Raster layers generally refer to images, including multispectral, panchromatic, digital elevation models (DEMs), and masks. For information about classification images, see Class Layers.
See the following sections:
Manage Raster Layers
The Layer Manager lists all displayed files in a tree view. Raster layers that are open but are not displayed in an Image window view are listed only in the Data Manager.
Each time you open a new data file, the layer appears at the top of the Layer Manager and becomes the selected layer. The purpose of a selected layer is to allow you to apply a display enhancement (brightness, contrast, transparency, etc.) to that layer only, without affecting other layers.
Here are some general tips for working with raster layers:
- To select a layer, click its name in the Layer Manager.
- To select multiple layers to remove or create a Quick Mosaic, use the Ctrl or Shift key and select the relevant layers. Then right-click and select Remove or Quick Mosaic.
- To unselect multiple layers that were selected, click the View layer at the top of the Layer Manager.
- Basic metadata (such as name, dimensions, sensor, etc.) of a raster layer is displayed beneath the Toolbox in the lower-right corner of the ENVI application.
- To hide a layer in a view, disable the check box for that layer in the Layer Manager. To show the layer, enable the check box.
- To hide all layers in a view, right-click on the View icon in the Layer Manager and select Hide All Layers. To show all layers, right-click and select Show All Layers.
- If a raster has bad bands defined in the header file, those bands are marked with a warning symbol in the Layer Manager.
- If you created multiple views in the Image window, the layers for each view are grouped under View entries.
- To create a new RGB layer consisting of three bands from different files, follow these steps. The images must be coregistered and have the same x and y dimensions. Bands from a palette-based image are not supported.
- Open the image files in ENVI.
- Start the Data Manager.
- Expand the Band Selection category.
- With the red band selected in the Band Selection category, click on a band name from any file to assign that band to red.
- Repeat for the green and blue bands.
- Click Load Data in the Data Manager.
The resulting RGB image is only added to the Layer Manager for display, not to the Data Manager. To create an RGB layer that you can export to a file, use the Build Layer Stack tool or the ENVIMetaspectralRaster routine in the API.
- If you have multiple views displayed, you can drag-and-drop raster layers from the Layer Manager to any one of those views in the display or to the corresponding view icons in the Layer Manager. This creates a copy of the layer(s) to populate the views.
- Drag-and-drop individual ROI layers or ROI containers from one raster to another, to load the selected ROIs in the new raster layer.
- To add a raster layer to a new view, right-click on a filename in the Data Manager and select Open Selected Dataset in New View.
Manage Individual Layers
For additional options with individual layers, right-click on a raster in the Layer Manager and select an option:
- Rename Item: Enter the new name in the Rename Item dialog and press the Enter key to accept it or press the Esc key to cancel. (Linux and Mac users should click the green check icon to accept the new name or click the red X icon to cancel.)
- Export Layer to TIFF: Save the full raster layer extent, with image enhancements, at full resolution to a TIFF file.
- Display in Portal: Display the raster layer in a portal.
- Change RGB Bands: Change the RGB combination displayed for a multispectral raster. To assign a RGB combination, click the band name to assign to red in the Change Bands dialog, then repeat to make the green and blue selections. Click OK.
- Order: Change the order in which a layer is displayed relative to other layers. Choose one of the following options:
- Bring to Front
- Bring Forward
- Send Backward
- Send to Back
Or, select a layer and drag it to the desired order in the Layer Manager.
Remove: Remove the layer from the Layer Manager. The file remains open and you can access it and redisplay it from the Data Manager.
- New Region of Interest: Create a new ROI layer for the selected raster.
- New Raster Color Slice: Create a new color slice layer for the selected raster.
- New Contour Layer: Create a new contour line layer for the selected raster.
- Band Animation: Animate through the bands of a raster.
- Change Color Table: Change the color table for a grayscale raster. This menu option is not available for single-band layers that contain predefined color palettes, such as ENVI classification images. Choose one of the following predefined color tables:
- Red Temperature
Or, select More to use the ENVI Color Table dialog to create your own color table.
- Profiles: Create plots of spectral, horizontal, vertical, arbitrary, and series profiles.
- View Metadata: Open the Metadata Viewer for a raster layer. Basic metadata properties are also displayed in the lower-right corner of the ENVI application without requiring you to select this menu option.
