevant legislation. image.pngimage.png___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] Four band raster displaying funny
Jonathan Moules jonathanmoules@... writes: Hi List, I've got a 4 band raster aerial photography (RGBI) that comprises lots of tiles. I've merged some of the tiles together with: gdal_merge -o 1.tif -of GTiff -co TILED=YES -co BIGTIFF=YES -co COMPRESS=JPEG -co JPEG_QUALITY=50 -co BLOCKXSIZE=512 -co BLOCKYSIZE=512 --optfile tiff_list.txt Are you sure that after running that command you have a 4-band image? I have believed that JPEG compression can be used only for 1- or 3-band images. What does gdalinfo report about your image? I would have a try by using LZW or deflate compression and annex for example a screenshot about the settings you have been using for selecting the bands and adjusting histogram stretching etc. -Jukka Rahkonen- ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] Four band raster displaying funny
Hi Jonathan, Is it possible that QGIS is using the infrared band as an alpha channel? This might explain the whitening effect, especially in non-vegetated areas. I would check the Layer properties Transparency tab to see whether anything is set as the transparency band. If it is, you could override QGIS by setting a default style. Cheers, Andy On 02/12/2013 11:53, Jonathan Moules wrote: Hi List, I've got a 4 band raster aerial photography (RGBI) that comprises lots of tiles. I've merged some of the tiles together with: gdal_merge -o 1.tif -of GTiff -co TILED=YES -co BIGTIFF=YES -co COMPRESS=JPEG -co JPEG_QUALITY=50 -co BLOCKXSIZE=512 -co BLOCKYSIZE=512 --optfile tiff_list.txt But the resultant file looks funny in QGIS. This is what the source file looks like (correct): This is what the merged file looks like (wrong): All the shadows are a whitey colour. This doesn't happen with 3-band (RGB) images. I've tried comparing individual bands; they all look different in the 4-band. However, if I open the four-band in ArcGIS, it looks fine (both source and original). Anyone know what's going on? Is it a QGIS bug or is it doing something "smart"; I can't see anything odd going on with symbology. Thanks, Jonathan This transmission is intended for the named addressee(s) only and may contain sensitive or protectively marked material up to RESTRICTED and should be handled accordingly. Unless you are the named addressee (or authorised to receive it for the addressee) you may not copy or use it, or disclose it to anyone else. If you have received this transmission in error please notify the sender immediately. All email traffic sent to or from us, including without limitation all GCSX traffic, may be subject to recording and/or monitoring in accordance with relevant legislation. ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user -- Andy Harfoot GeoData Institute University of Southampton Southampton SO17 1BJ Tel: +44 (0)23 8059 2719 Fax: +44 (0)23 8059 2849 www.geodata.soton.ac.uk ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] Four band raster displaying funny
PS. gdalwarp offers more flexibility when mosaicing rasters, and is better at memory management. I have just noticed that in GDAL 1.10 and above there is an gdalwarp option -setci that 'Sets the color interpretation of the bands of the target dataset from the source dataset'. This could be used to remove the assignment of the alpha channel to the IR band on merging. Sadly there isn't an example of its usage! Cheers, Andy On 02/12/2013 11:53, Jonathan Moules wrote: Hi List, I've got a 4 band raster aerial photography (RGBI) that comprises lots of tiles. I've merged some of the tiles together with: gdal_merge -o 1.tif -of GTiff -co TILED=YES -co BIGTIFF=YES -co COMPRESS=JPEG -co JPEG_QUALITY=50 -co BLOCKXSIZE=512 -co BLOCKYSIZE=512 --optfile tiff_list.txt But the resultant file looks funny in QGIS. This is what the source file looks like (correct): This is what the merged file looks like (wrong): All the shadows are a whitey colour. This doesn't happen with 3-band (RGB) images. I've tried comparing individual bands; they all look different in the 4-band. However, if I open the four-band in ArcGIS, it looks fine (both source and original). Anyone know what's going on? Is it a QGIS bug or is it doing something "smart"; I can't see anything odd going on with symbology. Thanks, Jonathan This transmission is intended for the named addressee(s) only and may contain sensitive or protectively marked material up to RESTRICTED and should be handled accordingly. Unless you are the named addressee (or authorised to receive it for the addressee) you may not copy or use it, or disclose it to anyone else. If you have received this transmission in error please notify the sender immediately. All email traffic sent to or from us, including without limitation all GCSX traffic, may be subject to recording and/or monitoring in accordance with relevant legislation. ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user -- Andy Harfoot GeoData Institute University of Southampton Southampton SO17 1BJ Tel: +44 (0)23 8059 2719 Fax: +44 (0)23 8059 2849 www.geodata.soton.ac.uk ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] Four band raster displaying funny
