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ENVI

Manage Raster Data

Manage Raster Data

See the following sections:

Convert Complex Data


Use Convert Complex Data to output selected images calculated from complex data. Image types included are: Real (real portion of number), Imaginary (imaginary portion), Power (natural log of magnitude), Magnitude (square root of sum of the squares of the real and imaginary), and Phase (arc tangent of imaginary divided by real).

  1. From the Toolbox, select Raster Management > Convert Complex Data.
  2. Select an input data file.
  3. Click OK. The Convert Complex Parameters dialog appears. Select the output band functions by selecting the check boxes next to the function names.
  4. Select output to File or Memory.
  5. Click OK. ENVI adds the resulting output to the Layer Manager.

Convert Interleave


Use Convert Interleave to convert between common data storage conventions. Often, it is more efficient to use image data stored in a specific manner for specific processing operations or interactive analysis.

  1. From the Toolbox, select Raster Management > Convert Interleave.
  2. Select an input file and perform optional spatial and spectral subsetting, then click OK. The Convert File Parameters dialog appears.
  3. Choose the output data type from the Output Interleave radio buttons. ENVI automatically determines the format of the input file and offers conversion to the other two formats.
  4. From the Convert in Place toggle button, select Yes or No.
    • Yes: Overwrites the existing file. This option saves significant disk space, but the process is slower than writing to a separate file.
    • No: Writes the converted file to a separate output file.

      Note: If the overwrite function fails for any reason (for example, due to a power outage), your data will be corrupted and the original file will not be recoverable.

  5. Enter the output filename.
  6. Click OK. ENVI adds the resulting output to the Layer Manager.

Create Coordinate System String


Use Create Coordinate System String to create a text file containing a coordinate system string that you can add to an ENVI header file (.hdr) or use with the ENVI application programming interface (API).

  1. From the Toolbox, select Raster Management > Create Coordinate System String.
  2. Select a coordinate system. Click to expand the lists of Geographic Coordinate Systems or Projected Coordinate Systems, then select the specific coordinate system. Its properties display in the Selected Coordinate System table. The steps for using this dialog are similar to those of the Select Coordinate System dialog. Refer to those steps for defining and editing coordinate systems, and for adding commonly used coordinate systems to a list of favorites.

  3. Click OK in the Create Coordinate System dialog.
  4. A dialog appears, prompting you for a text filename and location. Select a folder and filename to save the text file, then click Save. The default filename is coordSysString.txt, but you can change it to be more descriptive for each coordinate system string that you save.

Create ENVI Meta File


A meta file is a text file that contains the names of image files and/or bands to treat as one virtual file. When you later select the meta file for input or processing using File > Open, ENVI retrieves the image data from the individual disk files and treats them as if they were part of the same input file for processing.

  • ENVI meta files can contain images with different data types (byte, integer, floating point, and so forth), which allows you to combine processing of diverse data sets. ENVI does not need to perform file conversions or create intermediate processing files.
  • The files that comprise the meta file must have the same spatial dimensions. You can spatially subset the files if needed; see Step 3 below.
  • The map projection of the first file or band in the meta file determines the projection for the other files/bands. The other files/bands are not reprojected to match the projection of the first file/band. You can also create an ENVI header file to accompany the meta file that defines the map projection.
  • You can include any file type in a meta file as long as the files reside on disk and they are formats that ENVI supports.

Follow these steps to continue:

  1. From the Toolbox, select Raster Management > Create ENVI Meta File. The ENVI Meta File Builder dialog appears.
  2. Click the Add Dataset button and select a file using the File Selection dialog.
  3. Repeat the file selection process using the Add Dataset button. Input files are listed in the Selected Datasets for ENVI Meta File list.
    • To delete a file from the list in the New File Builder dialog, select the filename and click the Remove button.
    • To change the order in which the files and/or bands are imported, click the Move Up or Move Down buttons.
  4. In the Output Filename field, enter a filename and location.
  5. Select the Display Output option to automatically display the image files and/or bands once the meta file has been created.
  6. Click OK to build the new file.
  7. Optional: You can use the Edit ENVI Header tool create an accompanying header file.

