Alien-FreeImage
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src/Source/LibPNG/example.c view on Meta::CPAN
*/
/* This is an example of how to use libpng to read and write PNG files.
* The file libpng-manual.txt is much more verbose then this. If you have not
* read it, do so first. This was designed to be a starting point of an
* implementation. This is not officially part of libpng, is hereby placed
* in the public domain, and therefore does not require a copyright notice.
*
* This file does not currently compile, because it is missing certain
* parts, like allocating memory to hold an image. You will have to
* supply these parts to get it to compile. For an example of a minimal
* working PNG reader/writer, see pngtest.c, included in this distribution;
* see also the programs in the contrib directory.
*/
/* The simple, but restricted, approach to reading a PNG file or data stream
* just requires two function calls, as in the following complete program.
* Writing a file just needs one function call, so long as the data has an
* appropriate layout.
*
* The following code reads PNG image data from a file and writes it, in a
* potentially new format, to a new file. While this code will compile there is
* minimal (insufficient) error checking; for a more realistic version look at
* contrib/examples/pngtopng.c
*/
#include <stddef.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <png.h>
#include <zlib.h>
int main(int argc, const char **argv)
{
if (argc == 3)
{
png_image image; /* The control structure used by libpng */
/* Initialize the 'png_image' structure. */
memset(&image, 0, (sizeof image));
image.version = PNG_IMAGE_VERSION;
/* The first argument is the file to read: */
if (png_image_begin_read_from_file(&image, argv[1]) != 0)
{
png_bytep buffer;
/* Set the format in which to read the PNG file; this code chooses a
* simple sRGB format with a non-associated alpha channel, adequate to
* store most images.
*/
image.format = PNG_FORMAT_RGBA;
/* Now allocate enough memory to hold the image in this format; the
* PNG_IMAGE_SIZE macro uses the information about the image (width,
* height and format) stored in 'image'.
*/
buffer = malloc(PNG_IMAGE_SIZE(image));
/* If enough memory was available read the image in the desired format
* then write the result out to the new file. 'background' is not
* necessary when reading the image because the alpha channel is
* preserved; if it were to be removed, for example if we requested
* PNG_FORMAT_RGB, then either a solid background color would have to
* be supplied or the output buffer would have to be initialized to the
* actual background of the image.
*
* The fourth argument to png_image_finish_read is the 'row_stride' -
* this is the number of components allocated for the image in each
* row. It has to be at least as big as the value returned by
* PNG_IMAGE_ROW_STRIDE, but if you just allocate space for the
* default, minimum, size using PNG_IMAGE_SIZE as above you can pass
* zero.
*
* The final argument is a pointer to a buffer for the colormap;
* colormaps have exactly the same format as a row of image pixels (so
* you choose what format to make the colormap by setting
* image.format). A colormap is only returned if
* PNG_FORMAT_FLAG_COLORMAP is also set in image.format, so in this
* case NULL is passed as the final argument. If you do want to force
* all images into an index/color-mapped format then you can use:
*
* PNG_IMAGE_COLORMAP_SIZE(image)
*
* to find the maximum size of the colormap in bytes.
*/
if (buffer != NULL &&
png_image_finish_read(&image, NULL/*background*/, buffer,
0/*row_stride*/, NULL/*colormap*/) != 0)
{
/* Now write the image out to the second argument. In the write
* call 'convert_to_8bit' allows 16-bit data to be squashed down to
* 8 bits; this isn't necessary here because the original read was
* to the 8-bit format.