Hi Andy, Yep, that was it. I didn't know QGIS could do that; another good example of software trying to be smart and confusing the poor user. :-) I didn't know gdalwarp could do mosaicing too. I'll have to test it. I'll ask on the gdal list if I want to try the -setci parameter. Many thanks! Jonathan On 2 December 2013 15:48, Andrew Harfoot a...@geodata.soton.ac.uk wrote: PS. gdalwarp offers more flexibility when mosaicing rasters, and is better at memory management. I have just noticed that in GDAL 1.10 and above there is an gdalwarp option -setci that 'Sets the color interpretation of the bands of the target dataset from the source dataset'. This could be used to remove the assignment of the alpha channel to the IR band on merging. Sadly there isn't an example of its usage! Cheers, Andy On 02/12/2013 11:53, Jonathan Moules wrote: Hi List, I've got a 4 band raster aerial photography (RGBI) that comprises lots of tiles. I've merged some of the tiles together with: gdal_merge -o 1.tif -of GTiff -co TILED=YES -co BIGTIFF=YES -co COMPRESS=JPEG -co JPEG_QUALITY=50 -co BLOCKXSIZE=512 -co BLOCKYSIZE=512 --optfile tiff_list.txt But the resultant file looks funny in QGIS. This is what the source file looks like (correct): [image: Inline images 1] This is what the merged file looks like (wrong): [image: Inline images 2] All the shadows are a whitey colour. This doesn't happen with 3-band (RGB) images. I've tried comparing individual bands; they all look different in the 4-band. However, if I open the four-band in ArcGIS, it looks fine (both source and original). Anyone know what's going on? Is it a QGIS bug or is it doing something smart; I can't see anything odd going on with symbology. Thanks, Jonathan This transmission is intended for the named addressee(s) only and may contain sensitive or protectively marked material up to RESTRICTED and should be handled accordingly. Unless you are the named addressee (or authorised to receive it for the addressee) you may not copy or use it, or disclose it to anyone else. If you have received this transmission in error please notify the sender immediately. All email traffic sent to or from us, including without limitation all GCSX traffic, may be subject to recording and/or monitoring in accordance with relevant legislation. ___ Qgis-user mailing listQgis-user@lists.osgeo.orghttp://lists.osgeo.org/mailman/listinfo/qgis-user -- Andy Harfoot GeoData Institute University of Southampton Southampton SO17 1BJ Tel: +44 (0)23 8059 2719 Fax: +44 (0)23 8059 2849 www.geodata.soton.ac.uk ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user -- This transmission is intended for the named addressee(s) only and may contain sensitive or protectively marked material up to RESTRICTED and should be handled accordingly. Unless you are the named addressee (or authorised to receive it for the addressee) you may not copy or use it, or disclose it to anyone else. If you have received this transmission in error please notify the sender immediately. All email traffic sent to or from us, including without limitation all GCSX traffic, may be subject to recording and/or monitoring in accordance with relevant legislation. ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] Four band raster displaying funny