Data Viewer


Use the Data Viewer to examine data files at the byte level, which allows you to view file structure, identify unknown file types, and determine the offset to data when an embedded image header is present in the data.

  1. From the Toolbox, select Raster Management > Data Viewer.
  2. Select an input file. The Data Viewer dialog appears, displaying the filename and number of total bytes in the title bar and the actual data values (in hexadecimal format, by default).
    • The first column lists the byte count (the starting byte of the listed row).
    • The next 16 columns (for hexadecimal and byte data) list the values for 16 bytes of data.
    • The final column lists the ASCII equivalent of the values.

    Note: If the data does not have any embedded ASCII characters, the ASCII equivalents are random. If there is embedded ASCII data, the data is readable as text.

  3. To select the starting byte to view from the file, enter the byte number in the File Offset Byte(s) field.
  4. To move the data view forward or backward one page respectively, click the Next Page and Prev Page buttons.
  5. If you suspect that the data may be in something other than byte format, select View_Format from the Data Viewer menu bar and select a data format (Hexadecimal, Byte, Unsigned Integer, Integer, Long Integer, Unsigned Long Integer, or Floating Point). The number of columns of data values and the representation of the listed data change accordingly.
  6. To open and view a different file, select File > Open New File from the Data Viewer menu bar.
  7. To exit the data viewer, select File > Cancel from the Data Viewer menu bar.
  8. To evaluate the swapping of bytes between Intel and IEEE formats for data types with more than one byte per value (integer, long integer, and floating point), select Byte_Swap from the Data Viewer menu bar and select one of the following:
    • None: No swapping
    • Short Word: Swapping two bytes for an integer
    • Long Word: Swapping byte pairs for long integer and floating-point data

Destripe


Use Destripe data to remove periodic scan line striping in image data. This type of striping is often seen in Landsat MSS data (every 6th line) and less commonly, in Landsat TM data (every 16th line). When destriping the data, ENVI calculates the mean of every nth line and normalizes each line to its respective mean. In order for destriping to function properly, the data must be in the acquired format (horizontal strips) and cannot be rotated or georeferenced.

  1. From the Toolbox, select Raster Management > Destripe.
  2. Select an input file and perform optional spatial and spectral subsetting, then click OK. The Destriping Parameters dialog appears.
  3. Enter the number of detectors in the Number of Detectors field. The number of detectors is the periodicity of the striping (for example, for Landsat MSS, the value would be 6). If the file type has been set in the header, the default is set automatically.
  4. Select output to File or Memory.
  5. Click OK.

Generate Test Data


Use Generate Test Data to create a variety of test images that may be useful for demonstrating or testing ENVI features. These include constant value images, horizontal and vertical ramps, random number images using both uniform and normal distributions, and images generated using a Gaussian Point Spread function.

  1. From the Toolbox, select Raster Management > Generate Test Data. The Generate Image Parameters dialog appears.
  2. Select the output image type from the Output Image Value drop-down list:
    • Constant: Generates an image with a constant value for every pixel. Enter the desired DN value in the Value text box.
    • Horiz Ramp or Vert Ramp: Generates an image with either a horizontal or vertical linear ramp. Enter the desired minimum and maximum ramp values in the Min Value and Max Value fields.
    • Random (uniform) or Random (normal): Random (normal) returns an image with normally-distributed random numbers. Random (uniform) returns an image with uniformly-distributed random numbers. Enter the minimum and maximum values to occur in the image in Min Value and Max Value fields. Enter a Seed value to initialize the random number generator. If you do not enter a seed value, ENVI uses the system clock for initialization.
    • Gaussian PSF: Generates a Gaussian image. Enter the minimum and maximum values to occur in the number of output Samples, Lines, and Bands in the corresponding fields.
  3. Select the Output Data Type from the drop-down list.
  4. Select output to File or Memory.
  5. Click OK. A status box appears while the image is being processed. ENVI adds the new image to the Layer Manager when processing is complete.

