1TIFFRGBAImage(3TIFF)                                      TIFFRGBAImage(3TIFF)
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NAME

6       TIFFRGBAImageOK, TIFFRGBAImageBegin, TIFFRGBAImageGet, TIFFRGBAImageEnd
7       - read and decode an image into a raster
8

SYNOPSIS

10       #include <tiffio.h>
11
12       typedef  unsigned  char  TIFFRGBValue;  typedef  struct  _TIFFRGBAImage
13       TIFFRGBAImage;
14
15       int TIFFRGBAImageOK(TIFF *tif, char emsg[1024])
16       int  TIFFRGBAImageBegin(TIFFRGBAImage *img, TIFF* tif, int stopOnError,
17       char emsg[1024])
18       int TIFFRGBAImageGet(TIFFRGBAImage  *img,  uint32_t*  raster,  uint32_t
19       width , uint32_t height)
20       void TIFFRGBAImageEnd(TIFFRGBAImage *img)
21

DESCRIPTION

23       The  routines  described  here  provide  a high-level interface through
24       which TIFF images may be read into memory.  Images  may  be  strip-  or
25       tile-based  and  have a variety of different characteristics: bits/sam‐
26       ple, samples/pixel, photometric, etc.  Decoding state  is  encapsulated
27       in  a  TIFFRGBAImage  structure making it possible to capture state for
28       multiple images and quickly switch between  them.   The  target  raster
29       format  can  be  customized  to a particular application's needs by in‐
30       stalling custom routines that manipulate image data according to appli‐
31       cation requirements.
32
33       The  default usage for these routines is: check if an image can be pro‐
34       cessed using TIFFRGBAImageOK, construct a  decoder  state  block  using
35       TIFFRGBAImageBegin, read and decode an image into a target raster using
36       TIFFRGBAImageGet, and then release  resources  using  TIFFRGBAImageEnd.
37       TIFFRGBAImageGet  can be called multiple times to decode an image using
38       different state parameters.  If multiple images are to be displayed and
39       there  is  not  enough  space for each of the decoded rasters, multiple
40       state blocks can be managed and then calls can be made  to  TIFFRGBAIm‐
41       ageGet as needed to display an image.
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43       The  generated  raster  is assumed to be an array of width times height
44       32-bit entries, where width must be less than or equal to the width  of
45       the  image (height may be any non-zero size).  If the raster dimensions
46       are smaller than the image, the image data is  cropped  to  the  raster
47       bounds.   If  the raster height is greater than that of the image, then
48       the image data are placed in the lower part of the raster.  (Note  that
49       the  raster  is  assume to be organized such that the pixel at location
50       (x,y) is raster[y*width+x]; with the raster origin  in  the  lower-left
51       hand corner.)
52
53       Raster  pixels  are  8-bit packed red, green, blue, alpha samples.  The
54       macros TIFFGetR, TIFFGetG, TIFFGetB, and TIFFGetA should be used to ac‐
55       cess  individual  samples.  Images without Associated Alpha matting in‐
56       formation have a constant Alpha of 1.0 (255).
57
58       TIFFRGBAImageGet converts non-8-bit images by  scaling  sample  values.
59       Palette,  grayscale,  bilevel,  CMYK, and YCbCr images are converted to
60       RGB transparently.  Raster pixels are returned uncorrected by any  col‐
61       orimetry information present in the directory.
62
63       The  parameter  stopOnError specifies how to act if an error is encoun‐
64       tered while reading the image.  If stopOnError is non-zero, then an er‐
65       ror  will terminate the operation; otherwise TIFFRGBAImageGet will con‐
66       tinue processing data until all the possible data  in  the  image  have
67       been requested.
68

ALTERNATE RASTER FORMATS

70       To  use  the  core  support for reading and processing TIFF images, but
71       write the resulting raster data in a different  format  one  need  only
72       override  the ``put methods'' used to store raster data.  These methods
73       are are defined in the TIFFRGBAImage structure and initially  setup  by
74       TIFFRGBAImageBegin  to  point  to routines that pack raster data in the
75       default ABGR pixel format.  Two different routines are  used  according
76       to  the physical organization of the image data in the file: PlanarCon‐
77       figuration=1 (packed  samples),  and  PlanarConfiguration=2  (separated
78       samples).   Note  that this mechanism can be used to transform the data
79       before storing it in the raster.  For example one can convert  data  to
80       colormap indices for display on a colormap display.
81

