[Geoserver-users] Problem displaying 4-band raster images

GeoServer GeoServer User
1

Hi,
Thought it would be sensible to make a new post from this.

Basically, GeoServer treats 4-band images rather strangely. Below are two
images, the first one displays the 4 band image, the second shows the same
image with the 4th band removed with GDAL. It seems as thought GeoServer
treats the 4th band as alpha.

Has any work started on getting RasterSymbolizer to work with GeoServer?

Thanks!
Jon.

http://www.nabble.com/file/p15183090/4band.jpg
http://www.nabble.com/file/p15183090/3band.jpg
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2

Jon Britton ha scritto:

Hi,
Thought it would be sensible to make a new post from this.

Basically, GeoServer treats 4-band images rather strangely. Below are two
images, the first one displays the 4 band image, the second shows the same
image with the 4th band removed with GDAL. It seems as thought GeoServer
treats the 4th band as alpha.

Has any work started on getting RasterSymbolizer to work with GeoServer?

Yes, there is a branch with work underway, and we should start merging stuff back after the 1.6.0 release, thought it's not clear whether
the changes will be against 1.6.x or trunk...

Simone, Chris, what are the plans on this one?

Cheers
Andrea

3

Is this problem I'm getting simply a bug or is there a reason for GeoServer
doing this with the 4th band? Or maybe it's to do with the information
stored in the GeoTiff? I know GDAL sometimes says a band is the alpha
channel.

Cheers,
Jon

aaime wrote:

Jon Britton ha scritto:

Hi,
Thought it would be sensible to make a new post from this.

Basically, GeoServer treats 4-band images rather strangely. Below are two
images, the first one displays the 4 band image, the second shows the
same
image with the 4th band removed with GDAL. It seems as thought GeoServer
treats the 4th band as alpha.

Has any work started on getting RasterSymbolizer to work with GeoServer?

Yes, there is a branch with work underway, and we should start merging
stuff back after the 1.6.0 release, thought it's not clear whether
the changes will be against 1.6.x or trunk...

Simone, Chris, what are the plans on this one?

Cheers
Andrea

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4

Jon,

As you probably know, RasterSymbolizer allows you to pull out specific
bands and indicate them to be put into the red, green and blue color
bands.

As for displaying a 4-band image...in my **very limited** experience
most folks work with 4-band images by mapping some set of the bands into
the rgba color-space. If the fourth band is being treated as alpha,
it's probably because that's the default implementation of a
non-RasterSymbolizer-enhanced geoserver.

If you're building geotools/geoserver from source, you can apply the
patch at http://jira.codehaus.org/browse/GEOT-1691 to the latest
geotools 2.4.x checkout, then rebuild geotools and geoserver, and you'll
have rastersymbolizer support (preliminary! May have bugs!) built into
your geoserver. That might help you to render your image better.

Alternatively, you can wait till GT-2.4.0/GS-1.6.0 goes out the door and
then I'll be applying that patch to 2.4.x and it will show up in
geoserver 1.6.x nightly builds. Also, there's some hope that an
improved version of that code will be landing on geotools trunk sometime
soon (in the next week/weeks?) which will make rastersymbolizer support
available on geoserver 1.7.x (trunk) nightly snapshots.

If you get the patch applied to GT 2.4.x, let us know if you find bugs.
We can try to track them down, or at least get them fixed in the trunk
version when it shows up.

--saul

On Wed, 2008-01-30 at 07:48 -0800, Jon Britton wrote:

Is this problem I'm getting simply a bug or is there a reason for GeoServer
doing this with the 4th band? Or maybe it's to do with the information
stored in the GeoTiff? I know GDAL sometimes says a band is the alpha
channel.

Cheers,
Jon

aaime wrote:
>
> Jon Britton ha scritto:
>> Hi,
>> Thought it would be sensible to make a new post from this.
>>
>> Basically, GeoServer treats 4-band images rather strangely. Below are two
>> images, the first one displays the 4 band image, the second shows the
>> same
>> image with the 4th band removed with GDAL. It seems as thought GeoServer
>> treats the 4th band as alpha.
>>
>> Has any work started on getting RasterSymbolizer to work with GeoServer?
>
> Yes, there is a branch with work underway, and we should start merging
> stuff back after the 1.6.0 release, thought it's not clear whether
> the changes will be against 1.6.x or trunk...
>
> Simone, Chris, what are the plans on this one?
>
> Cheers
> Andrea
>
> -------------------------------------------------------------------------
> This SF.net email is sponsored by: Microsoft
> Defy all challenges. Microsoft(R) Visual Studio 2008.
> http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/
> _______________________________________________
> Geoserver-users mailing list
> Geoserver-users@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/geoserver-users
>
>

5

Thanks for the help.