- Quick Stats: Compute basic statistics and histograms for all bands.
- Zoom to Layer Extent: Center and display the entire layer within a view.
- Zoom to Layer Full Resolution: Zoom to 1:1 (100%) scale.
Note: Selecting Full Extent from the Zoom drop-down menu or clicking the Zoom to Full Extent button in the main toolbar zooms to the combined extents of all layers for the current view. Also, if a raster layer is georeferenced, the Zoom To drop-down list in the main toolbar displays options for Use Map Scale and Use Pixel Scale. For pixel-based raster layers (with no georeferencing), the Zoom To drop-down list only displays options for Use Pixel Scale.
- If you open an OGC WMS raster layer that contains a legend, the legend displays in the Layer Manager. To create an annotation object from the legend that you can overlay on the image, right-click the layer name and select Load Layer as Annotation. This is useful, for example, in creating a Powerpoint presentation from the view.
- Load Current Raster: Load the current raster in a series as a separate layer. This option is only available for raster series data.
Change a Color Table
You can apply a color table to a grayscale image when you right-click the layer in the Layer Manager and select Change Color Table. You can choose from several pre-define color tables, or click More to open the Change Color Table dialog. In the dialog you can pick from more pre-defined IDL color tables, and you can work in RGB (red-green-blue), HLS (hue-lightness-saturation), HSV (hue-saturation-value), or CMY (cyan, magenta, yellow) color spaces to define your own color table.
- When you open the dialog, the Selected Color Table color bar shows the current color table for the image. When you modify the color table, the color bar updates to show the changes and the colors are applied to the image for preview. To accept the new color table and close the dialog, click OK.
- Click Reverse to reverse the order of the color gradient.
- To define your own color table, select RGB, HLS, HSV, or CMY from the drop-down.
- Enable the check box next to the slider bar of the color space element you want to change. The two remaining sliders represent horizontal and vertical axes of the currently displayed color space and remain constant; only the slider with the enabled check box can change the current color space.
- Move the slider bars for an element to adjust the values of the color space.
- In the color space window, click and drag the end points of the interpolation line to change the current color table. The color table will contain the colors that fall beneath this line.
You can change the interpolation method to use on a raster layer or raster series layers. Interpolation behavior may vary, depending on the method you choose, and whether the Use Graphics Card to Accelerate Enhancement Tools preference is enabled. Variations are noted in the following descriptions. The choices are as follows:
- Nearest Neighbor: Each pixel in the displayed image receives its value from the nearest pixel in the input (reference) image. If the Use Graphics Card to Accelerate Enhancement Tools preference is enabled, brightness, contrast, and sharpen filters are performed by the GPU.
- Bilinear: Each estimated pixel value in the displayed image is based on a weighted average of the four nearest neighboring pixels in the input image.
Not all GPUs support bilinear interpolation of floating point textures; therefore, if Use Graphics Card to Accelerate Enhancement Tools is enabled, the setting is ignored and brightness, contrast, and sharpen filters are performed by the CPU.
- Bicubic: Each estimated pixel value in the displayed image is based on a weighted average of the sixteen nearest pixels in the input image. If Use Graphics Card to Accelerate Enhancement Tools is enabled, the setting is ignored and brightness, contrast, and sharpen filters are performed by the CPU. If your graphics processing unit (GPU) does not support OpenGL Shader Language (GLSL), the Nearest Neighbor interpolation method is used instead.
- Optimized Bicubic: (default) Each estimated pixel value in the displayed image is based on a weighted average of the sixteen nearest pixels in the input image. The weighting coefficients are improved over standard Bicubic. If Use Graphics Card to Accelerate Enhancement Tools is enabled, the setting is ignored and brightness, contrast, and sharpen filters are performed by the CPU. If your graphics processing unit (GPU) does not support OpenGL Shader Language (GLSL), the Nearest Neighbor interpolation method is used instead.
To use Bicubic and Optimized Bicubic:
- Your graphics card must support OpenGL 2.0 or higher, and you must have the most recent drivers installed.
- ROIs will always display as Nearest Neighbor, regardless of the preference setting.
Portals behave differently; they try to match the interpolation value of the target layer, regardless of the current preference setting.