Import IDL Variables


Use Import IDL Variables to import IDL variables into ENVI.

  1. From the Toolbox, select Raster Management > Import IDL Variables. The Import IDL Variables dialog appears with a list of all defined variables.
  2. Select the desired variable names to import by clicking in the check box next to the name.
    • To add a range of variable names, enter the starting and ending variable numbers and click Add Range.
    • To select all the variable names, click Select All.
    • To clear the selected variable names, click Clear.
  3. To save a copy of the data in IDL, use the arrow toggle button to select Yes.

    Note: If you select No, the data is imported into ENVI and deleted from IDL.

  4. Click OK to import the selected variables.

    All one-dimensional variables are placed in a plot window; the 2D and 3D variables appear in the Available Band List as memory items.

Export to IDL Variables


Use Export to an IDL Variable to export and/or subset a band or file to an IDL variable.

  1. From the Toolbox, select Raster Management > Export to an IDL Variable. The Export to IDL Input File/Band dialog displays.
  2. Select an input file or band and perform optional spatial subsetting and spectral subsetting.
  3. In the Export Variable Name dialog, select one of the following options:
    • If the variable was previously defined, select on the name in the Select variable to receive export list.
    • If the variable is a new one, enter the name of an undefined ENVI variable in the New Variable Name field.
  4. Click OK. The exported data is available to use at the ENVI command line.

Landsat MSS Aspect


Use Landsat MSS Aspect to adjust the aspect ratio by applying nearest neighbor resampling to a regular grid. Landsat MSS image data typically contains geometric distortions caused by oversampling in the scan direction. The actual pixel sizes are approximately 79 x 79 meters, but the instrument samples at 57 meter intervals in the scan direction. Because of this oversampling, an adjustment of the aspect ratio by the factor 57/79=0.72 is required.

  1. From the Toolbox, select Raster Management > Data-Specific Utilities > Landsat MSS Aspect. The Input File dialog appears.
  2. Select an input file and perform optional spatial and spectral subsetting, then click OK. The Aspect Correction Parameters dialog appears.
  3. Select output to File or Memory.
  4. Click OK.

Landsat MSS Deskew


Landsat MSS image data processed prior to 1978 typically contains systematic distortions caused by earth rotation and scan skew. Use Landsat MSS Deskew to remove the skew by offsetting groups of scan lines based on the relationship between the orbital characteristics and latitude-dependent earth rotation characteristics.

  1. From the Toolbox, select Raster Management > Data-Specific Utilities > Landsat MSS Deskew. The Input File dialog appears.
  2. Select an input file and perform optional spatial and spectral subsetting, then click OK. The Deskewing Parameters dialog appears.
  3. Enter the latitude of the MSS scene center into the Latitude Degrees, Latitude Minutes, and Latitude Seconds field.
  4. Select output to File or Memory.
  5. Click OK.

Raster Dicer


Use the Dice Raster tools to separate a raster into tiles based on tile count, distance, pixel count, or a vector shapefile.

Dice Raster by Tile Count

Use Dice Raster by Tile Count to separate a raster into a specified number of tiles in the X and Y direction.

In most cases, the number of pixels (in both directions) will not be divisible by the specified number of tiles. For example, suppose that an image has 10 rows and 10 columns and you want to separate it into 3 tiles in the X and Y directions. Since 10 divided by 3 is 3.333, ENVI rounds up to the nearest integer (4) when creating the tiles. The last tile in each column and row will have smaller dimensions. The following figure shows how the tiles are created:

You can also write a script to perform this type of dicing using the ENVIDiceRasterByTileCountTask routine.