*/
if (png_image_write_to_file(&image, argv[2], 0/*convert_to_8bit*/,
buffer, 0/*row_stride*/, NULL/*colormap*/) != 0)
{
/* The image has been written successfully. */
exit(0);
}
}
else
{
/* Calling png_free_image is optional unless the simplified API was
* not run to completion. In this case if there wasn't enough
* memory for 'buffer' we didn't complete the read, so we must free
* the image:
*/
if (buffer == NULL)
png_free_image(&image);
else
free(buffer);
}
/* Something went wrong reading or writing the image. libpng stores a
* textual message in the 'png_image' structure:
*/
fprintf(stderr, "pngtopng: error: %s\n", image.message);
exit (1);
}
fprintf(stderr, "pngtopng: usage: pngtopng input-file output-file\n");
exit(1);
}
/* That's it ;-) Of course you probably want to do more with PNG files than
* just converting them all to 32-bit RGBA PNG files; you can do that between
* the call to png_image_finish_read and png_image_write_to_file. You can also
* ask for the image data to be presented in a number of different formats. You
* do this by simply changing the 'format' parameter set before allocating the
* buffer.
*
* The format parameter consists of five flags that define various aspects of
* the image, you can simply add these together to get the format or you can use
* one of the predefined macros from png.h (as above):
*
* PNG_FORMAT_FLAG_COLOR: if set the image will have three color components per
* pixel (red, green and blue), if not set the image will just have one
* luminance (grayscale) component.
*
* PNG_FORMAT_FLAG_ALPHA: if set each pixel in the image will have an additional
* alpha value; a linear value that describes the degree the image pixel
* covers (overwrites) the contents of the existing pixel on the display.
*
* PNG_FORMAT_FLAG_LINEAR: if set the components of each pixel will be returned
src/Source/LibPNG/example.c view on Meta::CPAN
/* Create and initialize the png_struct with the desired error handler
* functions. If you want to use the default stderr and longjump method,
* you can supply NULL for the last three parameters. We also supply the
* the compiler header file version, so that we know if the application
* was compiled with a compatible version of the library. REQUIRED
*/
png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING,
png_voidp user_error_ptr, user_error_fn, user_warning_fn);
if (png_ptr == NULL)
{
fclose(fp);
return (ERROR);
}
/* Allocate/initialize the memory for image information. REQUIRED. */
info_ptr = png_create_info_struct(png_ptr);
if (info_ptr == NULL)
{
fclose(fp);
png_destroy_read_struct(&png_ptr, NULL, NULL);
return (ERROR);
}
/* Set error handling if you are using the setjmp/longjmp method (this is
* the normal method of doing things with libpng). REQUIRED unless you
* set up your own error handlers in the png_create_read_struct() earlier.
*/
if (setjmp(png_jmpbuf(png_ptr)))
{
/* Free all of the memory associated with the png_ptr and info_ptr */
png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
fclose(fp);
/* If we get here, we had a problem reading the file */
return (ERROR);
}
/* One of the following I/O initialization methods is REQUIRED */
#ifdef streams /* PNG file I/O method 1 */
/* Set up the input control if you are using standard C streams */
png_init_io(png_ptr, fp);
#else no_streams /* PNG file I/O method 2 */
/* If you are using replacement read functions, instead of calling
* png_init_io() here you would call:
*/
png_set_read_fn(png_ptr, (void *)user_io_ptr, user_read_fn);
/* where user_io_ptr is a structure you want available to the callbacks */
#endif no_streams /* Use only one I/O method! */
/* If we have already read some of the signature */
png_set_sig_bytes(png_ptr, sig_read);
#ifdef hilevel
/*
* If you have enough memory to read in the entire image at once,
* and you need to specify only transforms that can be controlled
* with one of the PNG_TRANSFORM_* bits (this presently excludes
* quantizing, filling, setting background, and doing gamma
* adjustment), then you can read the entire image (including
* pixels) into the info structure with this call:
*/
png_read_png(png_ptr, info_ptr, png_transforms, NULL);
#else
/* OK, you're doing it the hard way, with the lower-level functions */
/* The call to png_read_info() gives us all of the information from the
* PNG file before the first IDAT (image data chunk). REQUIRED
*/
png_read_info(png_ptr, info_ptr);
png_get_IHDR(png_ptr, info_ptr, &width, &height, &bit_depth, &color_type,
&interlace_type, NULL, NULL);
/* Set up the data transformations you want. Note that these are all
* optional. Only call them if you want/need them. Many of the
* transformations only work on specific types of images, and many
* are mutually exclusive.
