Fenêtre Propriétés de la couche raster

To view and set the properties for a raster layer, double click on the layer name in the map legend, or right click on the layer name and choose Properties from the context menu. This will open the Raster Layer Properties dialog.

Il y a plusieurs onglets dans cette fenêtre :

Astuce

Mise à jour du rendu en direct

Le: ref: layer_styling_panel vous fournit certaines des caractéristiques communes de la boîte de dialogue des propriétés des calques et est un bon widget modélisé que vous pouvez utiliser pour accélérer la configuration des styles de calque et afficher automatiquement vos modifications dans le canevas de la carte.

Note

Because properties (symbology, label, actions, default values, forms…) of embedded layers (see Inclusion de projets) are pulled from the original project file and to avoid changes that may break this behavior, the layer properties dialog is made unavailable for these layers.

Information Properties

The metadata Information tab is read-only and represents an interesting place to quickly grab summarized information and metadata on the current layer. Provided information are:

  • based on the provider of the layer (format of storage, path, data type, extent, width/height, compression, pixel size, statistics on bands, number of columns, rows and no-data values of the raster…);
  • picked from the filled metadata: access, links, contacts, history… as well as data information (CRS, Extent, bands…).

Source Properties

The system Source tab displays basic information about the selected raster, including:

  • the Layer name to display in the Layers Panel;
  • setting the Coordinate Reference System: Displays the layer’s Coordinate Reference System (CRS) as a PROJ.4 string. You can change the layer’s CRS, selecting a recently used one in the drop-down list or clicking on setProjection Select CRS button (see Sélectionneur de système de coordonnées de référence). Use this process only if the CRS applied to the layer is a wrong one or if none was applied. If you wish to reproject your data into another CRS, rather use layer reprojection algorithms from Processing or Save it into another layer.
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Raster Layers - Source Properties Dialog

Symbology Properties

Rendu des bandes raster

QGIS propose quatre Types de rendu. Le choix s’effectue en fonction du type de données.

  1. Multiband color - if the file comes as a multiband with several bands (e.g., used with a satellite image with several bands).
  2. Paletted/Unique values - for single band files that come with an indexed palette (e.g., used with a digital topographic map) or for general use of palettes for rendering raster layers.
  3. Singleband gray - (one band of) the image will be rendered as gray; QGIS will choose this renderer if the file has neither multibands nor an indexed palette nor a continuous palette (e.g., used with a shaded relief map).
  4. Singleband pseudocolor - this renderer is possible for files with a continuous palette, or color map (e.g., used with an elevation map).
  5. Hillshade - Creates hillshade from a band.

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. QGIS automatically fetches Min and Max values for each band of the raster and scales the coloring accordingly. You can control the value ranges with the help of the Min/Max Value Settings section.

A Contrast enhancement method can also be applied to the values: “No enhancement”, “Stretch to MinMax”, “Stretch and clip to MinMax” and “Clip to min max”.

Note

Amélioration de contraste

Lors de l’ajout d’une couche raster GRASS, l’option Amélioration de contraste sera automatiquement Étirer jusqu’au MinMax, quelles que soient les options générales de QGIS définies pour cette option.

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Raster Symbology - Multiband color rendering

Astuce

Visualiser une seule bande d’un raster multibande

If you want to view a single band of a multiband image (for example, Red), you might think you would set the Green and Blue bands to Not Set. But this is not the correct way. To display the Red band, set the image type to Singleband gray, then select Red as the Gray band to use.

Paletted/Unique values

This is the standard render option for singleband files that include a color table, where a certain color is assigned to each pixel value. In that case, the palette is rendered automatically.

It can be used for all kinds of raster bands, assigning a color to each unique raster value.

If you want to change a color, just double-click on the color and the Select color dialog appears.

It is also possible to assign labels to the colors. The label will then appear in the legend of the raster layer.

Right-clicking over selected rows in the color table shows a contextual menu to:

  • Change Color… for the selection
  • Change Opacity… for the selection
  • Change Label… for the selection
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Raster Symbology - Paletted unique value rendering

The pulldown menu, that opens when clicking the (Advanced options) button below the color map to the right, offers color map loading (Load Color Map from File…) and exporting (Export Color Map to File…), and loading of classes (Load Classes from Layer).

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 range of values to color other than the default Min and Max values of the whole raster, thanks to the Min/Max Value Settings option.

Again, a Contrast enhancement method can be applied to the values: “No enhancement”, “Stretch to MinMax”, “Stretch and clip to MinMax” and “Clip to min max”.

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Raster Symbology - Singleband gray rendering

Singleband pseudocolor

This is a render option for single-band files that include a continuous palette. You can also create color maps for a bands of a multiband raster.

