Custom image format examples

Example 1: Lumisys X-ray scanner - creates 12 bit unpacked grayscale images with a fixed 2048-byte header, and stores data in big-endian format. No sample image file is needed.

1. Select ``File...Create file format''.
2. Set the following settings in the dialog box:

   
   

   Target platform	Mac
   Bit packing	None
   Format Identification	By Extension
   Compression	Off
   Identifier	lum
   Bytes to skip	2048
   Use header	(not checked)
   Header file	(leave blank)
   Header bytes	0
   Default bits/pixel	16
   Default Color type	Grayscale
   Default x size	128
   Default y size	128
   Default RGB bits/pixel	0 0 0
   Default black bits/pixel	0
   Default no. of frames	1
   Compression command	(leave blank)
   Compression extension	(leave blank)
   Decompression command	(leave blank)

   
   

3. Set the following file offsets:

   x size	806
   y size	808
   Bits/pixel	810
   All others	65535

4. Then click on ``OK''. The new file format will be created.
5. Reading and creating images in the new format will now occur transparently.

``Bytes to skip'' must be a multiple of 2 in this case, because there are 2 bytes (16 bits) per pixel. Skipping an odd number of bytes will cause the image will look strange because the light and dark areas are partially reversed.

Similarly, if the wrong target platform is selected, the image could look posterized or grainy, because the bytes are being put into the wrong pixels.

Here is the resulting $HOME/.tnimage/formats/lum file:

          # Format descriptor for lum image format
          # Created by tnimage 2.7.0 on Jun 24 1998
          identifier lum
          headerfile
          compression
          decompression
          compression_extension
          platform 20
          packing 0
          useheader 0
          useidentifier 0
          headerbytes 0
          skipbytes 2048
          compressflag 0
          defaultbpp 8
          defaultcolortype 0
          defaultxsize 128
          defaultysize 128
          defaultrbpp 0
          defaultgbpp 0
          defaultbbpp 0
          defaultkbpp 0
          defaultframes 1
          # Offsets into the uncompressed file:
          identifieroff 65535
          xoff 806
          yoff 808
          bppoff 810
          colortypeoff 65535
          compressflagoff 65535
          redbppoff 65535
          greenbppoff 65535
          bluebppoff 65535
          blackbppoff 65535
          xposoff 65535
          yposoff 65535
          framesoff 65535
          fpsoff 65535
          chromakeyoff 65535
          chromakey_graymin_off 65535
          chromakey_graymax_off 65535
          chromakey_rgbmin_off 65535
          chromakey_rgbmax_off 65535
          paletteoff 65535
          imageoff 65535

IMPORTANT: offsets must be set to 65535 unless they are definitely known to be in the image file.

Offsets are not arbitrary locations, and must correspond to the exact position in the file at which the parameter is located. Even when you are creating a new file format, some care must be taken to ensure that offsets do not overlap with each other or with image data. For an existing image in an unknown image format, it is often necessary to find an image of a known size and examine the image file with a hex editor to find out the locations at which the parameters are stored.

If an offset is set to 65535, it will be ignored and a default value will be used instead. Some of these default values are included in the format descriptor file. For example, if bppoff is set to 65535, the value in defaultbpp will be used. If bppoff is any other value, defaultbpp will be ignored and the value will be read from the image at the specified offset.

Example 2: Creating an IMDS file. IMDS is a little-known and rarely used monochrome format similar to GEM's IMG format, except that IMDS was used on IBM mainframes running MVS, and there seems to be no documentation for it.

1. Select ``File...Create file format''.
2. Set the following settings in the dialog box:

   
   

   Target platform	MVS
   Bit packing	TIF-like
   Format Identification	By Extension
   Extension	IMG
   Identifier	(none)
   Bytes to skip	0
   Use header	$\sqrt{}$(checked)
   Header file	(Name of a sample IMDS file)
   Header bytes	32
   Default bits/pixel	1
   Default No.of colors	1

   
   

3. Set the following file offsets:

   x size	12
   y size	14
   All others	65535

   
   

4. Then click on ``OK''. The new file format has been created.
5. Click on an image, or select something on the screen, and save it in the new IMG format (by clicking on ``Format'' then the last ``IMG'' item. The sample IMDS file must always be present to create image files in this format.
6. Test to make sure the image is readable. Since tnimage can already read this format, simply select ``File...Read'' and press Enter .

The default bits/pixel and default no.of colors are needed only if the these values are not in the header.

Example 3: Define a file format for multi-frame (3D) images.

• Select ``File...Create file format''.
• Set the following settings in the dialog box:

  Target platform	PC
  Bit packing	None
  Format Identification	By Identifier
  Compression	On
  Identifier	3d
  Bytes to skip	0
  Use header	(unchecked)
  Header file	(none)
  Header bytes	0
  Default bits/pixel	8
  Default color type	Indexed
  Default x size	128
  Default y size	128
  Default RGB bpp	0 0 0
  Default black bpp	0
  Default no. of frames	1
  Compression command	gzip -f
  Compression extension	.gz
  Decompression command	gunzip -c

  
  

  identifier offset	0
  x offset	4
  y offset	8
  bpp offset	12
  colortype offset	16
  compressflag offset	20
  redbpp offset	24
  greenbpp offset	28
  bluebpp offset	32
  blackbpp offset	36
  xpos offset	40
  ypos offset	44
  frames offset	48
  fps offset	52
  chromakey offset	56
  chr.gray min offset	60
  chr.gray max offset	64
  chr. RGB min offset	68
  chr. RGB max offset	72
  palette offset	76
  image offset	844

• Then click on ``OK''. The new file format has been created.

Here is the resulting $HOME/.tnimage/formats/3d file:

         # Format descriptor for 3d image format
         # Created by ./tnimage 2.7.0 on Jun 24 1998
         identifier 3d
         headerfile
         compression gzip -f
         decompression gunzip -c
         compression_extension .gz
         platform 21
         packing 1
         useheader 0
         useidentifier 1
         headerbytes 0
         skipbytes 0
         compressflag 1
         defaultbpp 8
         defaultcolortype 0
         defaultxsize 128
         defaultysize 128
         defaultrbpp 0
         defaultgbpp 0
         defaultbbpp 0
         defaultkbpp 0
         defaultframes 1
         # Offsets into the uncompressed file:
         identifieroff 0
         xoff 4
         yoff 8
         bppoff 12
         colortypeoff 16
         compressflagoff 20
         redbppoff 24
         greenbppoff 28
         bluebppoff 32
         blackbppoff 36
         xposoff 40
         yposoff 44
         framesoff 48
         fpsoff 52
         chromakeyoff 56
         chromakey_graymin_off 60
         chromakey_graymax_off 64
         chromakey_rgbmin_off 68
         chromakey_rgbmax_off 72
         paletteoff 76
         imageoff 844

Close image Removes the currently-selected image from the screen and frees up its memory. Also erases the image's backup and its FFT if present.

DOS Command Shell to DOS to execute a command or run a different program. Or, to obtain a DOS command line, enter Command. Type Exit to return to tnimage. DOS requires a small amount of memory below 1 megabyte to exit commands. Thus an ``insufficient memory'' error could occur even if there is a lot of high memory.

This function is, of course, not available in the Unix version.

Quit

Return to operating system. Alt-X also can be used to quit.