SIMULTANEOUS RASTER STORE AND DISPLAY

83       It  is  simple  to  display an image as it is being read into memory by
84       overriding the put methods as described above for supporting  alternate
85       raster  formats.   Simply  keep  a reference to the default put methods
86       setup by TIFFRGBAImageBegin and then invoke them before or  after  each
87       display operation.  For example, the tiffgt(1) utility uses the follow‐
88       ing put method to update the display as the raster is being filled:
89
90       static void
91       putContigAndDraw(TIFFRGBAImage* img, uint32_t* raster,
92           uint32_t x, uint32_t y, uint32_t w, uint32_t h,
93           int32_t fromskew, int32_t toskew,
94           unsigned char* cp)
95       {
96           (*putContig)(img, raster, x, y, w, h, fromskew, toskew, cp);
97           if (x+w == width) {
98            w = width;
99            if (img->orientation == ORIENTATION_TOPLEFT)
100                lrectwrite(0, y-(h-1), w-1, y, raster-x-(h-1)*w);
101            else
102                lrectwrite(0, y, w-1, y+h-1, raster);
103           }
104       }
105
106       (the original routine provided by the library is saved in the  variable
107       putContig.)
108

SUPPORTING ADDITIONAL TIFF FORMATS

110       The  TIFFRGBAImage  routines support the most commonly encountered fla‐
111       vors of TIFF.  It is possible to extend this support by overriding  the
112       ``get  method''  invoked  by  TIFFRGBAImageGet to read TIFF image data.
113       Details of doing this are a bit involved, it is best to make a copy  of
114       an  existing  get method and modify it to suit the needs of an applica‐
115       tion.
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NOTES

118       Samples must be either 1, 2, 4,  8,  or  16  bits.   Colorimetric  sam‐
119       ples/pixel  must  be either 1, 3, or 4 (i.e.  SamplesPerPixel minus Ex‐
120       traSamples).
121
122       Palette image colormaps that appear to be incorrectly written as  8-bit
123       values are automatically scaled to 16-bits.
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RETURN VALUES

126       All routines return 1 if the operation was successful.  Otherwise, 0 is
127       returned if an error was encountered and stopOnError is zero.
128

DIAGNOSTICS

130       All error messages are directed to the TIFFError(3TIFF) routine.
131
132       Sorry, can not handle %d-bit pictures.   The  image  had  BitsPerSample
133       other than 1, 2, 4, 8, or 16.
134
135       Sorry, can not handle %d-channel images.  The image had SamplesPerPixel
136       other than 1, 3, or 4.
137
138       Missing needed "PhotometricInterpretation" tag.  The image did not have
139       a tag that describes how to display the data.
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141       No  "PhotometricInterpretation" tag, assuming RGB.  The image was miss‐
142       ing a tag that describes how to display it, but because it has 3  or  4
143       samples/pixel, it is assumed to be RGB.
144
145       No  "PhotometricInterpretation"  tag, assuming min-is-black.  The image
146       was missing a tag that describes how to display it, but because it  has
147       1 sample/pixel, it is assumed to be a grayscale or bilevel image.
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149       No space for photometric conversion table.  There was insufficient mem‐
150       ory for a table used to convert image samples to 8-bit RGB.
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152       Missing required "Colormap" tag.  A Palette image did not  have  a  re‐
153       quired Colormap tag.
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155       No space for tile buffer.  There was insufficient memory to allocate an
156       i/o buffer.
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158       No space for strip buffer.  There was insufficient memory  to  allocate
159       an i/o buffer.
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161       Can not handle format.  The image has a format (combination of BitsPer‐
162       Sample, SamplesPerPixel, and PhotometricInterpretation) that can not be
163       handled.
164
165       No space for B&W mapping table.  There was insufficient memory to allo‐
166       cate a table used to map grayscale data to RGB.
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168       No space for Palette mapping table.  There was insufficient  memory  to
169       allocate a table used to map data to 8-bit RGB.
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SEE ALSO

172       TIFFOpen(3TIFF),     TIFFReadRGBAImage(3TIFF),    TIFFReadRGBAImageOri‐
173       ented(3TIFF),    TIFFReadRGBAStrip(3TIFF),     TIFFReadRGBATile(3TIFF),
174       libtiff(3TIFF)
175
176       Libtiff library home page: http://www.simplesystems.org/libtiff/
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180libtiff                        October 29, 2004           TIFFRGBAImage(3TIFF)
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