I think QGIS is innocent in this - if a band is set as an alpha channel then it should be handled as such by default in a viewer (so mark down Arc for not using the alpha information!). GDAL is the culprit as it is adding the alpha interpretation without being prompted. I have just replicated this with some RGBI imagery myself: prior to passing through GDAL's hands the IR band is present, but isn't interpreted as an alpha channel. I can't get the -setci switch to do anything though :( Cheers, Andy On 02/12/2013 16:00, Jonathan Moules wrote: Hi Andy, Yep, that was it. I didn't know QGIS could do that; another good example of software trying to be smart and confusing the poor user. :-) I didn't know gdalwarp could do mosaicing too. I'll have to test it. I'll ask on the gdal list if I want to try the -setci parameter. Many thanks! Jonathan On 2 December 2013 15:48, Andrew Harfoot a...@geodata.soton.ac.uk mailto:a...@geodata.soton.ac.uk wrote: PS. gdalwarp offers more flexibility when mosaicing rasters, and is better at memory management. I have just noticed that in GDAL 1.10 and above there is an gdalwarp option -setci that 'Sets the color interpretation of the bands of the target dataset from the source dataset'. This could be used to remove the assignment of the alpha channel to the IR band on merging. Sadly there isn't an example of its usage! Cheers, Andy On 02/12/2013 11:53, Jonathan Moules wrote: Hi List, I've got a 4 band raster aerial photography (RGBI) that comprises lots of tiles. I've merged some of the tiles together with: gdal_merge -o 1.tif -of GTiff -co TILED=YES -co BIGTIFF=YES -co COMPRESS=JPEG -co JPEG_QUALITY=50 -co BLOCKXSIZE=512 -co BLOCKYSIZE=512 --optfile tiff_list.txt But the resultant file looks funny in QGIS. This is what the source file looks like (correct): Inline images 1 This is what the merged file looks like (wrong): Inline images 2 All the shadows are a whitey colour. This doesn't happen with 3-band (RGB) images. I've tried comparing individual bands; they all look different in the 4-band. However, if I open the four-band in ArcGIS, it looks fine (both source and original). Anyone know what's going on? Is it a QGIS bug or is it doing something smart; I can't see anything odd going on with symbology. Thanks, Jonathan This transmission is intended for the named addressee(s) only and may contain sensitive or protectively marked material up to RESTRICTED and should be handled accordingly. Unless you are the named addressee (or authorised to receive it for the addressee) you may not copy or use it, or disclose it to anyone else. If you have received this transmission in error please notify the sender immediately. All email traffic sent to or from us, including without limitation all GCSX traffic, may be subject to recording and/or monitoring in accordance with relevant legislation. ___ Qgis-user mailing list Qgis-user@lists.osgeo.org mailto:Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user -- Andy Harfoot GeoData Institute University of Southampton Southampton SO17 1BJ Tel:+44 (0)23 8059 2719 tel:%2B44%20%280%2923%208059%202719 Fax:+44 (0)23 8059 2849 tel:%2B44%20%280%2923%208059%202849 www.geodata.soton.ac.uk http://www.geodata.soton.ac.uk ___ Qgis-user mailing list Qgis-user@lists.osgeo.org mailto:Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user This transmission is intended for the named addressee(s) only and may contain sensitive or protectively marked material up to RESTRICTED and should be handled accordingly. Unless you are the named addressee (or authorised to receive it for the addressee) you may not copy or use it, or disclose it to anyone else. If you have received this transmission in error please notify the sender immediately. All email traffic sent to or from us, including without limitation all GCSX traffic, may be subject to recording and/or monitoring in accordance with relevant legislation. -- Andy Harfoot GeoData Institute University of Southampton Southampton SO17 1BJ Tel: +44 (0)23 8059 2719 Fax: +44 (0)23 8059 2849 www.geodata.soton.ac.uk ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] Four band raster displaying funny
Hi Andy, I guess that makes sense. Relating to gdalwarp: - Output files by default are larger than gdal_merge. - But they can be much smaller. You have to set *both* -wm and --config GDAL_CACHEMAX - if you only set -wm, then the file is actually larger! - gdal_merge seems to do something that results in some heavy blurring when using -co PHOTOMETRIC=YCBCR - this doesn't happen with gdalwarp. So the optimal filesize for an aerial photograph is rendered with something like: gdalwarp -of GTiff -wm --config GDAL_CACHEMAX -co TILED=YES -co BIGTIFF=YES -co COMPRESS=JPEG -co JPEG_QUALITY=80 -co BLOCKXSIZE=512 -co BLOCKYSIZE=512 -co PHOTOMETRIC=YCBCR input1.tif input2.tif output.tif I've not tried the four-band stuff again; just trying to optimise by 3-band. Thanks, Jonathan On 2 December 2013 16:10, Andrew Harfoot a...