I think I will have to leave it for now, I don't really have too much time.
I might have a look at some point over the next week or so. Really I was
just questioning whether this default behaviour of treating band 4 as the
alpha channel is really a good idea, since I would have thought multi-band
raster data does not need an alpha channel.

Anyway, thanks for your reply. I look forward to when I can get support for
RasterSymbolizer since for my purposes it would be very useful indeed!
Exciting times ahead :wink:

Thanks,
Jon

sjf8 wrote:

Jon,

As you probably know, RasterSymbolizer allows you to pull out specific
bands and indicate them to be put into the red, green and blue color
bands.

As for displaying a 4-band image...in my **very limited** experience
most folks work with 4-band images by mapping some set of the bands into
the rgba color-space. If the fourth band is being treated as alpha,
it's probably because that's the default implementation of a
non-RasterSymbolizer-enhanced geoserver.

If you're building geotools/geoserver from source, you can apply the
patch at http://jira.codehaus.org/browse/GEOT-1691 to the latest
geotools 2.4.x checkout, then rebuild geotools and geoserver, and you'll
have rastersymbolizer support (preliminary! May have bugs!) built into
your geoserver. That might help you to render your image better.

Alternatively, you can wait till GT-2.4.0/GS-1.6.0 goes out the door and
then I'll be applying that patch to 2.4.x and it will show up in
geoserver 1.6.x nightly builds. Also, there's some hope that an
improved version of that code will be landing on geotools trunk sometime
soon (in the next week/weeks?) which will make rastersymbolizer support
available on geoserver 1.7.x (trunk) nightly snapshots.

If you get the patch applied to GT 2.4.x, let us know if you find bugs.
We can try to track them down, or at least get them fixed in the trunk
version when it shows up.

--saul

On Wed, 2008-01-30 at 07:48 -0800, Jon Britton wrote:

Is this problem I'm getting simply a bug or is there a reason for
GeoServer
doing this with the 4th band? Or maybe it's to do with the information
stored in the GeoTiff? I know GDAL sometimes says a band is the alpha
channel.

Cheers,
Jon

aaime wrote:
>
> Jon Britton ha scritto:
>> Hi,
>> Thought it would be sensible to make a new post from this.
>>
>> Basically, GeoServer treats 4-band images rather strangely. Below are
two
>> images, the first one displays the 4 band image, the second shows the
>> same
>> image with the 4th band removed with GDAL. It seems as thought
GeoServer
>> treats the 4th band as alpha.
>>
>> Has any work started on getting RasterSymbolizer to work with
GeoServer?
>
> Yes, there is a branch with work underway, and we should start merging
> stuff back after the 1.6.0 release, thought it's not clear whether
> the changes will be against 1.6.x or trunk...
>
> Simone, Chris, what are the plans on this one?
>
> Cheers
> Andrea
>
>
-------------------------------------------------------------------------
> This SF.net email is sponsored by: Microsoft
> Defy all challenges. Microsoft(R) Visual Studio 2008.
> http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/
> _______________________________________________
> Geoserver-users mailing list
> Geoserver-users@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/geoserver-users
>
>

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6

Just out of curiosity, how would you like to display the 4-band data?

-----Original Message-----
From: geoserver-users-bounces@lists.sourceforge.net on behalf of Jon Britton
Sent: Wed 1/30/2008 12:12 PM
To: geoserver-users@lists.sourceforge.net
Subject: Re: [Geoserver-users] Problem displaying 4-band raster images

Thanks for the help.

I think I will have to leave it for now, I don’t really have too much time.
I might have a look at some point over the next week or so. Really I was
just questioning whether this default behaviour of treating band 4 as the
alpha channel is really a good idea, since I would have thought multi-band
raster data does not need an alpha channel.

Anyway, thanks for your reply. I look forward to when I can get support for
RasterSymbolizer since for my purposes it would be very useful indeed!
Exciting times ahead :wink:

Thanks,
Jon

sjf8 wrote:

Jon,

As you probably know, RasterSymbolizer allows you to pull out specific
bands and indicate them to be put into the red, green and blue color
bands.

As for displaying a 4-band image…in my very limited experience
most folks work with 4-band images by mapping some set of the bands into
the rgba color-space. If the fourth band is being treated as alpha,
it’s probably because that’s the default implementation of a
non-RasterSymbolizer-enhanced geoserver.

