PNG is Portable Network Graphics (pronounced "Ping"), a well-known image format used for graphics.  It does not provide coordinate system information.  When exporting, .prj and .mapmeta files are written.  See the Exporting topic.



By right-clicking into the Import dialog and choosing View we can ask Windows to display the files as Large icons instead of as Details.



Windows will then preview the contents of .png files as icons.


To import from PNG format:


  1. Choose File-Import from the main menu.

  2. In the Import dialog browse to the folder containing data of interest.

  3. Double-click the file ending in .png for the data of interest.

  4. A table and an image will be created.



We can double-click on images that are created to view them.   



This particular image shows the portrait of Ginevra de' Benci by Leonardo da Vinci.   It is not georegistered and has no coordinate system assigned.  By default, we can assign it a Pseudo Mercator projection, which is meaningless other than to provide a coordinate system for the pixels.

Exporting to PNG

Exporting an image to PNG automatically creates an RGB, an RGBA, a grayscale or a palette image depending on the number of channels in the tile and the settings for the image in the Style pane.   See the About Images topic for a discussion of different image types.



Consider the ginevra image imported above.  It is an RGB image that uses three channels, as seen in the Style dialog.  It will be exported into .png format as an RGB image.



Next, consider the ginevra grayscale image seen above.  It is an image that has only one channel, as seen in the Style dialog, which results in a grayscale image.  It will be exported into .png format as a grayscale image.  If we import a grayscale image, or if we create a single-channel grayscale image from a three or four channel image, that will export as a grayscale image.



We have taken the ginevra grayscale image and have used the Style pane to create a palette-driven display using Channel 0 as the index channel.  It will be exported into .png format as a palette image, also called an index image by some graphics editors, such as Photoshop.  The data in the image is the same, but because we are using the Style pane to specify how that data should be interpreted, together with a palette, the image is exported as a palette image.



Using graphics files -  Images in formats such as BMP, PNG, ICO, etc.,  that do not provide coordinate system information can be handy as illustrations in layouts or for other purposes, such as sources for bitmap symbols in Style dialogs..    Manifold project files are so efficient that we can keep libraries of many images for fast viewing in Manifold, even if we do not intend to work with them in GIS.   We can also use Manifold to convert images between different formats, importing an image as one format and exporting it as another.


Ginevra and Leonardo - See the Example: Change the Contrast of an Image topic for historical notes on Ginevra de' Benci and Leonardo da Vinci.


See Also



Style: Bitmap Symbols