../../../_images/rasterSingleBandPseudocolor.png

Raster Symbology - Singleband pseudocolor rendering

Using a Band of the layer and a values range, three types of color Interpolation are available:

  • Discrete (a <= symbol appears in the value column)
  • Linéaire
  • Exact (an equal symbol appears in the Value column)

The Color ramp drop down list lists the color ramp in your QGIS. You can add a new one, edit or save the one you changed. The name of the color ramp will be saved in the configuration and in the QML files.

The Label unit suffix is a label added after the value in the legend.

For the classification Mode selectString “Equal interval”, you only need to select the number of classes selectNumber and press the button Classify. In the case of the Mode selectString “Continuous”, QGIS creates classes automatically depending on the Min and Max.

The button signPlus Add values manually adds a value to the individual color table. The button signMinus Remove selected row deletes a value from the individual color table. 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.

Right-clicking over selected rows in the color table shows a contextual menu to:

  • Change Color… for the selection
  • Change Opacity… for the selection

You can use the buttons fileOpen Load color map from file or fileSaveAs Export color map to file to load an existing color table or to save the color table for later use.

The checkbox Clip out of range values allows QGIS to not render pixel greater than the Max value.

Hillshade

Render a band of the raster layer using hillshading.

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Raster Symbology - Hillshade rendering

Options:

  • Band: The raster band to use.
  • Altitude: The elevation angle of the light source (default is 45°).
  • Azimuth: The azimuth of the light source (default is 315°).
  • Z Factor: Scaling factor for the values of the raster band (default is 1).
  • checkbox Multidirectional: Specify if multidirectional hillshading is to be used (default is off).

Setting the min and max values

By default, QGIS reports the Min and Max values of the band(s) of the raster. A few very low and/or high values can have a negative impact on the rendering of the raster. The Min/Max Value Settings menu helps you control the values to render.

../../../_images/rasterMinMaxValues.png

Raster Symbology - Min and Max Value Settings

Available options are:

  • radioButtonOff User defined: The default Min and Max values of the band(s) can be overridden
  • radioButtonOff Cumulative count cut: Removes outliers. The standard range of values is 2% to 98%, but can be adapted manually.
  • radioButtonOn Min/max: Uses the whole range of values in the image band.
  • radioButtonOff Mean +/- standard deviation x: Creates a color table 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.

Calculations of the min and max values of the bands are made based on the:

  • Statistics extent: it can be Whole raster, Current canvas or Updated canvas. Updated canvas means that min/max values used for the rendering will change with the canvas extent (dynamic stretching).
  • Accuracy, which can be either Estimate (faster) or Actual (slower).

Note

For some settings, you may need to press the Apply button of the layer properties dialog in order to display the actual min and max values in the widgets.

Rendu des couleurs

Pour chaque type de Rendu par bande, des options de Rendu de la couleur sont disponibles.

Vous pouvez réaliser des effets spéciaux sur le rendu de vos rasters en utilisant un des modes de fusion (voir Modes de fusion).

D’autres paramètres permettent de modifier la Luminosité, la Saturation et le Contraste. Vous pouvez également utiliser un Dégradé de gris et le faire “Par clarté”, “Par luminosité”, ou “Par moyenne”. Pour une teinte de couleur, vous pouvez en modifier la “Force”

Ré-échantillonnage

Les options de Ré-échantillonnage déterminent l’apparence d’un raster quand vous zoomez ou dé-zoomez. Différents modes de ré-échantillonnage permettent d’optimiser l’apparence d’un raster. Ils calculent une nouvelle matrice de valeurs via une transformation géométrique.

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Raster Symbology - Color rendering and Resampling settings

En appliquant la méthode “Plus proche voisin”, le raster peut apparaître pixelisé lorsque l’on zoome dessus. Ce rendu peut être amélioré en choisissant les méthodes “Bilinéaire” ou “Cubique” qui adoucissent les angles. L’image est alors lissée. Ces méthodes sont adaptées par exemple aux rasters d’élévation.

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

Propriétés de transparence

transparency QGIS has the ability to display each raster layer at a different transparency level. Use the transparency slider slider to indicate to what extent the underlying layers (if any) should be visible through the current raster layer. This is very useful if you like to overlay more than one raster layer (e.g., a shaded relief map overlayed by a classified raster map). This will make the look of the map more three dimensional.

../../../_images/rasterTransparency.png

Raster Transparency

De plus, vous pouvez entrer une valeur raster qui sera traitée comme NODATA dans l’option Valeur nulle supplémentaire.

An even more flexible way to customize the transparency can be done in the Custom transparency options section:

  • Use Transparency band to apply transparency on an entire band.