If you’re building geotools/geoserver from source, you can apply the
patch at http://jira.codehaus.org/browse/GEOT-1691 to the latest
geotools 2.4.x checkout, then rebuild geotools and geoserver, and you’ll
have rastersymbolizer support (preliminary! May have bugs!) built into
your geoserver. That might help you to render your image better.

Alternatively, you can wait till GT-2.4.0/GS-1.6.0 goes out the door and
then I’ll be applying that patch to 2.4.x and it will show up in
geoserver 1.6.x nightly builds. Also, there’s some hope that an
improved version of that code will be landing on geotools trunk sometime
soon (in the next week/weeks?) which will make rastersymbolizer support
available on geoserver 1.7.x (trunk) nightly snapshots.

If you get the patch applied to GT 2.4.x, let us know if you find bugs.
We can try to track them down, or at least get them fixed in the trunk
version when it shows up.

–saul

On Wed, 2008-01-30 at 07:48 -0800, Jon Britton wrote:

Is this problem I’m getting simply a bug or is there a reason for
GeoServer
doing this with the 4th band? Or maybe it’s to do with the information
stored in the GeoTiff? I know GDAL sometimes says a band is the alpha
channel.

Cheers,
Jon

aaime wrote:

Jon Britton ha scritto:

Hi,
Thought it would be sensible to make a new post from this.

Basically, GeoServer treats 4-band images rather strangely. Below are
two
images, the first one displays the 4 band image, the second shows the
same
image with the 4th band removed with GDAL. It seems as thought
GeoServer
treats the 4th band as alpha.

Has any work started on getting RasterSymbolizer to work with
GeoServer?

Yes, there is a branch with work underway, and we should start merging
stuff back after the 1.6.0 release, thought it’s not clear whether
the changes will be against 1.6.x or trunk…

Simone, Chris, what are the plans on this one?

Cheers
Andrea

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7

As some kind of false colour composite. The kind would vary depending on
what the user wants (ideally). The most basic I would require is the
following, which nicely displays vegetation:

Red: band 3 (Near infra-red band)
Green: band 2 (red band)
Blue: band 1 (green band)

I know that the SLD ChannelSelect tag would allow me to do this. The thing
is about the SPOT data I have is that there is no blue band. There are more
complex composities which would allow the data to be displayed in a more
'natural' way to make up for the lack of a blue band, eg:

Red: band2
Green: (3 * band1 + band3)/4
Blue: (3 * band1 - band3)/4

I'm not sure if this would supported by SLDs but is quite a common method of
displaying this sort of data.

Thanks,
Jon

Roger.Andre wrote:

Just out of curiosity, how would you like to display the 4-band data?

-----Original Message-----
From: geoserver-users-bounces@lists.sourceforge.net on behalf of Jon
Britton
Sent: Wed 1/30/2008 12:12 PM
To: geoserver-users@lists.sourceforge.net
Subject: Re: [Geoserver-users] Problem displaying 4-band raster images

Thanks for the help.

I think I will have to leave it for now, I don't really have too much
time.
I might have a look at some point over the next week or so. Really I was
just questioning whether this default behaviour of treating band 4 as the
alpha channel is really a good idea, since I would have thought multi-band
raster data does not need an alpha channel.

Anyway, thanks for your reply. I look forward to when I can get support
for
RasterSymbolizer since for my purposes it would be very useful indeed!
Exciting times ahead :wink:

Thanks,
Jon

sjf8 wrote:

Jon,

As you probably know, RasterSymbolizer allows you to pull out specific
bands and indicate them to be put into the red, green and blue color
bands.

As for displaying a 4-band image...in my **very limited** experience
most folks work with 4-band images by mapping some set of the bands into
the rgba color-space. If the fourth band is being treated as alpha,
it's probably because that's the default implementation of a
non-RasterSymbolizer-enhanced geoserver.

If you're building geotools/geoserver from source, you can apply the
patch at http://jira.codehaus.org/browse/GEOT-1691 to the latest
geotools 2.4.x checkout, then rebuild geotools and geoserver, and you'll
have rastersymbolizer support (preliminary! May have bugs!) built into
your geoserver. That might help you to render your image better.

Alternatively, you can wait till GT-2.4.0/GS-1.6.0 goes out the door and
then I'll be applying that patch to 2.4.x and it will show up in
geoserver 1.6.x nightly builds. Also, there's some hope that an
improved version of that code will be landing on geotools trunk sometime
soon (in the next week/weeks?) which will make rastersymbolizer support
available on geoserver 1.7.x (trunk) nightly snapshots.

If you get the patch applied to GT 2.4.x, let us know if you find bugs.
We can try to track them down, or at least get them fixed in the trunk
version when it shows up.

