Displaying image layers

Note:

The functionality described in this topic is available in Portal for ArcGIS 10.2.1 and later releases.

Using the map viewer, you can create and display your imagery on the web. As the author of a web map, you decide how the rest of the world will visualize your imagery.

When you add an image layer to a web map, the map initially uses the default display settings of the image service. If you want to change the appearance and ordering of the images in the display, you can change the image display, the image display order, and the image quality.

Image display

You can change the image display by using a predefined template or setting the band combination and stretch parameters.

Using a predefined template

When you publish an image service, you can predefine the image display with templates. You might use a predefined template for several reasons:

• Display a clear and good view of the data
• Display the images without clouds
• Highlight certain features within the image

You can choose any of the predefined templates that best suits your web map.

Follow these steps to choose a predefined image display template.

Steps:

1. Open the web map with the image layer you want to change in the map viewer.
2. Click the Contents button in the Details panel.
3. Click the arrow to the right of the layer name and click Image Display. The Image Display pane appears in the left side of the map viewer.
4. Click the Renderer drop-down arrow and choose the display template you want to use.
5. Click the Apply button.

The web map displays the image as set by the template you choose. These templates cannot be edited within the web map.

Using the user-defined renderer

The band combination allows you to specify which bands are displayed using the red, green, and blue color composite scheme. The different color combinations display your imagery with various color effects. You can display your data in a natural color (red, green, and blue), which displays the layer as you would normally see it. Other color combinations can highlight vegetation, urban areas, water, and other features.

The stretch parameters improve the appearance of your image by using various contrast enhancements. The following contrast enhancements determine the range of values that are displayed.

• None—No additional image enhancements will be performed.
• Minimum and Maximum—Display the entire range of values in your image.
• Standard Deviation—Display values between a specified number of standard deviations.
• Percent Clip—Set a range of values to display. Use the two text boxes to edit the top and bottom percentages.

You can also make additional adjustments to the dynamic range adjustment (DRA) and the gamma factor.

• Dynamic Range Adjustment—Performs one of the above stretches but limits the range of values to what is currently in the display window. This option is always turned on if the image service does not have global statistics.
• Gamma—Stretches the middle values in an image but keeps constant the extreme high and low values.

Follow these steps to change the image display.

Steps:

1. Open the web map with the image layer you want to change in the map viewer.
2. Click the Contents button in the Details panel.
3. Click the arrow to the right of the layer name and click Image Display. The Image Display pane appears in the left side of the map viewer.
4. Click the Renderer drop-down arrow and choose a user-defined image display.
5. Adjust the Red, Green, Blue composite with the bands you want to display.
6. Click the Stretch drop-down arrow and choose the stretch type to use.
   • None
   • Minimum and Maximum
   • Standard Deviation
   • Percent Clip
   1. Additionally, adjust any of the parameters for that particular stretch.
7. Click the Apply button.

The web map displays the image with the user-defined parameters you set.

Image display order

An image service published from a mosaic dataset contains one or more images. These images are mosaicked on the fly and behave like a single image when a user browses the service. When creating a web map, you select how the map will display for your audience. You can determine the image order and how to resolve overlapping areas. Image order refers to how to select an image when there are multiple images over the same area. You can also determine how to display areas of images that overlap one another.

As the author, you set the Priority Ordering Method; this controls which images are visible and the image order. Images in an image service are visible at certain scales.The visibility range corresponds to the minimum pixel size (MinPS) and maximum pixel size (MaxPS) in the image attributes. The visiblity setting is always honored except when the A list of images option is chosen.

• Only scale—Use this option to prioritize the image order by the scale of the images. For images that are at the same scale, the ObjectID within the image attributes determines their display order.
• An attribute—Select an attribute to determine the image order. The image with the highest value according to its attribute will be displayed on top. For example, if you want to show the most recent images, you can display the images based on their acquisition date. Use the calendar to select the acquisition date. Another common attribute to use is the percentage cloud cover to get the clearest image possible.
• Image center closest to the view center—As your audience browses through a mosaicked raster layer, the images that are displayed will change. The images with their image centers closest in distance to the center of the screen display on top. This is useful if your audience is interested in the stationarity of features.
• Fixed order with the most northwest on top—The order is based on the center of each image's distance to the north-west corner of the mosaicked raster layer. Since this presents a static display, it is useful when you do not want the images to change.
• Sensor location closest to view center—Displays the images with the least distortion. When a sensor captures an image, the point directly overhead of the image is known as the nadir point, which tends to have the least distortion. The images with their nadir point closest in distance to the center of the screen display on top.
• Defined seamlines—You need to have seamlines already created if you want your audience to have access to this option. Images are prioritized based on your existing seamlines. If you choose this option, you should use the Blend of pixel values to resolve any overlapping pixels.
• A list of images—If you're interested in a small number of images, you can explicitly list them using a comma-delimited list in the order you want them to be displayed. This method bypasses image visibility constraint and forces the listed images to display at any scale, for example, 1, 2, 3.

