{"id":556,"date":"2018-11-30T22:29:42","date_gmt":"2018-11-30T22:29:42","guid":{"rendered":"https:\/\/www.ssec.wisc.edu\/mcidas\/?page_id=556"},"modified":"2023-12-15T20:25:57","modified_gmt":"2023-12-15T20:25:57","slug":"mcstretch_info","status":"publish","type":"page","link":"https:\/\/www.ssec.wisc.edu\/mcidas\/software\/x\/info\/mcstretch_info\/","title":{"rendered":"McIDAS-X Expanded Stretch Feature"},"content":{"rendered":"

McIDAS-X versions 2017.2 and later include improvements to visualize more bit-depth in the data and provide more contrast in the images.<\/p>\n

This expanded stretch feature was added to increase the detail shown in visible, water vapor and short-wave infrared imagery when displayed with IMGDISP from an updated ADDE server or copied to a 1-byte Area file using commands like IMGCOPY with STYPE=VISR or IMGREMAP. This is done by expanding the range of data values stretched out over the 8-bit brightness values in the higher reflectances in visible bands, and in the very hot temperatures in short-wave IR bands. The range of data values is narrowed in both colder and warmer temperatures in the water vapor bands.<\/p>\n

Additional information, including how to use the expanded stretch feature, which satellite and band combinations use the feature, and how to modify existing enhancement tables to work with imagery, is found in the Details<\/em> section below<\/a>.<\/p>\n

WHAT YOU WILL SEE<\/h2>\n
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Water Vapor Bands<\/h3>\n
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The example below shows a GOES-16 band 8 water vapor image displayed in McIDAS-X version 2017.2 on the left, and the same image displayed in version 2017.1 on the right. Note that the expanded stretch feature in 2017.2 (left image) results in more contrast due to using a smaller range of data values stretched out over the 8-bit brightness values.<\/p>\n\n\n\n
NEW<\/b><\/td>\nPREVIOUSLY<\/b><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
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\"Band<\/a><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div><\/div>\n<\/p><\/div>\n
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Visible Bands<\/h3>\n
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The example below shows a GOES-16 band 2 visible image displayed in McIDAS-X version 2017.2 on the left, and the same image displayed in version 2017.1 on the right. Note that the expanded stretch feature in 2017.2 (left image) shows more detail in the highly reflective cloud tops near the center of the image due to its use of a larger range of data values stretched out over the 8-bit brightness values.<\/p>\n\n\n\n
NEW<\/b><\/td>\nPREVIOUSLY<\/b><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
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\"Band<\/a><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

<\/a> The improved contrast is not easy to see in the grayscale image, but adding a color enhancement shows the detail in the clouds that is washed out and white in the previous versions of McIDAS. The example below shows the same GOES-16 band 2 visible images as the example above, but with a color enhancement applied.<\/p>\n

Since the enhancement tables map colors to 8-bit brightness values and the brightness values had changed, we needed to update the enhancement table to use the new values. The enhancement on the left was created from the one on the right by using the new EU CONV option to convert an enhancement table created prior to 2017.2 to work with the expanded stretch feature. It now maps the same image values to the same display colors\/shades as it did without the expanded stretch, as well as showing the improved contrast.<\/p>\n\n\n\n
NEW<\/b><\/td>\nPREVIOUSLY<\/b><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
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\"EU<\/a><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div><\/div>\n<\/p><\/div>\n
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Short-wave IR Bands<\/h3>\n
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The changes in the IR are not as dramatic visually, but make automated tasks like fire detection much easier to accomplish. The example below shows a GOES-16 band 7 short-wave IR image displayed in McIDAS-X version 2017.2 on the left, and the same image displayed in version 2017.1 on the right. Note that the expanded stretch feature in 2017.2 (left image) shows additional detail because the temperatures in the warmer regions are stretched out over the 8-bit brightness values.<\/p>\n\n\n\n
NEW<\/b><\/td>\nPREVIOUSLY<\/b><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
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\"Band<\/a><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

The example below shows the same GOES-16 band 7 short-wave IR images as above, but zoomed in on the dark fire region in the upper-right quarter of the image and enhanced to show the subtle differences in the pixel values of the fire region. In particular, there is a larger range of brightness temperature values in the perimeter of the fire. In very hot regions that are likely fires, the expanded stretch lets you more easily identify the hottest regions versus those that are slightly cooler.<\/p>\n\n\n\n
NEW<\/b><\/td>\nPREVIOUSLY<\/b><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
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\"Band<\/a><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

<\/a><\/h2>\n<\/p><\/div>\n<\/p><\/div>\n
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New Command Options<\/h3>\n
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If you have old enhancement tables that you use with water vapor, visible, or short-wave IR images, a warning message will be displayed if you try to use the old enhancement table with an image displayed with the expanded stretch. Use the EU CONV<\/b> command to covert your old enhancement table to one that will map the same color to the same data values as it did previously.<\/p>\n

If you prefer your images to be displayed with the pre-2017.2 stretch, or need it to match the grayscale enhancement of an older image, use the MCS=ORIG<\/b> keyword in your IMG* command (see the Details<\/a> below).<\/p>\n

<\/a><\/h2>\n<\/p><\/div>\n<\/p><\/div>\n
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Details<\/h3>\n
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Scanning instruments on newer satellites are often more sensitive than on earlier satellites and thus record more detailed information in their imagery. For example, the visible bands in GOES-16 ABI and Himawari-8 AHI data can detect reflectance\/albedo values up to 120%, and the short-wave IR bands for those satellites can record higher maximum temperatures (e.g., near or above 400 K).<\/p>\n

In order to better utilize and display this data, a new feature was added to McIDAS-X beginning with version 2017.2. The new feature, called the expanded stretch, increases the detail shown in certain visible, water vapor and short-wave IR imagery when displayed with IMGDISP or copied to a 1-byte Area file using commands like IMGCOPY with STYPE=VISR or IMGREMAP. The expanded stretch was added for all of the operational satellites, so that the grayscale images would match for all satellites.<\/p>\n

The bullets below describe how to use the expanded stretch feature, which satellite and band combinations use the feature, and how to modify existing enhancement tables to work with imagery displayed using the expanded stretch.<\/p>\n