Imager::interface(3) User Contributed Perl Documentation Imager::interface(3)NAME
Imager::interface.pod - describes the C level virtual image interface
SYNOPSISDESCRIPTION
The Imager virtual interface aims to allow image types to be created
for special purposes, both to allow consistent access to images with
different sample sizes, and organizations, but also to allow creation
of synthesized or virtual images.
This is a C level interface rather than Perl.
Existing Images
As of this writing we have the following concrete image types:
· 8-bit/sample direct images
· 16-bit/sample direct images
· double/sample direct images
· 8-bit/sample 8-bit/index paletted images
Currently there is only one virtual image type:
· masked images, where a mask image can control write access to an
underlying image.
Other possible concrete images include:
· "bitmaps", 1 bit/sample images (perhaps limited to a single
channel)
· 16-bit/index paletted images
Some other possible virtual images:
· image alpha combining, where the combining function can be
specified (see the layer modes in graphical editors like the GIMP
or Photoshop.
THE INTERFACE
Each image type needs to define a number of functions which implement
the image operations.
The image structure includes information describes the image, which can
be used to determine the structure of the image:
· "channels" - the number of samples kept for each pixel in the
image. For paletted images the samples are kept for each entry in
the palette.
· "xsize", "ysize" - the dimensions of the image in pixels.
· "bytes" - the number of bytes of data kept for the image. Zero for
virtual images. Does not include the space required for the
palette for paletted images.
· "ch_mask" - controls which samples will be written to for direct
images.
· "bits" - the number of bits kept for each sample. There are enum
values i_8_bits, i_16_bits and i_double_bits (64).
· "type" - the type of image, either i_direct_type or i_palette_type.
Direct images keep the samples for every pixel image, while
i_palette_type images keep an index into a color table for each
pixel.
· "virtual" - whether the image keeps any pixel data. If this is
non-zero then "idata" points to image data, otherwise it points to
implementation defined data, though "ext_data" is more likely to be
used for that.
· "idata" - image data. If the image is 8-bit direct, non-virtual,
then this consists of each sample of the image stored one after
another, otherwise it is implementation defined.
· "tags" - will be used to store meta-data for an image, eg. tags
from a TIFF file, or animation information from a GIF file. This
should be initialized with a call to i_tags_new() in your image
constructor if creating a new image type.
· "ext_data" - for internal use of image types. This is not released
by the standard i_img_exorcise() function. If you create a new
image type and want to store a pointer to allocated memory here you
should point i_f_destroy at a function that will release the data.
If a caller has no knowledge of the internal format of an image, the
caller must call the appropriate image function pointer. Imager
provides macros that wrap these functions, so it isn't necessary to
call them directly.
Many functions have a similar function with an 'f' suffix, these take
or return samples specified with floating point values rather than
8-bit integers (unsigned char). Floating point samples are returned in
the range 0 to 1 inclusive.
i_f_ppix(im,x,y,color)
i_f_ppixf(im,x,y,fcolor)
stores the specified color at pixel (x,y) in the image. If the
pixel can be stored return 0, otherwise -1. An image type may
choose to return 0 under some circumstances, eg. writing to a
masked area of an image. The "color" or "fcolor" always contains
the actual samples to be written, rather than a palette index.
i_f_plin(im,l,r,y,colors)
i_f_plinf(im,l,r,y,fcolors)
stores (r-l) pixels at positions (l,y) ... (r-1, y) from the array
specified by "colors" (or "fcolors"). Returns the number of pixels
written to. If l is negative it will return 0. If "r > im->xsize"
then only "(im->xsize - l)" will be written.
i_f_gpix(im,x,y,color)
i_f_gpixf(im,x,y,fcolor)
retrieves a single pixel from position (x,y). This returns the
samples rather than the index for paletted images.
i_f_glin(im,l,r,y,colors)
i_f_glinf(im,l,r,y,fcolors)
retrieves (r-l) pixels from positions (l, y) through (r-1, y) into
the array specified by colors. Returns the number of pixels
retrieved. If l < 0 no pixels are retrieved. If "r > im->xsize"
then pixels "(l, y)" ... "(im->xsize-1, y)" are retrieved.
Retrieves the samples rather than the color indexes for paletted
images.
i_f_gsamp(im,l,r,y,samples,chans,chan_count)
i_f_gsampf(im,l,r,y,fsamples,chans,chan_count)
Retrieves samples from channels specified by "chans" (for length
"chan_count") from pixels at positions (l,y) ... (r-1, y). If
"chans" is NULL then samples from channels 0 ... "chan_count-1"
will be retrieved. Returns the number of sample retrieved (not the
number of channels). If a channel in "chans" is not present in the
image or l < 0, returns 0. If "r > im->xsize", then the samples
from "(l,y)" ... "(im->xsize-1, y)" are returned.
The following are for images where type == i_palette_type only.
i_f_gpal(im,l,r,y,vals)
Retrieves color indexes from the image for pixels (l, y) ... (r-1,
y) into "vals". Returns the number of indexes retrieved.
i_f_ppal(im,l,r,y,vals)
Stores color indexes into the image for pixels (l, y) ... (r-1, y)
from "vals". Returns the number of indexes retrieved. If indexes
are outside the range of the images palette, then you may have
problems reading those pixels with i_gpix() or i_glin().
i_f_addcolors(im,colors,count)
Adds the count colors to the image's palette. Returns the index of
the first color added, or -1 if there is not enough space for count
colors.
i_f_getcolors(im,index,colors,count)
Retrieves count colors from the image's palette starting from entry
index in the palette. Returns non-zero on success.
i_f_colorcount(im)
Returns the number of colors in the image's palette. Returns -1 if
this is not a paletted image.
i_f_maxcolors(im)
Returns the maximum number of colors that can fit in the image's
palette. Returns -1 if this is not a paletted image.
i_f_findcolor(im,color,entry)
Searches the image's palette for the specified color, setting
*entry to the index and returning non-zero. Returns zero if the
color is not found.
i_f_setcolors_t(im,index,colors,count)
Sets count colors starting from index in the image from the array
colors. The colors to be set must already have entries in the
image's palette. Returns non-zero on success.
Finally, the i_f_destroy function pointer can be set which is called
when the image is destroyed. This can be used to release memory
pointed to by ext_data or release any other resources.
When writing to a paletted image with i_ppix() or i_plin() and the
color you are writing doesn't exist in the image, then it's possible
that the image will be internally converted to a direct image with the
same number of channels.
TOOLS
Several functions have been written to simplify creating new image
types.
These tools are available by including imagei.h.
Floating point wrappers
These functions implement the floating point sample versions of each
interface function in terms of the integer sample version.
These are:
i_ppixf_fp
i_gpixf_fp
i_plinf_fp
i_glinf_fp
i_gsampf_fp
Forwarding functions
These functions are used in virtual images where the call should simply
be forwarded to the underlying image. The underlying image is assumed
to be the first pointer in a structure pointed at by ext_data.
If this is not the case then these functions will just crash :)
i_addcolors_forward
i_getcolors_forward
i_colorcount_forward
i_maxcolors_forward
i_findcolor_forward
i_setcolors_forward
Sample macros
"Imagei.h" defines several macros for converting samples between
different sizes.
Each macro is of the form "Sample"size"To"size where size is one of 8,
16, or F (for floating-point samples).
SampleFTo16(sample)Sample16ToF(sample)SampleFTo8(sample)Sample8ToF(sample)Sample16To8(num)Sample8To16(num)perl v5.14.3 2012-09-28 Imager::interface(3)
