How to Cut and Paste Images into Mosaics


You can make a mosaic by combining either individual raw Viking images or the MDIMs. However, several things should be kept in mind. Both the raw images and the MDIMs are in Sinusoidal projection. This means that latitudes are parallel to each other, but longitudes are distorted. The distortion gets worse the further you go from the equator. A global sinusoidal projection of Mars would look like this.

In order to make the individual images rectangular, the left and right boundaries of the image area are filled with black pixels. In NIH Image, only rectangular images or the "Region Of Interest" (ROI) can be cut or copied and pasted to form mosaics.

Making a Montage

There are two ways of making "mosaics" within Image. A quick and easy way to make a mosaic, although the final result may not be all that pleasing to the eye, is to make a montage. To make a montage, first open all the images that will comprise the mosaic.. It is important to first open the file that will be in the upper left corner of the mosaic. Next, open the file that will be pasted to the right of the first file and so on. If there is to be another row, keep on opening images in order from left to right and top to bottom, just like reading a book.

Once all image files have been open in the right order, pull down the STACKS menu and select "Windows to Stack". This action will create a stack of all the open image files one on top of the other.

The number of slices in the stack is equal to the number of image files open. Now pull down the STACKS menu again and select "Make Montage". A window will appear that asks for the number of rows and columns desired.

For the example here, only 1 row and 2 columns are needed for the montage. Deselect the "Number slices" and "Borders", then select "OK" and you should now have a montage like this.

Notice the black pixels where the 2 images were joined at the bottom. This occurs because the images are not perfectly rectangular. If the images are far from being rectangular, then this is the best that can be done as image projections can't be easily changed within NIH Image. However, sometimes if the black area is not too large (as in this example), you can paste the images manually as detailed below.

Making Mosaics by the Cut and Paste Method

In general, a better looking mosaic can be made by selecting a "Region of Interest" (ROI) within the image and manually cutting and pasting the ROI to another image file. In this method, you do not need to have all of the image files that will comprise t he mosaic open at the same time or opened in the right order as in the previous method. However, you do need to determine the total width and height of your mosaic in pixels. To do this, add up the total number of pixels in the ROI's (parts of image f iles) that will make up the mosaic by moving the mouse from left to right across each image or ROI to determine the width of that image in pixels and then from bottom to top to determine the height of the image. The pixel number is located in the Info window as shown below. Another way to determine the width and height of the image, particularly if you plan to use the whole image, is to go to the finder and select FILE - Get Info . As shown below, a dialog box will open that will h ave the height and width of the image file in pixels.

When using the method where the mouse cursor is dragged across the image to obtain the height and width of the ROI, the actual pixel number is again with reference to the lower left corner of the image which is the designated origin. To obtain the image width in pixels, subtract the pixel number of the left image boundary from the pixel number at the right boundary to obtain the actual image width. Do the same to determine the actual image height. Open a new window by selecting the FILE - New menu. Enter the width and height in pixels of the planned mosaic as in the example below.

An new (blank) window should now appear on your screen. Use the WINDOWSmenu to move between the opened image files. Go to the image that will be in the upper left corner of the mosaic. Use the "Select" tool to delineate the ROI within the image as shown below.

Select EDIT - Copy and then use the WINDOW menu to move back to the new mosaic window. Select EDIT - Paste to paste the ROI to the new mosaic window as shown below.

The ROI should then appear in the new window and the image can then be dragged to the desired location in the upper left-hand corner of the mosaic. To paste the image to the desired location, simply click the mouse button outside of the ROI and the "marching ants" selection box should disappear. However, if this does not occur, select EDIT - Deselect. Repeat the same procedure for the image file or ROI that will be located to the right of the newly pasted segment in the mosaic window. Drag the second ROI and align the images so that the features of the second image or ROI line up with the features on the first. Repeat the procedure until all desired ROIs are incorporated into the new mosaic.

Save your image as a tiff or pict file to your own hard drive or floppy drive. You will then be able to read in your image file into NIH Image using just the FILE - Open command.

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