/*====================================================================* - Copyright (C) 2001 Leptonica. All rights reserved. - - Redistribution and use in source and binary forms, with or without - modification, are permitted provided that the following conditions - are met: - 1. Redistributions of source code must retain the above copyright - notice, this list of conditions and the following disclaimer. - 2. Redistributions in binary form must reproduce the above - copyright notice, this list of conditions and the following - disclaimer in the documentation and/or other materials - provided with the distribution. - - THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS - ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT - LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR - A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL ANY - CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, - EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, - PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR - PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY - OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING - NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS - SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. *====================================================================*/ /* * pngio.c * * Read png from file * PIX *pixReadStreamPng() * l_int32 readHeaderPng() * l_int32 freadHeaderPng() * l_int32 sreadHeaderPng() * l_int32 fgetPngResolution() * * Write png to file * l_int32 pixWritePng() [ special top level ] * l_int32 pixWriteStreamPng() * l_int32 pixSetZlibCompression() * * Setting flag for special read mode * void l_pngSetReadStrip16To8() * * Read/write to memory * PIX *pixReadMemPng() * l_int32 pixWriteMemPng() * * Documentation: libpng.txt and example.c * * On input (decompression from file), palette color images * are read into an 8 bpp Pix with a colormap, and 24 bpp * 3 component color images are read into a 32 bpp Pix with * rgb samples. On output (compression to file), palette color * images are written as 8 bpp with the colormap, and 32 bpp * full color images are written compressed as a 24 bpp, * 3 component color image. * * In the following, we use these abbreviations: * bps == bit/sample * spp == samples/pixel * bpp == bits/pixel of image in Pix (memory) * where each component is referred to as a "sample". * * For reading and writing rgb and rgba images, we read and write * alpha if it exists (spp == 4) and do not read or write if * it doesn't (spp == 3). The alpha component can be 'removed' * simply by setting spp to 3. In leptonica, we make relatively * little explicit use of the alpha sample. Note that the alpha * sample in the image is also called "alpha transparency", * "alpha component" and "alpha layer." * * To change the zlib compression level, use pixSetZlibCompression() * before writing the file. The default is for standard png compression. * The zlib compression value can be set [0 ... 9], with * 0 no compression (huge files) * 1 fastest compression * -1 default compression (equivalent to 6 in latest version) * 9 best compression * Note that if you are using the defined constants in zlib instead * of the compression integers given above, you must include zlib.h. * * There is global for determining the size of retained samples: * var_PNG_STRIP_16_to_8 * and a function l_pngSetReadStrip16To8() for setting it. * The default is TRUE, which causes pixRead() to strip each 16 bit * sample down to 8 bps: * - For 16 bps rgb (16 bps, 3 spp) --> 32 bpp rgb Pix * - For 16 bps gray (16 bps, 1 spp) --> 8 bpp grayscale Pix * If the variable is set to FALSE, the 16 bit gray samples * are saved when read; the 16 bit rgb samples return an error. * Note: results