png_read SYNOPSIS Read an image from a PNG file USAGE img = png_read (file [,&image_type]) DESCRIPTION The `png_read' function reads the image from the specified file and returns it. If a second argument is present, then it must be a reference to a variable that will be set to an integer representing the type of image read: PNG_COLOR_TYPE_RGB (RGB image) PNG_COLOR_TYPE_RGBA (RGB image with an alpha channel) PNG_COLOR_TYPE_GRAY (Grayscale image) PNG_COLOR_TYPE_GRAY_ALPHA (Grayscale image with an alpha channel) The image returned by this function is represented by a 2d array of unsigned integers. If the image type is `PNG_COLOR_TYPE_RGB' or `PNG_COLOR_TYPE_RGBA', then the integers will be 32 bits wide with the most significant byte corresponding to the alpha channel, followed by bytes for the red, green, and blue channels in that order. In this way, the color channels may be extracted from the image through simple bit operations, e.g., (img & 0x0000FF00) shr 8 will pick out the green channel. Alternatively, the `png_rgb_get_?' functions may be used to extract the various channels. If the image type is `PNG_COLOR_TYPE_GRAY_ALPHA' then image will be represented by 16 bit integers with the most significant byte corresponding to the alpha channel and the least significant byte representing the grayscale. If the image type is `PNG_COLOR_TYPE_GRAY' then the image array will consist of unsigned 8 bit integers (`UChar_Type'). EXAMPLE define read_grayscale_image (file) { variable img_type; img = png_read (file, &img_type); if ((img_type != PNG_COLOR_TYPE_GRAY) or (img_type != PNG_COLOR_TYPE_GRAY_ALPHA)) img = png_rgb_to_gray (img); return img; } SEE ALSO png_read_flipped, png_write, png_rgb_to_r, png_rgb_to_g, png_rgb_to_b -------------------------------------------------------------- png_read_flipped SYNOPSIS Read an image from a PNG file USAGE img = png_read_flipped (file [,&image_type]) DESCRIPTION This function is like the `png_read' function except that it returns an image with the rows flipped. See the documentation for `png_read' for more information. SEE ALSO png_read, png_write_flipped -------------------------------------------------------------- png_write SYNOPSIS Write an image to a PNG file USAGE png_write (file, image [,has_alpha]) DESCRIPTION The `png_write' function writes a 2d image to the specified file as a PNG. The type of PNG created depends upon the data type of the image array according to the following table: data-type PNG-type ----------------------------------- Char_Type (8 bit) grayscale UChar_Type (8 bit) grayscale Int16_Type (16 bit) grayscale UInt16_Type (16 bit) grayscale Int32_Type (32 bit) RGB UInt32_Type (32 bit) RGB If the optional parameter `has_alpha' is present and non-zero, then an alpha channel will also be written to the file. See the documentation for the `png_read' function for information about how the various channels are encoded as integers. SEE ALSO png_write_flipped, png_read -------------------------------------------------------------- png_write_flipped SYNOPSIS Write an image to a PNG file USAGE png_write_flipped (file, image [,has_alpha]) DESCRIPTION This function is like the `png_write' function except that it writes the image to the file with the rows reversed. See the documentation for `png_write' for more information. SEE ALSO png_read, png_write_flipped -------------------------------------------------------------- png_rgb_to_gray SYNOPSIS Convert an RGB image to grayscale USAGE gray = png_rgb_to_gray (rgb) DESCRIPTION This function converts an RGB image represented by an array (typically 2d) to a corresponding array of 8 bit integers representing the grayscale values. The grayscale values are formed by averaging the R, G, and B channels. SEE ALSO png_gray_to_rgb -------------------------------------------------------------- png_gray_to_rgb SYNOPSIS Convert a grayscale image to RGB USAGE rgb = png_gray_to_rgb (gray, colormap) DESCRIPTION This function creates an RGB image, represented by an array of 32 bit integers from a grayscale image using the specified colormap. The shape of the of the RGB array will be that of the input