Horizon Image

Creating a Horizon Image
by Dennis Allen

Here is a brief description of how to create a panoramic horizon image for either Software Bisque's TheSky v6 or StarryNight Pro v4.5. For this article, I'll be using an image called tt5a.jpg as a reference.

First you need to take pictures of your observing site. Make sure your camera tripod is level. Have some sort of marker indicating which way is true north (not magnetic). For our facility, the sidewalk just happens to run true north. Takes a roll of pictures, with good overlap between shots. For the tt5c image, John Augustin used his digital camera set at 30mm.

If you use 35mm film, try to get the print shop to keep all the prints at the same color balance. If not, I found Adobe Photoshop Elements does a good job of color correction. Just use [auto levels] to correct the color balance.

Once you have your prints scanned into the computer (300 dpi is good) and color balanced, you'll need to stitch them together. Use a 10000 by 1200 pixel area as a starting base. You could use Photoshop Elements, but I prefer Picture Windows Pro 3.1 (nice stitching feature). Start with an image that has true north. When stitching, try to keep your horizon on the same plain (# pixels from the bottom of the panoramic). Your last image should be another overlap of true north. Check whether the true north marker on the last image is on the same horizontal plain with the first image. If not, you might have to redo the last image by warping it (might also have to warp the first image).

Crop your panoramic so that your true north marker is split in half by the first and last images. Mask off your clouds, leaving only grass, tress, hills and buildings. Replacing the clouds with a single color makes the image easier to process (make sure color is not found in rest of image). Then resize your panoramic to be 5000 pixels in width and save it as a JPEG file.

When working with the JPEG, determine the pixel height of your image. For our example, the tt5c image came to 531 pixels high. Next, determine where your horizon line is located, in pixels. For tt5c, we have 271 pixels above and 260 pixels below the horizon. Now 5000 / 360 = 13.89 pixels per degree, so 531 pixels comes to 38.23 degrees (19.51 degrees above and 18.71 degrees below the horizon).

Starry Night Pro v4.5

To create a Starry Night horizon image, launch Photoshop Elements and load your JPEG file. Open the layers folder and rename the 'Background' layer to 'Layer 0'. That takes the lock off. Magic wand your masked area (cloud area) and edit->cut. In the layer folder, create a new layer called 'Layer 1' and drag it so it is listed before 'Layer 0'. Now do 'Save As', file type PSD, in the folder 'Program Files/StarryNight Pro 4.5/Sky Data/Horizon Panoramas'. Watch that you save with a file name similar to tt5c.psd, not tt5c.tif.psd or tt5c.jpg.psd (use the file->open dialog box to check and/or rename the file).

Now in the same folder, find an existing txt file and make a copy (if tt5c.psd is the image, tt5c.txt should be the txt file). Edit the txt file. For tt5c.txt, the main parameters are:

<SN_VALUE name="PanoName" value="tt5c">
<SN_VALUE name="ImageFileName" value="tt5c.psd">
<SN_VALUE name="ImageHeight" value="38.23">
<SN_VALUE name="UseImageAlpha" value="Yes">
<SN_VALUE name="ImageCentreDec" value="0">
<SN_VALUE name="ImageCentreRa" value="180.000000000000000000">

For a more complete description of this file, click here. After you launch StarryNight, open the options panel->local view->local horizon options. In the photorealistic/earth horizons list you should now be able to select tt5c. For your image, I suggest starting with a "ImageCentreDec" of 0. Increase the value until the image horizon meets with the actual horizon.

Note: If you ever change your psd file, delete the corresponding '*.psd_Cache' subfolder found in the 'Horizon Panoramas' folder. Otherwise, StarryNight won't know there was a change.

For the StarryNight image of the Muskegon Astronomical Society observatory, click here. You need to unzip this file in the folder 'Program Files/StarryNight Pro 4.5/Sky Data/Horizon Panoramas'. After you launch StarryNight, open the options panel->local view->local horizon options. In the photorealistic/earth horizons list you should now be able to select tt5c.

Software Bisque TheSky v6

With TheSky, you need to create a TIF file. Using Photoshop Elements, open up your JPEG file. Magic wand your masked area (cloud mask), then inverse the layer so that the horizon image itself is highlighted. From the Select pulldown, select 'save selection'. Name it 'Alpha 1' and save the layer. Now inverse your layer again to highlight the cloud area again and edit->cut. Do a 'Save As', file type TIFF, in the folder 'My Documents/Software Bisque/TheSky6/Horizons' (you want 'My Documents', not 'Program Files'). When you save your TIFF, use LZW compression, uncheck 'save image pyramid'. And again, save the file with a name similar to tt5c.tif, not tt5c.jpg.tif.

Note: Certain images will not display properly after Windows XP SP2 is installed. As I understand it, Software Bisque is aware of the problem and is working on it. In the meantime, make sure you save a TIFF file using LZW compression and that you do NOT check the [save image pyramid] option.

In the same 'Horizons' folder create a file with a *.horizon extension. For the image tt5c.tif, the file has to be called tt5c.horizon (not tt5c.horizon.txt). The file tt5c.horizon has the following text parameters:

ALT TOP = 19.5
ALT BOT = -18.71
AZIM = 0.0
TYPE = PANORAMA
TYPE = SHAPE=FALSE

Note: TheSky doesn't allow an ALT BOT of more than 19 degrees. So when you create your panorama, don't let the horizon rise beyond midpoint in the image.

After you launch TheSky, select View->Real Mode Options. Click on 'Horizon Image' and 'Advanced Options'. Do a browse and select your new *.horizon file. Apply and Save.

For a copy of the Software Bisque's TheSky image of the Muskegon Astronomical Society observatory, click here. You need to unzip this file in the folder 'My Documents/Software Bisque/TheSky6/Horizons'.After you launch TheSky, select View->Real Mode Options. Click on 'Horizon Image' and 'Advanced Options'. Do a browse and select the tt5c.horizon file. Apply and Save.

Conclusion

The tt5c image is the second panoramic I've tried. John Augustin's images don't suffer from as much vignetting as from my camera. And I finally got the the last image in this panoramic to line up right with the first image. Not perfect, but a start.

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This web page was last updated 04/03/08