can be non-deterministic if used with * multi-threaded applications. * * On systems like windows without fmemopen() and open_memstream(), * we write data to a temp file and read it back for operations * between pix and compressed-data, such as pixReadMemPng() and * pixWriteMemPng(). */ #include #include "allheaders.h" #ifdef HAVE_CONFIG_H #include "config_auto.h" #endif /* HAVE_CONFIG_H */ /* --------------------------------------------*/ #if HAVE_LIBPNG /* defined in environ.h */ /* --------------------------------------------*/ #include "png.h" #if HAVE_LIBZ #include "zlib.h" #else #define Z_DEFAULT_COMPRESSION (-1) #endif /* HAVE_LIBZ */ /* ------------------ Set default for read option -------------------- */ /* Strip 16 bpp --> 8 bpp on reading png; default is for stripping. * If you don't strip, you can't read the gray-alpha spp = 2 images. */ static l_int32 var_PNG_STRIP_16_TO_8 = 1; #ifndef NO_CONSOLE_IO #define DEBUG_READ 0 #define DEBUG_WRITE 0 #endif /* ~NO_CONSOLE_IO */ /*---------------------------------------------------------------------* * Reading png * *---------------------------------------------------------------------*/ /*! * pixReadStreamPng() * * Input: stream * Return: pix, or null on error * * Notes: * (1) If called from pixReadStream(), the stream is positioned * at the beginning of the file. * (2) To do sequential reads of png format images from a stream, * use pixReadStreamPng() * (3) Grayscale-with-alpha pngs (spp = 2) are converted to RGBA * on read; the returned pix has spp = 4 and equal red, green and * blue channels. * (4) spp = 1 with alpha (palette) is converted to RGBA with spp = 4. * (5) We use the high level png interface, where the transforms are set * up in advance and the header and image are read with a single * call. The more complicated interface, where the header is * read first and the buffers for the raster image are user- * allocated before reading the image, works OK for single images, * but I could not get it to work properly for the successive * png reads that are required by pixaReadStream(). */ PIX * pixReadStreamPng(FILE *fp) { l_int32 rval, gval, bval; l_int32 i, j, k, index, ncolors; l_int32 wpl, d, spp, cindex, tRNS; l_uint32 png_transforms; l_uint32 *data, *line, *ppixel; int num_palette, num_text, num_trans; png_byte bit_depth, color_type, channels; png_uint_32 w, h, rowbytes; png_uint_32 xres, yres; png_bytep rowptr, trans; png_bytep *row_pointers; png_structp png_ptr; png_infop info_ptr, end_info; png_colorp palette; png_textp text_ptr; /* ptr to text_chunk */ PIX *pix; PIXCMAP *cmap; PROCNAME("pixReadStreamPng"); if (!fp) return (PIX *)ERROR_PTR("fp not defined", procName, NULL); pix = NULL; /* Allocate the 3 data structures */ if ((png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, (png_voidp)NULL, NULL, NULL)) == NULL) return (PIX *)ERROR_PTR("png_ptr not made", procName, NULL); if ((info_ptr = png_create_info_struct(png_ptr)) == NULL) { png_destroy_read_struct(&png_ptr, (png_infopp)NULL, (png_infopp)NULL); return (PIX *)ERROR_PTR("info_ptr not made", procName, NULL); } if ((end_info = png_create_info_struct(png_ptr)) == NULL) { png_destroy_read_struct(&png_ptr, &info_ptr, (png_infopp)NULL); return (PIX *)ERROR_PTR("end_info not made", procName, NULL); } /* Set up png setjmp error handling */ if (setjmp(png_jmpbuf(png_ptr))) { png_destroy_read_struct(&png_ptr, &info_ptr, &end_info); return (PIX *)ERROR_PTR("internal png error", procName, NULL); } png_init_io(png_ptr, fp); /* ---------------------------------------------------------- * * Set the transforms flags. Whatever happens here, * NEVER invert 1 bpp using PNG_TRANSFORM_INVERT_MONO. * ---------------------------------------------------------- */ /* To strip 16 --> 8 bit depth, use