====== WriteImage ======
WriteImage writes the image it receives to a file, in one of six formats. The file name must end in the format's extension.

^ Format ^ Extension ^ Data it can hold ^ Best for ^
| TIFF | ''.tif'' | 8- or 16-bit integers, or 32- or 64-bit floating point | archiving |
| ENVI | ''.hdr'' | 8- or 16-bit integers, or 32- or 64-bit floating point | computations |
| JPEG | ''.jpg'' | 8-bit monochrome or color (1 or 3 bands) | display only |
| PNG | ''.png'' | 8-bit monochrome or color | |
| BMP | ''.bmp'' | 8-bit monochrome or color | |
| Text | ''.txt'' | a simple text format unique to Hoku | |

To write an image for display in other programs, first convert it to 8-bit with [[basic_level:enhancement:pack|Pack]].

WriteImage passes the image on unchanged, so you can connect another module after it. Each output file name can be used only once in a job.

===== JPEG =====
JPEG files use lossy compression. The "quality" parameter goes from 0.0 (lowest quality, smallest file) to 1.0 (highest quality, largest file). The default is 0.75.

{{ :basic_level:hoku_basic_writeimage_jpg.png?nolink&400 |WriteImage with the JPEG format}}

===== TIFF =====
TIFF files are written uncompressed by default. Two lossless compression options are available, LZW and Deflate. Both can be combined with **Differencing** (the "predictor") for more compression. Deflate with Differencing gives the best compression. LZW is provided for compatibility, but is not recommended.

{{ :basic_level:hoku_basic_writeimage_tiff.png?nolink&400 |WriteImage with the TIFF format and Deflate compression}}

===== ENVI =====
An ENVI file is a header file (''.hdr'') plus a data file. The "interleave" parameter sets how the data is written:
  * **BSQ** (band sequential, the default) is best when you want to look at one band at a time.
  * **BIP** (band interleaved by pixel) lets you look at all bands at once, as in a spectrum.
  * **BIL** (band interleaved by line) is a compromise in access speed.

{{ :basic_level:hoku_basic_writeimage_envi.png?nolink&400 |WriteImage with the ENVI format}}

For writing a multispectral image, see [[basic_level:writeimage:multispectral_image_in_envi|Multispectral Image in ENVI]].