@geodata.soton.ac.uk wrote: I think QGIS is innocent in this - if a band is set as an alpha channel then it should be handled as such by default in a viewer (so mark down Arc for not using the alpha information!). GDAL is the culprit as it is adding the alpha interpretation without being prompted. I have just replicated this with some RGBI imagery myself: prior to passing through GDAL's hands the IR band is present, but isn't interpreted as an alpha channel. I can't get the -setci switch to do anything though :( Cheers, Andy On 02/12/2013 16:00, Jonathan Moules wrote: Hi Andy, Yep, that was it. I didn't know QGIS could do that; another good example of software trying to be smart and confusing the poor user. :-) I didn't know gdalwarp could do mosaicing too. I'll have to test it. I'll ask on the gdal list if I want to try the -setci parameter. Many thanks! Jonathan On 2 December 2013 15:48, Andrew Harfoot a...@geodata.soton.ac.uk wrote: PS. gdalwarp offers more flexibility when mosaicing rasters, and is better at memory management. I have just noticed that in GDAL 1.10 and above there is an gdalwarp option -setci that 'Sets the color interpretation of the bands of the target dataset from the source dataset'. This could be used to remove the assignment of the alpha channel to the IR band on merging. Sadly there isn't an example of its usage! Cheers, Andy On 02/12/2013 11:53, Jonathan Moules wrote: Hi List, I've got a 4 band raster aerial photography (RGBI) that comprises lots of tiles. I've merged some of the tiles together with: gdal_merge -o 1.tif -of GTiff -co TILED=YES -co BIGTIFF=YES -co COMPRESS=JPEG -co JPEG_QUALITY=50 -co BLOCKXSIZE=512 -co BLOCKYSIZE=512 --optfile tiff_list.txt But the resultant file looks funny in QGIS. This is what the source file looks like (correct): [image: Inline images 1] This is what the merged file looks like (wrong): [image: Inline images 2] All the shadows are a whitey colour. This doesn't happen with 3-band (RGB) images. I've tried comparing individual bands; they all look different in the 4-band. However, if I open the four-band in ArcGIS, it looks fine (both source and original). Anyone know what's going on? Is it a QGIS bug or is it doing something smart; I can't see anything odd going on with symbology. Thanks, Jonathan This transmission is intended for the named addressee(s) only and may contain sensitive or protectively marked material up to RESTRICTED and should be handled accordingly. Unless you are the named addressee (or authorised to receive it for the addressee) you may not copy or use it, or disclose it to anyone else. If you have received this transmission in error please notify the sender immediately. All email traffic sent to or from us, including without limitation all GCSX traffic, may be subject to recording and/or monitoring in accordance with relevant legislation. ___ Qgis-user mailing listQgis-user@lists.osgeo.orghttp://lists.osgeo.org/mailman/listinfo/qgis-user -- Andy Harfoot GeoData Institute University of Southampton Southampton SO17 1BJ Tel: +44 (0)23 8059 2719 Fax: +44 (0)23 8059 2849 www.geodata.soton.ac.uk ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user This transmission is intended for the named addressee(s) only and may contain sensitive or protectively marked material up to RESTRICTED and should be handled accordingly. Unless you are the named addressee (or authorised to receive it for the addressee) you may not copy or use it, or disclose it to anyone else. If you have received this transmission in error please notify the sender immediately. All email traffic sent to or from us, including without limitation all GCSX traffic, may be subject to recording and/or monitoring in accordance with relevant legislation. -- Andy Harfoot GeoData Institute University of Southampton Southampton SO17 1BJ Tel: +44 (0)23 8059 2719
Re: [Qgis-user] Four band raster displaying funny
Interesting! Just found that you can override the GDAL behaviour of adding alpha interpretation (this is the default as described in the GTiff format spec here http://www.gdal.org/frmt_gtiff.html) by adding the GDAL -co command PHOTOMETRIC=RGB. Not sure how this tallys with the YCBCR colour model used by JPEG though? Cheers, Andy On 02/12/2013 16:30, Jonathan Moules wrote: Hi Andy, I guess that makes sense. Relating to gdalwarp: - Output files by default are larger than gdal_merge. - But they can be much smaller. You have to set *both* -wm and --config GDAL_CACHEMAX - if you only set -wm, then the file is actually larger! - gdal_merge seems to do something that results in some heavy blurring when using -co PHOTOMETRIC=YCBCR - this doesn't happen with gdalwarp. So the optimal filesize for an aerial photograph is rendered with something like: gdalwarp -of GTiff -wm --config GDAL_CACHEMAX -co TILED=YES -co BIGTIFF=YES -co COMPRESS=JPEG -co JPEG_QUALITY=80 -co BLOCKXSIZE=512 -co BLOCKYSIZE=512 -co PHOTOMETRIC=YCBCR input1.tif input2.tif output.tif I've not tried the four-band stuff again; just trying to optimise by 3-band. Thanks, Jonathan On 2 December 2013 16:10, Andrew Harfoot a...