Changing Raster Layer Style

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(Render Type: Multiband color)
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#* Standard false color (RGB=4,3,2) makes healthy vegetation generally appear red.
 
#* Standard false color (RGB=4,3,2) makes healthy vegetation generally appear red.
 
#* False color (RGB=5,4,3 or 4,5,3) tends to distinguish different landcover material.
 
#* False color (RGB=5,4,3 or 4,5,3) tends to distinguish different landcover material.
# In the {{button|text=Layer stack}} pulldown-menu, select {{button|text=Yes}}.
 
# Click the bottom {{button|text=...}} button to select directory and file name to save the result. You can skip this step if you only want to save the result temporarily.
 
# Check the box {{button|text=Open output file after running algorithm}} (if not checked per default) and click {{button|text=Run}}. The resulting map should be added to the [[TOC]] automatically after the algorithm has finished, under the name ''Output layer''.
 
# If necessary, you can rearrange the bands by opening the layer [[Exercise 01: First steps in QGIS|properties]] and selecting the {{button|text=Style}} tab. Adjust the bands as you see fit and confirm with {{button|text=Apply}} or {{button|text=OK}} ('''figure B''').
 
#* For some color composites, (e.g. true color composites), the image may be enhanced by selecting {{button|text=Stretch to MinMax}} from the {{button|text=Contrast enhancement}} menu and selecting the {{button|text=Mean +/- standard deviation x}} radio button. After adjusting the standard deviation factor (a value between 1 and 2 should do), click {{button|text=Load}} and confirm with {{button|text=Apply}} or {{button|text=OK}}.
 
 
[[Image:RemSens_Exercise03_2.png|thumb|center|450px|'''Figure B:''' The ''properties'' dialogue for a multiband raster layer in [[QGIS]] 2.0]]
 
  
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#* For color composites the image may be enhanced by selecting {{button|text=Stretch to MinMax}} from the {{button|text=Contrast enhancement}} menu and selecting the {{button|text=Mean +/- standard deviation x}} radio button. After adjusting the standard deviation factor (a value between 1 and 2), click {{button|text=Load}} and confirm with {{button|text=Apply}} or {{button|text=OK}}.
  
 
==Render Type: Singleband gray==
 
==Render Type: Singleband gray==

Revision as of 21:22, 22 October 2017

The raster layer propertiers differ from the vector layer properties, due to the significant differences of the data. You can open this dialog by double-clicking a raster layer in the TOC or right-clicking on the layer in the TOC and choosing Properties.

Contents

Render Type: Multiband color

    • True color (RGB=3,2,1) simulates the natural color.
    • Standard false color (RGB=4,3,2) makes healthy vegetation generally appear red.
    • False color (RGB=5,4,3 or 4,5,3) tends to distinguish different landcover material.
    • For color composites the image may be enhanced by selecting Stretch to MinMax from the Contrast enhancement menu and selecting the Mean +/- standard deviation x radio button. After adjusting the standard deviation factor (a value between 1 and 2), click Load and confirm with Apply or OK.

Render Type: Singleband gray

A grayscale image is an image with a pixel depth of 8 bit, which means that eight bits are used to represent a single pixel. In QGIS we have the possibility to display raster maps in grayscale via the raster layer properties. See also “Grayscale” on Wikipedia

It makes sense to display a map in greyscale if only one band is available. By default, the scale is calculated by QGIS based on the map itself. Common satellite bands have a data range from 0 to 255.

When displayed in grayscale, 0 is interpreted as black and 255 as white.

In QGIS we can also use the standard deviation of the raster pixels to calculate the scale. In connection with contrast enhancement (the option “Stretch to MinMax” does a good job) this can give a better result, as the scale is not affected by extreme pixel values.



Render Type: Singleband pseudocolor

Pseudocolor is not to be mistaken for false color, the latter one being a composite of three bands. See also: Pseudocolor in Wikipedia

Pseudocolor is a way to display a raster map in which the color scale is derived from a single grayscale band. It can be a good alternative to grayscale if it comes to display metric data like elevation or temperature.

To change map color and symbology, again select the layer in the TOC with a right click and select Properties --> Style. From the pulldown menu Render type, select Singleband pseudocolor. A different menu will come up, where you may select the style of the color map in the section Generate new color map. Click classify and confirm with Apply or OK. The map should now appear in the selected style (figure C).

Figure C: Landsat map displayed in pseudocolor


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