*/
/* Tell libpng to strip 16 bit/color files down to 8 bits/color.
* Use accurate scaling if it's available, otherwise just chop off the
* low byte.
*/
#ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED
png_set_scale_16(png_ptr);
#else
png_set_strip_16(png_ptr);
#endif
/* Strip alpha bytes from the input data without combining with the
* background (not recommended).
*/
png_set_strip_alpha(png_ptr);
/* Extract multiple pixels with bit depths of 1, 2, and 4 from a single
* byte into separate bytes (useful for paletted and grayscale images).
*/
png_set_packing(png_ptr);
/* Change the order of packed pixels to least significant bit first
* (not useful if you are using png_set_packing). */
png_set_packswap(png_ptr);
/* Expand paletted colors into true RGB triplets */
if (color_type == PNG_COLOR_TYPE_PALETTE)
png_set_palette_to_rgb(png_ptr);
/* Expand grayscale images to the full 8 bits from 1, 2, or 4 bits/pixel */
if (color_type == PNG_COLOR_TYPE_GRAY && bit_depth < 8)
png_set_expand_gray_1_2_4_to_8(png_ptr);
/* Expand paletted or RGB images with transparency to full alpha channels
* so the data will be available as RGBA quartets.
*/
if (png_get_valid(png_ptr, info_ptr, PNG_INFO_tRNS) != 0)
png_set_tRNS_to_alpha(png_ptr);
/* Set the background color to draw transparent and alpha images over.
* It is possible to set the red, green, and blue components directly
* for paletted images instead of supplying a palette index. Note that
* even if the PNG file supplies a background, you are not required to
* use it - you should use the (solid) application background if it has one.
*/
png_color_16 my_background, *image_background;
if (png_get_bKGD(png_ptr, info_ptr, &image_background) != 0)
png_set_background(png_ptr, image_background,
PNG_BACKGROUND_GAMMA_FILE, 1, 1.0);
else
png_set_background(png_ptr, &my_background,
PNG_BACKGROUND_GAMMA_SCREEN, 0, 1.0);
/* Some suggestions as to how to get a screen gamma value
*
* Note that screen gamma is the display_exponent, which includes
* the CRT_exponent and any correction for viewing conditions
*/
if (/* We have a user-defined screen gamma value */)
{
screen_gamma = user-defined screen_gamma;
}
/* This is one way that applications share the same screen gamma value */
else if ((gamma_str = getenv("SCREEN_GAMMA")) != NULL)
{
screen_gamma = atof(gamma_str);
}
/* If we don't have another value */
else
{
screen_gamma = PNG_DEFAULT_sRGB; /* A good guess for a PC monitor
in a dimly lit room */
screen_gamma = PNG_GAMMA_MAC_18 or 1.0; /* Good guesses for Mac systems */
}
/* Tell libpng to handle the gamma conversion for you. The final call
* is a good guess for PC generated images, but it should be configurable
* by the user at run time by the user. It is strongly suggested that
* your application support gamma correction.
*/
int intent;
if (png_get_sRGB(png_ptr, info_ptr, &intent) != 0)
png_set_gamma(png_ptr, screen_gamma, PNG_DEFAULT_sRGB);
else
{
double image_gamma;
if (png_get_gAMA(png_ptr, info_ptr, &image_gamma) != 0)
png_set_gamma(png_ptr, screen_gamma, image_gamma);
else
png_set_gamma(png_ptr, screen_gamma, 0.45455);
}
#ifdef PNG_READ_QUANTIZE_SUPPORTED
/* Quantize RGB files down to 8 bit palette or reduce palettes
* to the number of colors available on your screen.