@geodata.soton.ac.uk mailto:a...@geodata.soton.ac.uk wrote: I think QGIS is innocent in this - if a band is set as an alpha channel then it should be handled as such by default in a viewer (so mark down Arc for not using the alpha information!). GDAL is the culprit as it is adding the alpha interpretation without being prompted. I have just replicated this with some RGBI imagery myself: prior to passing through GDAL's hands the IR band is present, but isn't interpreted as an alpha channel. I can't get the -setci switch to do anything though :( Cheers, Andy On 02/12/2013 16:00, Jonathan Moules wrote: Hi Andy, Yep, that was it. I didn't know QGIS could do that; another good example of software trying to be smart and confusing the poor user. :-) I didn't know gdalwarp could do mosaicing too. I'll have to test it. I'll ask on the gdal list if I want to try the -setci parameter. Many thanks! Jonathan On 2 December 2013 15:48, Andrew Harfoot a...@geodata.soton.ac.uk mailto:a...@geodata.soton.ac.uk wrote: PS. gdalwarp offers more flexibility when mosaicing rasters, and is better at memory management. I have just noticed that in GDAL 1.10 and above there is an gdalwarp option -setci that 'Sets the color interpretation of the bands of the target dataset from the source dataset'. This could be used to remove the assignment of the alpha channel to the IR band on merging. Sadly there isn't an example of its usage! Cheers, Andy On 02/12/2013 11:53, Jonathan Moules wrote: Hi List, I've got a 4 band raster aerial photography (RGBI) that comprises lots of tiles. I've merged some of the tiles together with: gdal_merge -o 1.tif -of GTiff -co TILED=YES -co BIGTIFF=YES -co COMPRESS=JPEG -co JPEG_QUALITY=50 -co BLOCKXSIZE=512 -co BLOCKYSIZE=512 --optfile tiff_list.txt But the resultant file looks funny in QGIS. This is what the source file looks like (correct): Inline images 1 This is what the merged file looks like (wrong): Inline images 2 All the shadows are a whitey colour. This doesn't happen with 3-band (RGB) images. I've tried comparing individual bands; they all look different in the 4-band. However, if I open the four-band in ArcGIS, it looks fine (both source and original). Anyone know what's going on? Is it a QGIS bug or is it doing something smart; I can't see anything odd going on with symbology. Thanks, Jonathan This transmission is intended for the named addressee(s) only and may contain sensitive or protectively marked material up to RESTRICTED and should be handled accordingly. Unless you are the named addressee (or authorised to receive it for the addressee) you may not copy or use it, or disclose it to anyone else. If you have received this transmission in error please notify the sender immediately. All email traffic sent to or from us, including without limitation all GCSX traffic, may be subject to recording and/or monitoring in accordance with relevant legislation. ___ Qgis-user mailing list Qgis-user@lists.osgeo.org mailto:Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user -- Andy Harfoot GeoData Institute University of Southampton Southampton SO17 1BJ
Re: [Qgis-user] Four band raster displaying funny
Further testing indicates that the same (optimal) result can be had using a combination of a vrt and gdal_translate without having to manually bother with memory management. dir /b /s *.tif tiff_list.txt REM Builds a VRT. A VRT is basically just a XML file saying what all the source tif files are. gdalbuildvrt -input_file_list tiff_list.txt file.vrt REM This is what actually does the mosaicing. gdal_translate -of GTiff -co TILED=YES -co BIGTIFF=YES -co COMPRESS=JPEG -co JPEG_QUALITY=80 -co BLOCKXSIZE=512 -co BLOCKYSIZE=512 -co PHOTOMETRIC=YCBCR file.vrt file.tif === Relating to four bands, I can confirm the PHOTOMETRIC=RGB with JPEG compression does leave the fourth band undefined: Band 1 Block=512x512 Type=Byte, ColorInterp=Red Band 2 Block=512x512 Type=Byte, ColorInterp=Green Band 3 Block=512x512 Type=Byte, ColorInterp=Blue Band 4 Block=512x512 Type=Byte, ColorInterp=Undefined The filesize is the same as setting no photometric flag. So that seems to be the solution, at least where QGIS is concerned with 4 bands. Thanks again, Jonathan On 2 December 2013 16:36, Andrew Harfoot a...