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Orbit Multiresolution Image
The Orbit Multiresolution Image (*.omi) is Orbit's native multiresolution image and raster file storage format.
The OMI has been developed for encoding and fast viewing of raster and image resource of any size on any platform.
Structure
An OMI is a pyramid stored multiresolution image.
The compression rate is slightly less compared to other multiresolution image formats, but performance and speed of use is higher.
More information, see Wikipedia Pyramid Image Processing.
Reasons to use
- Highest performance for fast viewing of (large) image datasets.
- Support for black/white, grey-scale and color images
- Platform independent, can be used on Windows, Linux and Mac.
Create and Update
An OMI can be created via the Additional Tools :
- Convert Data : Convert one on one, one Image to one OMI (or other image storage file format)
- Optimize Data : Convert multiple Images to one OMI
Options and Compression
When creating an OMI, flowing options are available to define storage and compression.
Pixel Size
Define the number of bits (1, 8, 24 or 32) to be used to store one pixel of (raster or image) resource 1)
| Bits/Sample | Samples/Pixel | Bits/Pixel | Image type |
| 1 | 1 | 1 | Monochrome black-white |
| 8 | 1 | 8 | Grayscale |
| 8 | 3 | 24 | RGB (red green blue) |
| 8 | 4 | 32 | ARGB (alpha/transparency RGB) |
Pixel Size 1
A pixel can hold one sample with 2 possible values 0 (black) or 1 (white).
When using pixel size 1, it will be possible to set a threshold : Light, Medium or Dark.
Applying a threshold is a method to simplify an image to sets of pixels with corresponding values. The result is an image containing contiguous regions of the same value. This technique makes it easier to apply analysis.
- Light will favor light color values.
- Dark will aggregate dark color values.
Pixel Size 24
A pixel can hold 3 samples with a value between 0 .. 255.
Using pixel size 24 enables additional JPG compression quality parameters. :
- Lossless “fully recoverable”, no compression
- Lossy “with losses to quality”
- Smallest file
- Standard
- Quality
Lossy meaning “with losses to quality”. Approximate sample values will be stored with sample value compression rate 5:1 up to 20:1
Examples .jpg, .ecw, .sid
Lossless always returns the original data. Lossless meaning “fully recoverable”. The exact sample values will be stored.
Examples : .gif, .png, .bmp
It is advised to save images with a wide variety of colors (photos) with lossy compression (jpg).
Images with a limited variety (computer graphics, icons) should be saved lossless (png).
Pixel Size 8 and 32
No extra options.
Legend and Georeference
Optionally an OMI can be accompanied by an Image World File, Orbit Legend and Orbit Resource Descriptor in Orbit.