Proprietà raster¶

Layer Info¶

The General tab 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¶

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 ^{Select CRS} button (see Scelta del sistema di riferimento delle coordinate). 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.

Visualizzazione banda¶

QGIS offre quattro Tipo visualizzazione. La scelta dipende dal tipo di dato.

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 - 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 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)

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’.

Raster Style - Multiband color rendering

This selection offers you a wide range of options to modify the appearance of your raster layer. 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 a 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% to 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 all of the data included in the original image (e.g., QGIS creates a color table with 256 values, given the fact that you have 8 bit 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 calculations can also be made for the Current extent.

Paletted

Questa è l’opzione normale di visualizzazione per i file a banda singola che includono già una tabella di colori, dove ad ogni valore di pixel viene assegnato un determinato colore. In questo caso, la tavolozza viene visualizzata automaticamente. Se vuoi modificare i colori assegnati a determinati valori, basta fare doppio click sul colore e viene visualizzata la finestra di dialogo Scegli colore. Inoltre, in QGIS puoi assegnare un’etichetta ai valori di colore. L’etichetta compare quindi nella legenda del layer raster.

Raster Style - Paletted Rendering

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 by choosing the Extent first and then pressing [Load]. QGIS can Estimate (faster) the Min and Max values of the bands or use the Actual (slower) Accuracy.

Raster Style - Singleband gray rendering

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% to 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 all of the data included in the original image, the second 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.

Singleband pseudocolor

Questa è l’opzione di visualizzazione per i file a banda singola che includono una tavolozza continua. Qui puoi anche creare mappe di colori specifici per le bande singole.

Raster Style - Singleband pseudocolor rendering

Three types of color interpolation are available:

1. Discrete

2. Lineare

3. Exact

In the left block, the button ^{Add values manually} adds a value to the individual color table. The 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 color maps. 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 color map by clicking the Invert checkbox. In the case of the Mode ‘Continuous’, QGIS creates classes automatically depending on the Min and Max. Defining Min/Max values can be done with the help of the Load min/max values section. A lot of images have a 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% to 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 all of the data included in the original image (e.g., QGIS creates a color table with 256 values, given the fact that you have 8 bit 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.

Visualizzazione colore¶

Per ogni Visualizzazione banda, è disponibile una Visualizzazione colore.

Puoi anche ottenere effetti speciali per i tuoi file(s) raster usando una delle modalità di fusione (vedi Metodi di fusione).

Ulteriori impostazioni possono essere fatte modificando la Luminosità, la Saturazione e il Contrasto. Puoi usare anche l’opzione Scala di grigi dove puoi scegliere fra ‘Per chiarezza’, ‘Per luminosità’ e ‘Per media’. Puoi modificare la ‘Forza’ per ogni tonalità della tabella dei colori.

Ricampionamento¶

La sezione Ricampionamento ha effetto quando ingrandisci o rimpicciolisci l’immagine. I metodi di ricampionamento ottimizzano l’aspetto della mappa perché calcolano una nuova matrice di grigi attraverso una trasformazione geometrica.

Raster Style - Color rendering and Resampling settings

Applicando il metodo ‘vicino più prossimo’ la mappa potrebbe avere una struttura con molti pixel quando viene ingrandita. Questo aspetto può essere migliorato usando i metodi ‘Bilineare’ o ‘Cubico’ perché creano delle geometrie più appuntite e offuscate. Il risultato è un’immagine più morbida. Puoi applicare questo metodo, per esempio, a mappe raster topografiche.

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