grayscale array. The values in the input image will be linearly mapped onto the elements of the colormap such that the minimum value in the grayscale image will be assigned the first RGB value in the colormap, and the maximum value will be assigned the last RGB value. The colormap argument must either be an array of 32 bit integers encoding the RGB information, or must be the name of a supported color map. See the documentation for the `png_get_colormap' function for more information about colormaps. QUALIFIERS The qualifiers `gmin' and `gmax' may be used to define the minimum and maximum grayscale values used for the mapping onto the colormap. Grayscale values outside the specified range will be clipped. SEE ALSO png_rgb_to_gray, png_get_colormap -------------------------------------------------------------- png_get_colormap SYNOPSIS Retrieve a colormap USAGE cmap = png_get_colormap (String_Type name) DESCRIPTION This function returns a colormap of the specified name. Currently recognized names include: cool Linear change from blue to magenta copper Dark to light copper brown gebco Colors for GEBCO bathymetric charts globe Colors for global bathy-topo relief drywet Goes from dry to wet colors gray Grayramp from black to white haxby Bill Haxby's colortable for geoid & gravity hot Black through red and yellow to white jet Dark to light blue, white, yellow and red no_green For those who hate green ocean white-green-blue bathymetry scale polar Blue via white to red rainbow Rainbow colors magenta-blue-cyan-green-yellow-red red2green Polar scale from red to green via white relief Wessel/Martinez colortable for bathymetry/topography topo Sandwell-Anderson colors for topography sealand Smith bathymetry/topography scale seis R-O-Y-G-B seismic tomography colors split Polar scale like polar, but via black instead of white wysiwyg 20 RGB colors for openwin -cubesize large and waxenvy printer The above colormaps were derived from the GMT distribution, which is an open source collection of tools for geographic data. See `http://gmt.soest.hawaii.edu/' for more information about GMT. In the current implementation, the colormap is a 256 element array of unsigned 32 bit integers. SEE ALSO png_gray_to_rgb, png_add_colormap, png_get_colormap_names -------------------------------------------------------------- png_add_colormap SYNOPSIS Add a color map USAGE png_add_colormap (name, cmap) DESCRIPTION This function adds a color map of the specified name to the table of internal colormaps. The colormap is simply a 256 element unsigned 32 integer bit array that maps 256 grayscale values to RGB. SEE ALSO png_get_colormap -------------------------------------------------------------- png_get_r SYNOPSIS Get the red channel of an RGB image USAGE r = png_get_r (rgb) DESCRIPTION This function returns the red component of the RGB image encoded as an unsigned 32 bit integer using the algorithm: r = typecast ((rgb shr 16) & 0xFF, UChar_Type); SEE ALSO png_get_g, png_get_b, png_get_a -------------------------------------------------------------- png_get_g SYNOPSIS Get the green channel of an RGB image USAGE r = png_get_g (rgb) DESCRIPTION This function returns the green component of the RGB image encoded as an unsigned 32 bit integer using the algorithm: g = typecast ((rgb shr 8) & 0xFF, UChar_Type); SEE ALSO png_get_r, png_get_b, png_get_a -------------------------------------------------------------- png_get_b SYNOPSIS Get the blue channel of an RGB image USAGE r = png_get_b (rgb) DESCRIPTION This function returns the blue component of the RGB image encoded as an unsigned 32 bit integer using the algorithm: b = typecast ((rgb & 0xFF), UChar_Type); SEE ALSO png_get_r, png_get_g, png_get_a -------------------------------------------------------------- png_get_a SYNOPSIS Get the alpha channel of an RGB image USAGE r = png_get_a (rgb) DESCRIPTION This function returns the alpha channel of the RGB image encoded as an unsigned 32 bit integer using the algorithm: a = typecast ((rgb shr 24) & 0xFF, UChar_Type); SEE ALSO png_get_g, png_get_b, png_get_a --------------------------------------------------------------