Follow these steps:

  1. From the Toolbox, select Raster Management > Raster Dicer > Dice Raster by Tile Count. The Dice Raster by Tile Count dialog appears.
  2. Select an input file and perform optional spatial and spectral subsetting.
  3. Enter the Number of X Tiles and Number of Y Tiles.
  4. To write the output files to disk, select the File radio button and specify an output directory. To produce output in memory only, select the Virtual Raster(s) radio button.
  5. Enable the Output Tile Grid Vectors option to create a shapefile that shows the tile boundaries. The shapefile will save to the directory indicated by the ENVI Temporary Directory preference.
  6. Enable the Preview check box to see a preview of the settings before you click OK to process the data. The preview is calculated only on the area in the Image window and uses the resolution level at which you are viewing the image. See Preview for details on the results.
  7. Enable the Display result check box to display the tiled rasters in the Image window when processing is complete. Otherwise, if the check box is disabled, the rasters can be loaded from the Data Manager.
  8. Click OK. ENVI adds the tiled rasters to the Data Manager and, if the Display Result check box was enabled, adds the layers to the Layer Manager and displays them in the Image window. The output directory will contain the tiled rasters. Their filenames contain the root name of the input raster with the row/column index appended in the form of RxCx. For example, R2C3 means row 2 and column 3.

Dice Raster by Distance

Use Dice Raster by Distance to separate a raster into tiles based on a specified distance. In most cases the tiles in the last row and column will be smaller than the specified distance, as the following example shows:

You can also write a script to perform this type of dicing using the ENVIDiceRasterByDistanceTask routine.

Follow these steps:

  1. From the Toolbox, select Raster Management > Raster Dicer > Dice Raster by Distance. The Dice Raster by Distance dialog appears.
  2. Select an input file and perform optional spatial and spectral subsetting.
  3. Enter a Tile Distance.
  4. Select the Distance Units from the drop-down list.
  5. To write the output files to disk, select the File radio button and specify an output directory. To produce output in memory only, select the Virtual Raster(s) radio button.
  6. Enable the Output Tile Grid Vectors option to create a shapefile that shows the tile boundaries. The shapefile will save to the directory indicated by the ENVI Temporary Directory preference.
  7. Enable the Preview check box to see a preview of the settings before you click OK to process the data. The preview is calculated only on the area in the Image window and uses the resolution level at which you are viewing the image. See Preview for details on the results.
  8. Enable the Display result check box to display the tiled rasters in the Image window when processing is complete. Otherwise, if the check box is disabled, the rasters can be loaded from the Data Manager.
  9. Click OK. ENVI adds the tiled rasters to the Data Manager and, if the Display Result check box was enabled, adds the layers to the Layer Manager and displays them in the Image window. The output directory will contain the tiled rasters. Their filenames contain the root name of the input raster with the row/column index appended in the form of RxCx. For example, R2C3 means row 2 and column 3.

Dice Raster by Pixel Count

Use Dice Raster by Pixel Count to separate a raster into tiles based on number of pixels. In most cases the tiles in the last row and column will be smaller than the specified distance, as the following example shows:

You can also write a script to perform this type of dicing using the ENVIDiceRasterByPixelTask routine.

  1. From the Toolbox, select Raster Management > Raster Dicer > Dice Raster by Pixel Count. The Dice Raster by Number of Pixels dialog appears.
  2. Select an input file and perform optional spatial and spectral subsetting.
  3. Enter a value for Number of X Pixels and Number of Y Pixels.
  4. To write the output files to disk, select the File radio button and specify an output directory. To produce output in memory only, select the Virtual Raster(s) radio button.
  5. Enable the Output Tile Grid Vectors option to create a shapefile that shows the tile boundaries. The shapefile will save to the directory indicated by the ENVI Temporary Directory preference.
  6. Enable the Preview check box to see a preview of the settings before you click OK to process the data. The preview is calculated only on the area in the Image window and uses the resolution level at which you are viewing the image. See Preview for details on the results.
  7. Enable the Display result check box to display the tiled rasters in the Image window when processing is complete. Otherwise, if the check box is disabled, the rasters can be loaded from the Data Manager.
  8. Click OK. ENVI adds the tiled rasters to the Data Manager and, if the Display Result check box was enabled, adds the layers to the Layer Manager and displays them in the Image window. The output directory will contain the tiled rasters. Their filenames contain the root name of the input raster with the row/column index appended in the form of RxCx. For example, R2C3 means row 2 and column 3.

