Proprietà raster¶

Layer Info¶

The General menu displays basic information about the selected raster, including the layer source path, the display name in the legend (which can be modified) and the number of columns, rows and No-Data Values of the raster.

Coordinate reference system¶

Below you find the coordinate reference system (CRS) information printed as a PROJ.4-string. If this setting is not correct, it can be modified by clicking the [Specify] button.

Scale Dependent visibility¶

Additionally Scale Dependent visibility can be set in this tab. You need to check the checkbox and set an appropriate scale where your data will be displayed in the map canvas.

At the bottom you can see a thumbnail of the layer, its legend symbol, and the palette.

Band rendering¶

QGIS offers four different Render types. The renderer chosen is dependent on the data type.

1. Multiband color - if the file comes as a multi band with several bands (e.g. used with a satellite image with several bands)
2. Paletted - if a single band file comes with an indexed palette (e.g. used with a digital topographic map)
3. Singleband gray- (one band of) the image will be rendered as gray, QGIS will choose this renderer if the file neither has multi bands, nor has an indexed palette nor has a continous palette (e.g. used with a shaded relief map)
4. Singleband pseudocolor - this renderer is possible for files with a continuous palette, e.g. the file has got a color map (e.g. used with an elevation map)

Multiband color

With the multiband color renderer three selected bands from the image will be rendered, each band representing the red, green or blue component that will be used to create a color image. You can choose several Contrast enhancement methods: ‘No enhancement’, ‘Stretch to MinMax’, ‘Stretch and clip to MinMax’ and ‘Clip to min max’.

Figure Raster 2:

Raster Renderer - Multiband color

This selection offers you a wide range of options to modify the appearance of your rasterlayer. First of all you have to get the data range from your image. This can be done by choosing the Extent and pressing [Load]. QGIS can Estimate (faster) the Min and Max values of the bands or use the Actual (slower) Accuracy.

Now you can scale the colors with the help of the Load min/max values section. A lot of images have few very low and high data. These outliers can be eliminated using the Cumulative count cut setting. The standard data range is set from 2% until 98% of the data values and can be adapted manually. With this setting the gray character of the image can disappear. With the scaling option Min/max QGIS creates a color table with the whole data included in the original image. E.g. QGIS creates a color table with 256 values, given the fact that you have 8bit bands. You can also calculate your color table using the Mean +/- standard deviation x . Then only the values within the standard deviation or within multiple standard deviations are considered for the color table. This is useful when you have one or two cells with abnormally high values in a raster grid that are having a negative impact on the rendering of the raster.

All calculation can also be made for the Current extend.

Paletted

This is the standard render option for singleband files that already include a color table, where each pixel value is assigned to a certain color. In that case, the palette is rendered automatically. If you want to change colors assigned to certain values, just double-click on the color and the Select color dialog appears.

Figure Raster 3:

Raster Renderer - Paletted

Miglioramento contrasto

Singleband gray

This renderer allows you to render a single band layer with a Color gradient ‘Black to white’ or ‘White to black’. You can define a Min and a Max value with choosing the Extend first and then pressing [Load]. QGIS can Estimate (faster) the Min and Max values of the bands or use the Actual (slower) Accuracy.

Figure Raster 4:

Raster Renderer - Singleband gray

With the Load min/max values section scaling of the color table is possible. Outliers can be eliminated using the Cumulative count cut setting. The standard data range is set from 2% until 98% of the data values and can be adapted manually. With this setting the gray character of the image can disappear. Further settings can be made with Min/max and Mean +/- standard deviation x . While the first one creates a color table with the whole data included in the original image the second creates a colortable that only considers values within the standard deviation or within multiple standard deviations. This is useful when you have one or two cells with abnormally high values in a raster grid that are having a negative impact on the rendering of the raster.

Singleband pseudocolor

This is a render option for single band files including a continous palette. You can also create individual color maps for the single bands here.

Figure Raster 5:

Raster Renderer - Singleband pseudocolor

Three types of color interpolation are available:

1. Discrete

2. Lineare

3. Esatto

In the left block the button ^{Add values manually} adds a value to the individual color table. Button ^{Remove selected row} deletes a value from the individual color table and the ^{Sort colormap items} button sorts the color table according to the pixel values in the value column. Double clicking on the value-column lets you insert a specific value. Double clicking on the color-column opens the dialog Change color where you can select a color to apply on that value. Further you can also add labels for each color but this value won’t be displayed when you use the identify feature tool. You can also click on the button ^{Load color map from band}, which tries to load the table from the band (if it has any). And you can use the buttons ^{Load color map from file} or ^{Export color map to file} to load an existing color table or to save the defined color table for other sessions.

In the right block Generate new color map allows you to create newly categorized colormaps. For the Classification mode ‘Equal interval’ you only need to select the number of classes and press the button Classify. You can invert the colors of the the color map by clicking the Invert checkbox. In case of the Mode ‘Continous’ QGIS creates classes depending on the Min and Max automatically. Defining Min/Max values can be done with the help of Load min/max values section. A lot of images have few very low and high data. These outliers can be eliminated using the Cumulative count cut setting. The standard data range is set from 2% until 98% of the data values and can be adapted manually. With this setting the gray character of the image can disappear. With the scaling option Min/max QGIS creates a color table with the whole data included in the original image. E.g. QGIS creates a color table with 256 values, given the fact that you have 8bit bands. You can also calculate your color table using the Mean +/- standard deviation x . Then only the values within the standard deviation or within multiple standard deviations are considered for the color table.

Color rendering¶

For every Band rendering a Color rendering is possible.

You can achieve special rendering effects for your raster file(s) using one one of the blending modes (see blend_modes).

Further settings can be made in modifiying the Brightness, the Saturation and the Contrast. You can use a Grayscale option where you can choose between ‘By lightness’, ‘By luminosity’ and ‘By average’. For one hue in the color table you can modiy the ‘Strength’.

Resampling¶

The Resampling option makes it appearance when you zoom in and out of the image. Resampling modes can optimize the appearance of the map. They calculate a new gray value matrix through a geometric transformation.

While applying the ‘Nearest neighbour’ method the map can have a pixelated structure when zooming in. This appearance can be improved by using the ‘Bilinear’ or ‘Cubic’ method. Sharp features are caused to be blurred now. The effect is a smoother image. The method can be applied e.g. to digital topographic raster maps.