@geodata.soton.ac.uk wrote: Interesting! Just found that you can override the GDAL behaviour of adding alpha interpretation (this is the default as described in the GTiff format spec here http://www.gdal.org/frmt_gtiff.html) by adding the GDAL -co command PHOTOMETRIC=RGB. Not sure how this tallys with the YCBCR colour model used by JPEG though? Cheers, Andy On 02/12/2013 16:30, Jonathan Moules wrote: Hi Andy, I guess that makes sense. Relating to gdalwarp: - Output files by default are larger than gdal_merge. - But they can be much smaller. You have to set *both* -wm and --config GDAL_CACHEMAX - if you only set -wm, then the file is actually larger! - gdal_merge seems to do something that results in some heavy blurring when using -co PHOTOMETRIC=YCBCR - this doesn't happen with gdalwarp. So the optimal filesize for an aerial photograph is rendered with something like: gdalwarp -of GTiff -wm --config GDAL_CACHEMAX -co TILED=YES -co BIGTIFF=YES -co COMPRESS=JPEG -co JPEG_QUALITY=80 -co BLOCKXSIZE=512 -co BLOCKYSIZE=512 -co PHOTOMETRIC=YCBCR input1.tif input2.tif output.tif I've not tried the four-band stuff again; just trying to optimise by 3-band. Thanks, Jonathan On 2 December 2013 16:10, Andrew Harfoot a...@geodata.soton.ac.uk wrote: I think QGIS is innocent in this - if a band is set as an alpha channel then it should be handled as such by default in a viewer (so mark down Arc for not using the alpha information!). GDAL is the culprit as it is adding the alpha interpretation without being prompted. I have just replicated this with some RGBI imagery myself: prior to passing through GDAL's hands the IR band is present, but isn't interpreted as an alpha channel. I can't get the -setci switch to do anything though :( Cheers, Andy On 02/12/2013 16:00, Jonathan Moules wrote: Hi Andy, Yep, that was it. I didn't know QGIS could do that; another good example of software trying to be smart and confusing the poor user. :-) I didn't know gdalwarp could do mosaicing too. I'll have to test it. I'll ask on the gdal list if I want to try the -setci parameter. Many thanks! Jonathan On 2 December 2013 15:48, Andrew Harfoot a...@geodata.soton.ac.ukwrote: PS. gdalwarp offers more flexibility when mosaicing rasters, and is better at memory management. I have just noticed that in GDAL 1.10 and above there is an gdalwarp option -setci that 'Sets the color interpretation of the bands of the target dataset from the source dataset'. This could be used to remove the assignment of the alpha channel to the IR band on merging. Sadly there isn't an example of its usage! Cheers, Andy On 02/12/2013 11:53, Jonathan Moules wrote: Hi List, I've got a 4 band raster aerial photography (RGBI) that comprises lots of tiles. I've merged some of the tiles together with: gdal_merge -o 1.tif -of GTiff -co TILED=YES -co BIGTIFF=YES -co COMPRESS=JPEG -co JPEG_QUALITY=50 -co BLOCKXSIZE=512 -co BLOCKYSIZE=512 --optfile tiff_list.txt But the resultant file looks funny in QGIS. This is what the source file looks like (correct): [image: Inline images 1] This is what the merged file looks like (wrong): [image: Inline images 2] All the shadows are a whitey colour. This doesn't happen with 3-band (RGB) images. I've tried comparing individual bands; they all look different in the 4-band. However, if I open the four-band in ArcGIS, it looks fine (both source and original). Anyone know what's going on? Is it a QGIS bug or is it doing something smart; I can't see anything odd going on with symbology. Thanks, Jonathan This transmission is intended for the named addressee(s) only and may contain sensitive or protectively marked material up to RESTRICTED and should be handled accordingly. Unless
Re: [Qgis-user] Four band raster displaying funny
Jonathan Moules jonathanmoules@... writes: Further testing indicates that the same (optimal) result can be had using a combination of a vrt and gdal_translate without having to manually bother with memory management. Hi, I can confirm that question is in GDAL which by default considers four band images as RGBA which is also documented in http://www.gdal.org/frmt_gtiff.html The following gdal_merge command gives a good result when source bands are in four separate tiff files and it is possible to select bands 1-2-3 for natural colour or 4-2-1 for false colour infrared in QGIS. gdal_merge.py -separate -of GTiff -co photometric=rgb -co compress=jpeg -o fourband_rgb_jpeg.tif 1.tif 2.tif 3.tif 4.tif -Jukka Rahkonen- ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user