Dice Raster by Vectors

Use Dice Raster by Vectors to separate a raster into tiles based on the spatial extent of individual vector records. The number of resulting tiles will be equal to the number of separate vector records.

You can also write a script to perform this type of dicing using the ENVIDiceRasterByVectorTask routine.

  1. From the Toolbox, select Raster Management > Raster Dicer > Dice Raster by Vectors. The Dice Raster from a vector Shapefile dialog appears.
  2. Select an input file and perform optional spatial and spectral subsetting.
  3. Select an input vector file that will be used to create the tiles.
  4. To write the output files to disk, select the File radio button and specify an output directory. To produce output in memory only, select the Virtual Raster(s) radio button.
  5. Click OK. ENVI adds the tiled rasters to the Data Manager and, if the Display Result check box was enabled, adds the layers to the Layer Manager and displays them in the Image window. The output directory will contain the tiled rasters. Their filenames contain the root name of the input raster with "Areaxx" appended, where xx is the vector record number.

Layer Stacking


Use Layer Stacking to build a new multi-band file from georeferenced images of various pixel sizes, extents, and projections. The input bands will be resampled and re-projected to a common user-selected output projection and pixel size. The output file will have a geographic extent that either encompasses all of the input file extents or encompasses only the data extent where all of the files overlap.

You can write a script to perform layer stacking using a combination of ENVIMetaspectralRaster and ENVISpatialGridRaster, or a combination of ENVIBuildBandStackTask and ENVIRegridRasterTask.

  1. From the Toolbox, select Raster Management > Layer Stacking.

  2. The Layer Stacking Parameters dialog appears.

  3. Click Import File. The Input File dialog appears.
  4. Select an input file and perform optional spatial and spectral subsetting, then click OK. The Layer Stacking Parameters dialog appears. ENVI adds the input file to the Selected Files for Layer Stacking list.
  5. Repeat the file selection using the Import File button for each input file to include in the new output file.

  6. Select Inclusive or Exclusive to specify the output file range:
    • Inclusive: Creates an output file with a geographic extent that encompasses all the input file extents.
    • Exclusive: Creates an output file that contains only the data extent where all the files overlap.
  7. Select output to File or Memory.
  8. Select an output map projection from the list.
  9. Enter the X Pixel Size and Y Pixel Size. Enter the pixel sizes in the units selected under the map projection section.
  10. From the Resampling drop-down list, select a resampling method:
    • Nearest Neighbor: Uses the nearest pixel without any interpolation to create the warped image.
    • Bilinear: Performs a linear interpolation using four pixels to resample the warped image.
    • Cubic Convolution: Uses 16 pixels to approximate the sinc function using cubic polynomials to resample the image. Cubic convolution resampling is significantly slower than the other methods.
  11. Click OK. ENVI adds the resulting output to the Layer Manager.

New File Builder


Use New File Builder to create an ENVI-format file from a combination of ENVI files, external (foreign) files, or memory items.

