[Qgis-user] Generating black white from RGB landsat using Raster Map calculator?

[Chas Sheen]

Mike,

So everything in the capture below of the Raster calculator should work? I cannot find any output.

I’m in Perth, Australia so home now and away from the office and QGIS, but would like to get it working tomorrow.

How do apply a grayscale to a raster? As I said, I’m new to QGIS

Chas Sheen

 

From: Micha Silver [mailto:tsvibar at gmail.com] 
Sent: Wednesday, January 17, 2018 8:39 PM
To: Chas Sheen <chassheengeo at gmail.com>; qgis-user at lists.osgeo.org
Subject: Re: [Qgis-user] Generating black white from RGB landsat using Raster Map calculator?

 

Hello Chas

On 01/17/2018 01:52 PM, Chas Sheen wrote:

Richard,

 

I should have made my initial query clearer.

I am trying to output a black and white geotiff.

It's still not clear what you are asking. AFAIK, there's no such thing as a "black and white geotiff". You can apply any color table you want to any raster. You can apply a gray scale to any of the landsat bands.

 

If you are trying to create a new raster from the three RGB bands using some expression, that should work. You can use either of three tools: the built in QGIS raster calculator, or thru the Processing toolbox there's SAGA Raster calculus and the GRASS module r.mapcalculator. 

 

Again, none of this has anything to do with coloring. After running the raster calculator, you can color the result with a gray scale color table, a red color table, or any other color ramp you choose.

 

 

Have split the original (landsat) image into RGB images.

When I apply the expression in the capture below, and hit run, nothing is saved to the results directory.

I’m assuming that my expression or something else in the raster calculator is wrong?

The final product that I’m after is a xyz grid where z is the black-white amplitude…which I think should be relatively easy (?) once I have the black-white image.

After you running the calculator expression, then you can save the result in many formats, including gridded XYZ, ArcINFO ASCII, or many others, using the gdal_translate tool. This is under the Raster->Conversion menu.

 

 

Chas Sheen

0448017282

 

From: Richard McDonnell [mailto:richard.mcdonnell at opw.ie] 
Sent: Wednesday, January 17, 2018 7:13 PM
To: Chas Sheen  <mailto:chassheengeo at gmail.com> <chassheengeo at gmail.com>; qgis-user at lists.osgeo.org <mailto:qgis-user at lists.osgeo.org> 
Subject: Re: [Qgis-user] Generating black white from RGB landsat using Raster Map calculator?

 

Chas,
Two options for splitting RGB into separate images in QGIS.

1.	Semi-Automatic Classification Plugin, Preprocessing, Split Raster Bands
2.	Grass r-rgb (Processing Toolbox)

Any one of these tools will split the Raster for you easy enough
Regards,

Richard

On 17/01/2018 00:48, Chas Sheen wrote:

I split the image into R, G, B

Worked out in QGIS wher the Raster map calculator is.

Run...several times

No result foud in Results Directory. It runs quickly then refreshes inputs and logs to blanks.

I'm new to QGIS....so have probably left out something basic.

Any clues

 









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Richard McDonnell
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OPW FRM Data Management
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Micha Silver
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Sde Boker, Remote Sensing Lab
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