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IMGIMG: IMG files conversion and compression/decompression
IMGIMG: IMG files conversion and compression/decompression| Presentation and options | Dialog box of the application |
| Syntax |
The following IMG raster formats are supported by MiraMon:
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Subformat
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Bits per pixel
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Bytes per pixel
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Type of value
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Whole values (for integer numbers) or maximum and minimum values and number of significant figures (for real numbers)
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Examples of use
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bit
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1
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1/8
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integer
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[0,1]
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Mask image
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byte
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8
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1
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integer
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[0,255]
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Thematic cartography up to 256 categories, aerial or satellite imagery (black and white or color) up to 256 grey levels or 256 colors
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integer
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16
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2
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integer
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[-32768, 32767]
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Thematic cartography of more than 256 categories, several types of DTM, aerial or satellite imagery (black and white or color) of more than 256 grey levels or 256 colors
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unsigned integer
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16
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2
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integer
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[0, 65535]
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Same as "integer", but without negative values and more possible positive values
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long
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32
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4
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integer
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[-2147483648, 2147483647]
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Thematic cartography with links to databases
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real
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32
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4
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real
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(~-3.4E+38, ~3.4E+38)
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Several types of DEM that need single real precision (6 guaranteed significant figures) as temperature maps with tenth degree accuracy
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double
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64
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8
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real
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(~-1.7E+308, ~1.7E+308)
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Several types of DEM that need double real precision (15 guaranteed significant figures). In practice, double format is only used to intermediate calculations in which too much precision is needed, and not for final layers
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Except for the bit format, there also exist equivalent compressed RLE formats that use the improved "Run length encoding" algorithm. Some support is provided for bit-vell format (old-bit), which is the continuous bit data format, but only changes from bit-vell to byte-rle and from byte to bit-vell are permitted.
MiraMon supports two RLE formats, semicompressed and extracompressed. The semicompressed format, the standard in the literature, it is not usually used in MiraMon since extracompression is much better. If semicompression is desired it must be indicated using the additional parameter /NO_EXTRA. It is also necessary to bear in mind that for the compressed formats it is very helpful to use the /RLE_INDEX mode that generates a list of the initial line positions which is stored at the end of the file. This feature increases slightly the file size but allows faster access.
In compression and decompression the data format is maintained but in the cases of format changes it must be remembered that when passing to a format with a smaller range (for example from integer to byte) the values that fall outside the output range will be saturated. In other words, if passing from integer format without NoData to byte, then all values >255 will become 255 and the values <0 will be set to 0. This could also affect the NoData value. If this is within the output range then it will keep its value, but if it is outside the output range it will be saturated, and will reduce the range of valid values. In the example of conversion from integer to byte, a NoData value of -9999 will become 0 and the range of valid values will be [1,255].
It is also important to consider that in conversions from real to integer values the numbers with decimals will be rounded. If the user wishes to truncate the values, the CalcImg application can be used. In all cases, compression, decompression or change of format, the result may be a new raster file or overwritten on the original raster file.
The program is able to work with multiband raster files and, in this case, conversions can be performed on all bands simultaneously or on just one of the bands. When applied to all bands simultaneously the result can be a new raster or overwritten on the original.
The result of converting only a single band of a multiband image can be a new single band raster or alternatively it can be a new band added to the original multiband raster or it can be overwritten on the selected band of the original raster file.
It is also possible that one or other of the bands of a multiband raster file could be in the JPG raster format in which case no format conversion will be performed on this JPG band, but the results of the conversions on the other IMG bands will also include this unconverted band.
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| IMGIMG dialog box |