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Dialogul Proprietăților Rasterului

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 (see figure_raster_properties).

There are several tabs in the dialog:

  • General
  • Style
  • Transparency
  • Pyramids
  • Histogram
  • Metadata
  • Legend
../../../_images/rasterPropertiesDialog.png

Raster Layers Properties Dialog

Tip

Live update rendering

The Layer Styling Panel provides you with some of the common features of the Layer properties dialog and is a good modeless widget that you can use to speed up the configuration of the layer styles and automatically view your changes in the map canvas.

Note

Because properties (symbology, label, actions, default values, forms...) of embedded layers (see Imbricarea Proiectelor) 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.

General Properties

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 setProjection Select CRS button (see Coordinate Reference System Selector). 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.

Scale dependent visibility

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 Randarea Dependentă de Scară for more information.

Style Properties

Randare bandă

QGIS oferă patru Tipuri de Render diferite. Renderul ales depinde de tipul datelor.

  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’.

../../../_images/rasterMultibandColor.png

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 radioButtonOn Estimate (faster) the Min and Max values of the bands or use the radioButtonOff 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 radioButtonOn 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 radioButtonOff 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 radioButtonOff Mean +/- standard deviation x selectNumber. 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 radioButtonOff Current extent.

Tip

Vizualizarea unei singure benzi dintr-un Raster Multibandă

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 band to use for Gray.

Paletted

Aceasta este opțiunea de randare standard pentru fișierele simplă bandă care includ deja un tabel de culori, în care valoarea fiecărui pixel este atribuită unei anumite culori de randare. În acest caz, paleta este randată automat. Dacă doriți să modificați culorile atribuite anumitor valori, doar faceți dublu-clic pe culoare și pe dialogul de Selectare culoare care apare. De asemenea, în QGIS este posibilă asignarea unei etichete valorilor culorilor. În acel caz, eticheta va apărea în legenda stratului raster.

../../../_images/rasterPaletted.png

Raster Style - Paletted Rendering

Îmbunătăţirea contrastului

Note

Atunci când se adaugă rastere GRASS, opțiunea de Îmbunătățire a contrastului va fi întotdeauna setată automat pe întindere la min max, indiferent dacă aceasta este setată la o altă valoare în opțiunile generale ale QGIS.

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 radioButtonOn Estimate (faster) the Min and Max values of the bands or use the radioButtonOff Actual (slower) Accuracy.

../../../_images/rasterSingleBandGray.png

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 radioButtonOn 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 radioButtonOff Min/max and radioButtonOff Mean +/- standard deviation x selectNumber. 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

Aceasta este o opțiune de randare pentru fișierele simplă bandă, incluzând o paletă continuă. Puteți crea aici, de asemenea, hărți individuale de culoare pentru benzile unice.

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

Raster Style - Singleband pseudocolor rendering

Three types of color interpolation are available:

  1. Discrete
  2. Liniar

  3. Exact

In the left block, 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, and the arrowDown 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 draw Load color map from band, which tries to load the table from the band (if it has any). And 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 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 selectString ‘Equal interval’, you only need to select the number of classes selectNumber and press the button Classify. You can invert the colors of the color map by clicking the checkbox Invert checkbox. In the case of the Mode selectString ‘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 radioButtonOn 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 radioButtonOff 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 radioButtonOff Mean +/- standard deviation x selectNumber. Then, only the values within the standard deviation or within multiple standard deviations are considered for the color table.

Randarea culorii

Pentru fiecare Randare de bandă, este posibilă o Randare de culoare.

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

Mai multe setări pot fi făcute prin modificarea Strălucirii, a Saturației și a Contrastului. Puteți utiliza, de asemenea, o opțiune Grayscale, în care puteți alege între ‘By lightness’, ‘By luminosity’ și ‘By average’. Pentru o nuanță din tabelul de culori, puteți modifica ‘Strength’.

Reeşantionare

Opțiunea Reeșantionare își face apariția atunci când măriți și micșorați o imagine. Modurile de reeșantionare pot optimiza aspectul hărții. Eie calculează o nouă matrice cu valori de gri, printr-o transformare geometrică.

../../../_images/rasterRenderAndRessampling.png

Raster Style - Color rendering and Resampling settings

Atunci când se aplică metoda ‘Celui mai apropiat vecin ‘, harta poate avea o structură pixelată, la efectuarea unei transfocări. Aceasta aspect poate fi îmbunătățit prin utilizarea metodei ‘Biliniară’ sau ‘Cubică’, care poate determina ca entitățile ascuțite să fie neclare. Efectul constă într-o imagine mai fină. Această metodă poate fi aplicată, de exemplu, pentru hărți raster, topografice, digitale.

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

Transparency Properties

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 though 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.

Additionally, you can enter a raster value that should be treated as NODATA in the Additional no data value option.

An even more flexible way to customize the transparency can be done in the Custom transparency options section. The transparency of every pixel can be set here.

As an example, we want to set the water of our example raster file landcover.tif to a transparency of 20%. The following steps are necessary:

  1. Load the raster file landcover.tif.
  2. Open the Properties dialog by double-clicking on the raster name in the legend, or by right-clicking and choosing Properties from the pop-up menu.
  3. Select the Transparency tab.
  4. From the Transparency band drop-down menu, choose ‘None’.
  5. Clic pe butonul signPlus Add values manually. Un nou rând va apărea în lista pixelilor.

  6. Enter the raster value in the ‘From’ and ‘To’ column (we use 0 here), and adjust the transparency to 20%.
  7. Press the [Apply] button and have a look at the map.

You can repeat steps 5 and 6 to adjust more values with custom transparency.

După cum se poate vedea, deși este destul de ușor de stabilit transparența după dorință, trebuie parcurși o mulțime de pași. Prin urmare, puteți utiliza butonul fileSave Export în fișier pentru a salva setările de transparență într-un fișier. Butonul de fileOpen Import din fișier încarcă setările de transparență și le aplică stratului raster curent.

Proprietățile Piramidelor

Straturile raster cu rezoluție mare pot încetini navigarea în QGIS. Prin crearea unor copii de rezoluție scăzută a datelor (piramide), performanța poate crește considerabil, întrucât QGIS utilizează cea mai potrivită rezoluție, în funcție de nivelul de transfocare.

Trebuie să aveți acces de scriere în directorul în care sunt stocate datele originale, pentru a construi piramide.

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

Rețineți că realizarea piramidelor interne poate modifica fișierul de date original, iar o dată create ele nu mai pot fi eliminate! Dacă doriți să păstrați o versiune ‘fără-piramide’ a rasterului dvs., faceți o copie de rezervă înainte de construirea piramidelor.

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:

  • cel mai apropiat vecin

  • Medie

  • Gauss
  • Cubic
  • Mod

  • Niciuna

Finally, click [Build pyramids] to start the process.

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

Raster Pyramids

Histogram Properties

The Histogram tab allows you to view the distribution of the bands or colors in your raster. The histogram is generated automatically when you open the Histogram tab. All existing bands will be displayed together. You can save the histogram as an image with the fileSave button. With the Visibility option in the actionRun Prefs/Actions menu, 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’. With the Actions option, you can ‘Reset’ and ‘Recompute histogram’ after you have chosen the Min/max options.

../../../_images/rasterHistogram.png

Histograma Raster

Metadata Properties

The Metadata 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.

../../../_images/rasterMetadata.png

Raster Metadata

Legend Properties

The 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.