*/
if ((color_type & PNG_COLOR_MASK_COLOR) != 0)
{
int num_palette;
png_colorp palette;
/* This reduces the image to the application supplied palette */
if (/* We have our own palette */)
{
/* An array of colors to which the image should be quantized */
png_color std_color_cube[MAX_SCREEN_COLORS];
png_set_quantize(png_ptr, std_color_cube, MAX_SCREEN_COLORS,
MAX_SCREEN_COLORS, NULL, 0);
}
/* This reduces the image to the palette supplied in the file */
else if (png_get_PLTE(png_ptr, info_ptr, &palette, &num_palette) != 0)
{
png_uint_16p histogram = NULL;
png_get_hIST(png_ptr, info_ptr, &histogram);
png_set_quantize(png_ptr, palette, num_palette,
max_screen_colors, histogram, 0);
}
}
#endif /* READ_QUANTIZE */
/* Invert monochrome files to have 0 as white and 1 as black */
png_set_invert_mono(png_ptr);
/* If you want to shift the pixel values from the range [0,255] or
* [0,65535] to the original [0,7] or [0,31], or whatever range the
* colors were originally in:
*/
if (png_get_valid(png_ptr, info_ptr, PNG_INFO_sBIT) != 0)
{
png_color_8p sig_bit_p;
png_get_sBIT(png_ptr, info_ptr, &sig_bit_p);
png_set_shift(png_ptr, sig_bit_p);
}
/* Flip the RGB pixels to BGR (or RGBA to BGRA) */
if ((color_type & PNG_COLOR_MASK_COLOR) != 0)
png_set_bgr(png_ptr);
/* Swap the RGBA or GA data to ARGB or AG (or BGRA to ABGR) */
png_set_swap_alpha(png_ptr);
/* Swap bytes of 16 bit files to least significant byte first */
png_set_swap(png_ptr);
/* Add filler (or alpha) byte (before/after each RGB triplet) */
png_set_filler(png_ptr, 0xff, PNG_FILLER_AFTER);
#ifdef PNG_READ_INTERLACING_SUPPORTED
/* Turn on interlace handling. REQUIRED if you are not using
* png_read_image(). To see how to handle interlacing passes,
* see the png_read_row() method below:
*/
number_passes = png_set_interlace_handling(png_ptr);
#else
number_passes = 1;
#endif /* READ_INTERLACING */
/* Optional call to gamma correct and add the background to the palette
* and update info structure. REQUIRED if you are expecting libpng to
* update the palette for you (ie you selected such a transform above).
*/
png_read_update_info(png_ptr, info_ptr);
/* Allocate the memory to hold the image using the fields of info_ptr. */
/* The easiest way to read the image: */
png_bytep row_pointers[height];
/* Clear the pointer array */
for (row = 0; row < height; row++)
row_pointers[row] = NULL;
for (row = 0; row < height; row++)
row_pointers[row] = png_malloc(png_ptr, png_get_rowbytes(png_ptr,
info_ptr));
/* Now it's time to read the image. One of these methods is REQUIRED */
#ifdef entire /* Read the entire image in one go */
png_read_image(png_ptr, row_pointers);
#else no_entire /* Read the image one or more scanlines at a time */
/* The other way to read images - deal with interlacing: */
for (pass = 0; pass < number_passes; pass++)
{
#ifdef single /* Read the image a single row at a time */
for (y = 0; y < height; y++)
{
png_read_rows(png_ptr, &row_pointers[y], NULL, 1);
}
#else no_single /* Read the image several rows at a time */
for (y = 0; y < height; y += number_of_rows)
{
#ifdef sparkle /* Read the image using the "sparkle" effect. */
png_read_rows(png_ptr, &row_pointers[y], NULL,
number_of_rows);
#else no_sparkle /* Read the image using the "rectangle" effect */
png_read_rows(png_ptr, NULL, &row_pointers[y],
number_of_rows);
#endif no_sparkle /* Use only one of these two methods */
}
/* If you want to display the image after every pass, do so here */
#endif no_single /* Use only one of these two methods */
}
#endif no_entire /* Use only one of these two methods */
/* Read rest of file, and get additional chunks in info_ptr - REQUIRED */
png_read_end(png_ptr, info_ptr);
#endif hilevel
/* At this point you have read the entire image */
/* Clean up after the read, and free any memory allocated - REQUIRED */
png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
/* Close the file */
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