  • Provide a list of pixels to make transparent with the corresponding level of transparency:

    1. Cliquez sur le bouton signPlus Ajouter des valeurs manuellement. Une nouvelle ligne apparait dans la liste des pixels.
    2. Enter the Red, Green and Blue values of the pixel and adjust the Percent Transparent to apply.
    3. Alternatively, you can directly fetch the pixel values directly from the raster using the contextHelp Add values from display button. Then enter the transparency value.
    4. Repeat the steps to adjust more values with custom transparency.
    5. Press the Apply button and have a look at the map.

    Comme vous pouvez le voir, il est assez facile de définir une transparence personnalisée, mais cela peut prendre un peu de temps. Par conséquent, vous pouvez utiliser le bouton fileSave Exporter dans un fichier pour sauver vos paramètres de transparence dans un fichier. Le bouton fileOpen Importer depuis le fichier charge vos paramètres de transparence et les applique à la couche raster actuelle.

Propriétés de l’Histogramme

The rasterHistogram Histogram tab allows you to view the distribution of the bands or colors in your raster. The histogram is generated when you press the Compute Histogram button. All existing bands will be displayed together. You can save the histogram as an image with the fileSave button.

At the bottom of the histogram, you can select a raster band in the drop-down menu and Set min/max style for it. The actionRun Prefs/Actions drop-down menu gives you advanced options to customize the histogram:

  • With the Visibility option, you can display histograms of the individual bands. You will need to select the option radioButtonOff Show selected band.
  • The Min/max options allow you to “Always show min/max markers”, to “Zoom to min/max” and to “Update style to min/max”.
  • The Actions option allows you to “Reset” or “Recompute histogram” after you changed the min or max values of the band(s).
../../../_images/rasterHistogram1.png

Histogramme raster

Rendering Properties

In the rendering Rendering tab, it’s possible to:

  • apply a Scale dependent visibility to the layer: You can set the Maximum (inclusive) and Minimum (exclusive) scale, defining a range of scale in which the layer will be visible. Out of this range, it’s hidden. The mapIdentification Set to current canvas scale button helps you use the current map canvas scale as boundary of the range visibility. See Rendu dépendant de l’échelle for more information.
  • Refresh layer at interval (seconds): set a timer to automatically refresh individual layers at a matching interval. Canvas updates are deferred in order to avoid refreshing multiple times if more than one layer has an auto update interval set.

Vous pouvez définir une échelle Maximum (inclusive) et Minimum (exclusive), correspondant à une plage d’échelles pour lesquelles les couches sont visibles. En dehors de cette plage, elles sont cachées. Le bouton mapIdentification Mettre à l’échelle actuelle du canevas permet d’utiliser l’échelle actuelle pour l’une ou l’autre des limites de la plage de visibilité. Voir Rendu dépendant de l’échelle pour plus d’informations.

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Raster Rendering

Propriétés des Pyramides

Les couches raster à haute résolution peuvent ralentir la navigation dans QGIS. En créant des copies des données de plus basses résolutions (des pyramides), les performances peuvent être considérablement améliorées puisque QGIS sélectionne la résolution la plus pertinente à utiliser en fonction du niveau de zoom.

Vous devez avoir accès en écriture dans le répertoire où les données originelles sont stockées pour construire les pyramides.

From the Resolutions list, select resolutions for which you want to create pyramid by clicking on them.

If you choose Internal (if possible) from the Overview format drop-down menu, QGIS tries to build pyramids internally.

Note

Notez que construire des pyramides peut altérer le fichier original et, une fois créées, elles ne peuvent plus être supprimées. Si vous désirez préserver une version “sans pyramide” de vos raster, réalisez une copie de sauvegarde avant de les construire.

If you choose External and External (Erdas Imagine) the pyramids will be created in a file next to the original raster with the same name and a .ovr extension.

Several Resampling methods can be used to calculate the pyramids:

  • Plus proche voisin
  • Moyenne
  • Gauss
  • Cubique
  • Cubic Spline
  • Laczos
  • Mode
  • Aucune

Finally, click Build Pyramids to start the process.

../../../_images/rasterPyramids.png

Pyramides Raster

Propriétés des Métadonnées

The editMetadata Metadata tab provides you with options to create and edit a metadata report on your layer. See vector layer metadata properties for more information.

Propriétés de la Légende

The legend Legend tab provides you with a list of widgets you can embed within the layer tree in the Layers panel. The idea is to have a way to quickly access some actions that are often used with the layer (setup transparency, filtering, selection, style or other stuff…).

By default, QGIS provides transparency widget but this can be extended by plugins registering their own widgets and assign custom actions to layers they manage.

QGIS Server Properties

The overlay QGIS Server tab displays a wealth of information about the raster layer, including statistics about each band in the current raster layer. From this tab, entries may be made for the Description, Attribution, MetadataUrl and Properties. In Properties, statistics are gathered on a “need to know” basis, so it may well be that a given layer’s statistics have not yet been collected.

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QGIS Server in Raster Properties