  1. From the Toolbox, select Raster Management > New File Builder. The New File Builder dialog appears.

  2. Click Import File. The Create New File Input File dialog appears.
  3. Select one or more files to include and perform optional spatial and spectral subsetting. You can subset a group of files if they are the same size; the subset is applied to each file.
  4. Repeat the file selection using the Import File button for each input file to include in the new file. Input files are listed in the Selected ENVI Files for New File list.
    • To delete a file from the list in the New File Builder dialog, select the filename and click Delete.
    • To change the order in which the files and/or bands are imported, click Reorder Files to open the Reorder Files dialog, and click on a filename or band name and drag it to the desired position in the list.
    • To remove the component files, use the Remove Superfluous Files? toggle button to select Yes (remove files), or No, next to the text label.

      Note: Removing component files physically removes the files from the Layer Manager and the disk. If transferring memory items to the new file and you select Remove Superfluous Files? the items are deleted from memory when the new file is created. If transferring all of the bands from a disk file to the new file and you select Remove Superfluous Files? the original disk file is physically deleted from the disk when the new file (either memory or disk file) is created.

  5. Select output to File or Memory.
  6. Click OK to build the new file. ENVI creates the file in BSQ format.

Replace Bad Lines


Use Replace Bad Lines to replace bad data lines in image data. You must identify the position of the lines to replace before running the function by using the Cursor Location/Value tool.

Note: Use the Spatial Pixel Editor to interactively fix bad lines.

  1. From the Toolbox, select Raster Management > Replace Bad Lines.
  2. Select an input file and perform optional spatial and spectral subsetting, then click OK. The Bad Lines Parameters dialog appears.
  3. In the Enter Bad Line field, specify which bad lines to replace and press Enter.
  4. The line appears in the Selected Lines list.

    • To remove that line from the list, select the line.
    • To save the line coordinates to a file, click Save.
    • To restore the coordinates from a previously saved file, click Restore.
    • To clear the list of lines to replace, click Clear.
  5. In the Half Width to Average field, enter the number of adjacent lines to use as an average for calculation of the replacement line. The value is symmetrical around the line to replace. For example, the value 2 means that two lines on either side of the selected line will be averaged to calculate the replacement.
  6. Click OK. The Bad Lines Output dialog appears.
  7. Select output to File or Memory.
  8. Click OK.

Resize Data


Use Resize Data to set x/y factors, output pixel size, and resampling values for an output raster file.

See Spatial Subsetting.

  1. From the Toolbox, select Raster Management > Resize Data. The Resize Data Input File appears.
  2. Perform optional spatial subsetting.
  3. Click OK. The Resize Data Parameters dialog appears.
  4. Either enter the number of Samples and Lines in the corresponding fields, or enter the multiplicative x and y enlargement or reduction factors in the xfac and yfac fields and press Enter. The Output Size field updates.
  5. Note: If your image contains map information, you can determine the number of output sample and lines based upon the desired output pixel size by clicking Set Output Dims by Pixel Size.

    • If the xfac and yfac values are greater than or equal to 1, select Nearest Neighbor, Bilinear, or Cubic Convolution, from the Resampling drop-down list (see Warp and Resample).
    • If the xfac and yfac values are less than 1, select from Nearest Neighbor or Pixel Aggregate resampling options.
    • You can control x and y scales independently. Enter values less than 1 to reduce the image and values greater than 1 to enlarge the image. The number of output samples and lines are updated.
    • Nearest Neighbor resampling uses the nearest pixel value as the output pixel value.
    • Pixel Aggregate resampling averages all the pixel values that contribute to the output pixel. If you enter 0.5 for both xfac and yfac, the output pixel values are calculated by averaging the four input pixel values.
  6. Select output to File or Memory.
  7. Click OK.

Rotate/Flip Data


Use Rotate/Flip Data to perform several standard image rotations, including 0, 90, 180, and 270 degrees with or without transposition. (Here, transpose means that the dimensions of the array are swapped.) Alternatively, you can specify the exact angle of the desired rotation. Rotating images is useful for orienting images before registration.

Note: To flip an image vertically, where the pivot line is a horizontal running through the middle of the image, choose 270 degrees with transpose. To flip an image horizontally, where the pivot line is a vertical running through the middle of the image, choose 90 degrees with transpose.