--saul

On Wed, 2008-01-30 at 07:48 -0800, Jon Britton wrote:

Is this problem I'm getting simply a bug or is there a reason for
GeoServer
doing this with the 4th band? Or maybe it's to do with the information
stored in the GeoTiff? I know GDAL sometimes says a band is the alpha
channel.

Cheers,
Jon

aaime wrote:
>
> Jon Britton ha scritto:
>> Hi,
>> Thought it would be sensible to make a new post from this.
>>
>> Basically, GeoServer treats 4-band images rather strangely. Below are
two
>> images, the first one displays the 4 band image, the second shows the
>> same
>> image with the 4th band removed with GDAL. It seems as thought
GeoServer
>> treats the 4th band as alpha.
>>
>> Has any work started on getting RasterSymbolizer to work with
GeoServer?
>
> Yes, there is a branch with work underway, and we should start merging
> stuff back after the 1.6.0 release, thought it's not clear whether
> the changes will be against 1.6.x or trunk...
>
> Simone, Chris, what are the plans on this one?
>
> Cheers
> Andrea
>
>
-------------------------------------------------------------------------
> This SF.net email is sponsored by: Microsoft
> Defy all challenges. Microsoft(R) Visual Studio 2008.
> http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/
> _______________________________________________
> Geoserver-users mailing list
> Geoserver-users@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/geoserver-users
>
>

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8

Jon Britton ha scritto:

As some kind of false colour composite. The kind would vary depending
on what the user wants (ideally). The most basic I would require is
the following, which nicely displays vegetation:

Red: band 3 (Near infra-red band) Green: band 2 (red band) Blue: band
1 (green band)

I know that the SLD ChannelSelect tag would allow me to do this. The
thing is about the SPOT data I have is that there is no blue band.
There are more complex composities which would allow the data to be
displayed in a more 'natural' way to make up for the lack of a blue
band, eg:

Red: band2 Green: (3 * band1 + band3)/4 Blue: (3 * band1 - band3)/4

I'm not sure if this would supported by SLDs but is quite a common
method of displaying this sort of data.

Jon,
the SLD standard is published and can be looked at, it's here:
http://portal.opengeospatial.org/files/?artifact_id=1188

I've looked into it and it seems the kind of band combining you're
looking for is not taken into consideration. It has to be done
offline using external software (I bet GRASS can do it).

As for other softwares, I really don't know how they are displaying
the image, maybe there's some tiff tag that provides enough information
for a correct display and we're ignoring it... impossible to say without
a sample of the image.

Cheers
Andrea

9

aaime wrote:

I've looked into it and it seems the kind of band combining you're
looking for is not taken into consideration. It has to be done
offline using external software (I bet GRASS can do it).

Do you mean the more complex example I mentioned? I'm pretty sure the SLD
specification allows you to specify which bands in the image correspond the
which band in the output image, which is that is required for the most basic
false colour composite.

As for how it's working currently - how come GeoServer does not completely
ignore band 4? This would seem like a more sensible default behaviour. I
will try and get a sample image if you like.

Cheers,
Jon

aaime wrote:

As for other softwares, I really don't know how they are displaying
the image, maybe there's some tiff tag that provides enough information
for a correct display and we're ignoring it... impossible to say without
a sample of the image.

Cheers
Andrea

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10

Jon Britton ha scritto:

aaime wrote:

I've looked into it and it seems the kind of band combining you're
looking for is not taken into consideration. It has to be done
offline using external software (I bet GRASS can do it).

Do you mean the more complex example I mentioned? I'm pretty sure the SLD
specification allows you to specify which bands in the image correspond the
which band in the output image, which is that is required for the most basic
false colour composite.

Yes, that is supported by SLD... wheter it's supported by the raster symbolizer branch, that I don't know... only Simone, Alessio or Saul can
answer this... guys??

As for how it's working currently - how come GeoServer does not completely
ignore band 4? This would seem like a more sensible default behaviour. I
will try and get a sample image if you like.

I disagree. I have various images with alpha channel as the fourth band,
I would not be happy if that was ignored. The default is thought for photographic images taken in the visible spectrum, the current default are ok for this kind of application.
I hope raster symbolizer can support your use case, but unfortunately
I still haven't had the time to look at the branch with raster
symbolizer support so I cannot answer your question.

