An 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 any size on any platform.
An OMI stores any image in an intelligent pyramid structure, see Multiresolution Image data.
An OMI can be created via the Map 2D Additional tools :
Also , an OMI can be created via the Process MM Imagery procedure, for creating OMIs from the original imagery in a run.
When creating an OMI, flowing options are available to define storage and compression.
Pixelsize
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) |
Pixelsize 1
A pixel can hold one sample with 2 possible values 0 (black) or 1 (white).
When using pixelsize 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.
Pixelsize 24
A pixel can hold 3 samples with a value between 0 .. 255.
Using pixelsize 24 enables extra quality parameters. :
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).
Pixelsize 8 and 32 have no extra format options.
When creating an OMI one need to choose the type of compression Lossless or Lossy (Smallest File, Standard or Quality).
A Lossy compression will use JPG compression techniques to store the multi-resolution images.
Optionally an OMI can be accompanied by an Image World File, Orbit Legend and Orbit Resource Descriptor in Orbit.