You can also write a script to flip raster data using the ENVIMirrorRaster routine. To transpose raster data, use the ENVITransposeRaster routine.

  1. From the Toolbox, select Raster Management > Rotate/Flip Data. The Input File dialog appears.
  2. Select an input file and perform optional spatial and spectral subsetting, then click OK. The Rotation Parameters dialog appears. This dialog varies slightly depending on whether you use a standard IDL rotation or an exact rotation angle.
  3. Initially, some letters and numbers are printed horizontally (normal text orientation) in the box in the upper-right corner of the dialog. The orientation of the numbers shows schematically the orientation of the output image with the selected rotation and/or transpose applied.

  4. Select from the following rotation options:
    • To apply a standard rotation (0, 90, 180, or 270 degrees), click Standard and select the rotation.
    • To flip the x and y coordinates of the image, click the Transpose toggle button to Yes.
    • To specify the exact rotation angle desired, enter a value in the Angle field (angles are measured clockwise from horizontal) and press Enter.
  5. Select the resampling algorithm to use to calculate the output image from the Resampling drop-down list. The choices are Nearest Neighbor, Bilinear Interpolation, or Cubic Convolution.
  6. Select output to File or Memory.
  7. Click OK. ENVI adds the resulting output to the Layer Manager.

Stretch Data


Use Stretch Data to perform file-to-file contrast stretching. The data stretching function is a flexible method for changing the data range of a given input file. You have full control over both the input and output histograms and the output data type (byte, integer, floating-point, and so forth).

  1. From the Toolbox, select Raster Management > Stretch Data.
  2. Select an input file and perform optional spatial and spectral subsetting, then click OK. The Data Stretching dialog appears.
  3. To calculate the statistics based on a statistics subset or the area under an ROI, click Stats Subset.
  4. Select the Stretch Type (Linear, Equalize (histogram equalized), Gaussian, and Square Root) from the appropriate radio button.
  5. If you select Gaussian, enter a standard deviation in the Stdv field.

  6. Select a Stretch Range value of By Percent or By Value from the appropriate radio buttons.
  7. Enter the minimum and maximum values in the Min and Max fields, respectively, to control the input data range.
  8. Set the Output Data Range in the Min and Max fields. The values must match the ranges of the data type selected from the Data Type drop-down list (see next). If out-of-range values are entered, low values are automatically corrected to the minimum and high values are automatically corrected to the maximum of the selected data type.
  9. From the Data Type drop-down list, select the appropriate data type (byte, integer, unsigned integer, long integer, unsigned long integer, 64-bit integer and unsigned 64-bit integer, floating-point, double precision, complex, or double complex).
  10. Select output to File or Memory.
  11. Click OK. If no statistics file exists for the selected input file, ENVI calculates the image statistics before data stretching and an Image Statistics window shows the percent processing complete as a slider that moves from 0 to 100%. If a statistics file already exists (or when the image statistics are calculated) a Data Stretching window shows the percentage of data stretching completed. When complete, ENVI adds the resulting file to the Layer Manager.

Subset Data via ROIs


Use Subset Data from ROIs to subset your data into a rectangle that contains the selected ROIs. The rectangle is the smallest rectangle that will fit the ROI. You can mask the pixels in the rectangle that do not fall within the ROI.

  1. From the Toolbox, select Raster Management > Subset Data from ROIs. The Select Input File to Subset via ROIs dialog appears.
  2. Select an input file and perform optional spatial subsetting, then click OK. The Spatial Subset via ROI Parameters dialog appears.
  3. From the Select Input ROIs list, select the ROIs to include in the subset.
  4. Use the Mask pixels outside of ROI? toggle button to select whether or not to mask pixels outside of the selected ROI. If you select Yes, enter a Mask Background Value.
  5. Select output to File or Memory.
  6. Click OK. ENVI adds the resulting output to the Layer Manager.



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