Cheers
Andrea

11

Hi Jon,

Not sure is you want to create a new set of images, but gdal_translate
can be used to create a 3-band image like you describe in your first
example. It's been a little while since I've done this, but I'm pretty
sure that if you took a 4-band image that was currently ordered like
this:

Band | Color
------------
1 Red
2 Green
3 Blue
4 IR

You can create a 3-band false color image that uses the IR band like
this:

gdal_translate -b 4 -b 1 -b 2 <in_file> <out_file>

I know what you mean about the lack of blue, its a challenge to make
pseudo-natural color look right.
--
Roger

-----Original Message-----
From: geoserver-users-bounces@lists.sourceforge.net
[mailto:geoserver-users-bounces@lists.sourceforge.net] On Behalf Of Jon
Britton
Sent: Thursday, January 31, 2008 1:19 AM
To: geoserver-users@lists.sourceforge.net
Subject: Re: [Geoserver-users] Problem displaying 4-band raster images

As some kind of false colour composite. The kind would vary depending on
what the user wants (ideally). The most basic I would require is the
following, which nicely displays vegetation:

Red: band 3 (Near infra-red band)
Green: band 2 (red band)
Blue: band 1 (green band)

I know that the SLD ChannelSelect tag would allow me to do this. The
thing is about the SPOT data I have is that there is no blue band. There
are more complex composities which would allow the data to be displayed
in a more 'natural' way to make up for the lack of a blue band, eg:

Red: band2
Green: (3 * band1 + band3)/4
Blue: (3 * band1 - band3)/4

I'm not sure if this would supported by SLDs but is quite a common
method of displaying this sort of data.

Thanks,
Jon

Roger.Andre wrote:

Just out of curiosity, how would you like to display the 4-band data?

-----Original Message-----
From: geoserver-users-bounces@lists.sourceforge.net on behalf of Jon
Britton
Sent: Wed 1/30/2008 12:12 PM
To: geoserver-users@lists.sourceforge.net
Subject: Re: [Geoserver-users] Problem displaying 4-band raster images

Thanks for the help.

I think I will have to leave it for now, I don't really have too much
time.
I might have a look at some point over the next week or so. Really I
was just questioning whether this default behaviour of treating band 4

as the alpha channel is really a good idea, since I would have thought

multi-band raster data does not need an alpha channel.

Anyway, thanks for your reply. I look forward to when I can get
support for RasterSymbolizer since for my purposes it would be very
useful indeed!
Exciting times ahead :wink:

Thanks,
Jon

sjf8 wrote:

Jon,

As you probably know, RasterSymbolizer allows you to pull out
specific bands and indicate them to be put into the red, green and
blue color bands.

As for displaying a 4-band image...in my **very limited** experience
most folks work with 4-band images by mapping some set of the bands
into the rgba color-space. If the fourth band is being treated as
alpha, it's probably because that's the default implementation of a
non-RasterSymbolizer-enhanced geoserver.

If you're building geotools/geoserver from source, you can apply the
patch at http://jira.codehaus.org/browse/GEOT-1691 to the latest
geotools 2.4.x checkout, then rebuild geotools and geoserver, and
you'll have rastersymbolizer support (preliminary! May have bugs!)
built into your geoserver. That might help you to render your image

better.

Alternatively, you can wait till GT-2.4.0/GS-1.6.0 goes out the door
and then I'll be applying that patch to 2.4.x and it will show up in
geoserver 1.6.x nightly builds. Also, there's some hope that an
improved version of that code will be landing on geotools trunk
sometime soon (in the next week/weeks?) which will make
rastersymbolizer support available on geoserver 1.7.x (trunk) nightly

snapshots.

If you get the patch applied to GT 2.4.x, let us know if you find

bugs.

We can try to track them down, or at least get them fixed in the
trunk version when it shows up.

--saul

On Wed, 2008-01-30 at 07:48 -0800, Jon Britton wrote:

Is this problem I'm getting simply a bug or is there a reason for
GeoServer doing this with the 4th band? Or maybe it's to do with the

information stored in the GeoTiff? I know GDAL sometimes says a band

is the alpha channel.

Cheers,
Jon

aaime wrote:
>
> Jon Britton ha scritto:
>> Hi,
>> Thought it would be sensible to make a new post from this.
>>
>> Basically, GeoServer treats 4-band images rather strangely. Below

>> are
two
>> images, the first one displays the 4 band image, the second shows

>> the same image with the 4th band removed with GDAL. It seems as
>> thought
GeoServer
>> treats the 4th band as alpha.
>>
>> Has any work started on getting RasterSymbolizer to work with
GeoServer?
>
> Yes, there is a branch with work underway, and we should start
> merging stuff back after the 1.6.0 release, thought it's not clear

> whether the changes will be against 1.6.x or trunk...
>
> Simone, Chris, what are the plans on this one?
>
> Cheers
> Andrea
>
>
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