Check the Reverse the order box to reverse the order the priority sets.

After setting the Priority Ordering Method, there may be instances where two or more images overlap. You can resolve overlapping areas with the following settings:

• Only highest priority—Use the pixel value from the image that has the highest priority as set by the Priority Ordering Method.
• Minimum of pixel values—Use the lowest pixel value.
• Maximum of pixel values—Use the highest pixel value.
• Average of pixel values—Use the mean pixel value.
• Blend of pixel values—Use the blend option for overlapping areas to create a smooth transition along seamlines.

Follow these steps to change the image priority order:

Steps:

1. Open the web map with the image layer you want to change in the map viewer.
2. Click the Contents button in the Details panel.
3. Click the arrow to the right of the layer name and click Image Display Order. The Image Display Order pane appears in the left side of the map viewer.
4. Select the method to prioritize imagery.
5. Optionally, reverse the order, if necessary, by clicking the Reverse the order box.
6. Select the method for resolving overlapping pixels.
7. Click the Apply button.

The web map displays the images with the visibility and priority parameters you set.

Setting image quality

There are tradeoffs between performance and image layer quality because they are inversely related. Higher-quality images will be larger files and will affect performance speed. Performance is also dependent on your connection speed. There are several options designed to meet your needs and bandwidth capabilities.

• Performance—Compresses into a JPEG format at 50 percent quality. Assuming the original image has dimensions of 1034 by 721 (approximately 2 MB), the transmitted size using this option is only 62K. This option does not support any transparency, so areas of no data will be displayed in black.
• Balanced—Compresses into a PNG32 when there are NoData pixels present in the current view and compresses into a JPEG format at 75 percent quality when there are no transparent pixels. Assuming the original image has dimensions of 1034 by 721 and no transparent pixels, the transmitted size using this option is 99K.
• Quality—Compresses into a PNG32 format when there are NoData pixels present in the current view and creates a JPEG compression at 95 percent quality when there are no transparent pixels. Assuming the original image has dimensions of 1034 by 721 and no transparent pixels, the transmitted size using this option is 277K.

In general, use the Quality or Balanced option. If you are on a network with low bandwidth, choose the Performance option. Note that choosing Performance will cause transparent pixels to be blacked out.

Follow these steps to change the image quality.

Steps:

1. Open the web map with the image layer you want to change in the map viewer.
2. Click the Contents button in the Details panel.
3. Click the arrow to the right of the layer name and click Image Quality.

   The Image Quality slider appears in the map viewer.

4. Use the slider to select the compression level.

The web map displays the image with the selected compression quality chosen.

Filter images

When you have multiple images in your image service, you can use attribute queries to filter the images displayed. Filtering image layers works similarly to filtering feature layers. For example, if you are working with the entire Landsat archive, but only want to see cloud-free images from Landsat-7 before its scan-line corrector went off, you could do that with a filter. One thing to note about image filtering is that the map scale may affect the visibility of filtered images.

To learn more about filtering, see Applying filters.

Show table/table options

You can display the table of the image layer. The table has metadata for each image, which can be useful for deciding which categories to use when filtering. You can also use the table to:

• Show selected records/ Show all records—Shows only the records you have selected from the layer.
• Center on the selection—Centers on the selected records in your layer.
• Clear the selection—Clears the images from the selection. They will remain visible on your map and in the table.
• Show/Hide columns—Choose which columns to display in the table.
• Select visible images—Select the images that are visible on the map.
• Display all images—Displays all of the images from your layer on your map.
• Display selected images—Display only the images that you have selected.

To learn more about tables, see Showing tables.

Legend

If your image service is shared on an ArcGIS 10.2 server or later, you can display a legend in your web map. The legend shows by default; however, there is an option to hide it.

To learn more about legends, see Viewing a legend.