PNG_TRANSFORM_STRIP_16 */ if (var_PNG_STRIP_16_TO_8 == 1) /* our default */ png_transforms = PNG_TRANSFORM_STRIP_16; else png_transforms = PNG_TRANSFORM_IDENTITY; /* Read it */ png_read_png(png_ptr, info_ptr, png_transforms, NULL); row_pointers = png_get_rows(png_ptr, info_ptr); w = png_get_image_width(png_ptr, info_ptr); h = png_get_image_height(png_ptr, info_ptr); bit_depth = png_get_bit_depth(png_ptr, info_ptr); rowbytes = png_get_rowbytes(png_ptr, info_ptr); color_type = png_get_color_type(png_ptr, info_ptr); channels = png_get_channels(png_ptr, info_ptr); spp = channels; tRNS = png_get_valid(png_ptr, info_ptr, PNG_INFO_tRNS) ? 1 : 0; if (spp == 1) { d = bit_depth; } else { /* spp == 2 (gray + alpha), spp == 3 (rgb), spp == 4 (rgba) */ d = 4 * bit_depth; } /* Remove if/when this is implemented for all bit_depths */ if (spp == 3 && bit_depth != 8) { fprintf(stderr, "Help: spp = 3 and depth = %d != 8\n!!", bit_depth); png_destroy_read_struct(&png_ptr, &info_ptr, &end_info); return (PIX *)ERROR_PTR("not implemented for this depth", procName, NULL); } if (color_type == PNG_COLOR_TYPE_PALETTE || color_type == PNG_COLOR_MASK_PALETTE) { /* generate a colormap */ png_get_PLTE(png_ptr, info_ptr, &palette, &num_palette); cmap = pixcmapCreate(d); /* spp == 1 */ for (cindex = 0; cindex < num_palette; cindex++) { rval = palette[cindex].red; gval = palette[cindex].green; bval = palette[cindex].blue; pixcmapAddColor(cmap, rval, gval, bval); } } else { cmap = NULL; } if ((pix = pixCreate(w, h, d)) == NULL) { png_destroy_read_struct(&png_ptr, &info_ptr, &end_info); return (PIX *)ERROR_PTR("pix not made", procName, NULL); } wpl = pixGetWpl(pix); data = pixGetData(pix); pixSetColormap(pix, cmap); pixSetSpp(pix, spp); if (spp == 1 && !tRNS) { /* copy straight from buffer to pix */ for (i = 0; i < h; i++) { line = data + i * wpl; rowptr = row_pointers[i]; for (j = 0; j < rowbytes; j++) { SET_DATA_BYTE(line, j, rowptr[j]); } } } else if (spp == 2) { /* grayscale + alpha; convert to RGBA */ L_INFO("converting (gray + alpha) ==> RGBA\n", procName); for (i = 0; i < h; i++) { ppixel = data + i * wpl; rowptr = row_pointers[i]; for (j = k = 0; j < w; j++) { /* Copy gray value into r, g and b */ SET_DATA_BYTE(ppixel, COLOR_RED, rowptr[k]); SET_DATA_BYTE(ppixel, COLOR_GREEN, rowptr[k]); SET_DATA_BYTE(ppixel, COLOR_BLUE, rowptr[k++]); SET_DATA_BYTE(ppixel, L_ALPHA_CHANNEL, rowptr[k++]); ppixel++; } } pixSetSpp(pix, 4); /* we do not support 2 spp pix */ } else if (spp == 3 || spp == 4) { for (i = 0; i < h; i++) { ppixel = data + i * wpl; rowptr = row_pointers[i]; for (j = k = 0; j < w; j++) { SET_DATA_BYTE(ppixel, COLOR_RED, rowptr[k++]); SET_DATA_BYTE(ppixel, COLOR_GREEN, rowptr[k++]); SET_DATA_BYTE(ppixel, COLOR_BLUE, rowptr[k++]); if (spp == 4) SET_DATA_BYTE(ppixel, L_ALPHA_CHANNEL, rowptr[k++]); ppixel++; } } } /* Special case: requires converting to RGBA */ if (spp == 1 && tRNS) { if (!cmap) { /* Trivial case: make fully transparent RGBA image */ L_INFO("transparency, 1 spp, no colormap, no transparency array: " "convention is fully transparent image\n", procName); L_INFO("converting (fully transparent 1 spp) ==> RGBA\n", procName); pixDestroy(&pix); pix = pixCreate(w, h, 32); /* init to alpha = 0 (transparent) */ pixSetSpp(pix, 4); } else { L_INFO("converting (cmap + alpha) ==> RGBA\n", procName); /* Grab the transparency array */ png_get_tRNS(png_ptr, info_ptr, &trans, &num_trans, NULL); if (!trans) { /* invalid png file */ pixDestroy(&pix); png_destroy_read_struct(&png_ptr, &info_ptr, &end_info); return (PIX *)ERROR_PTR("cmap, tRNS, but no transparency array", procName, NULL); } /* Save the cmap and destroy the pix */ cmap = pixcmapCopy(pixGetColormap(pix)); ncolors = pixcmapGetCount(cmap); pixDestroy(&pix); /* Start over with 32 bit RGBA */ pix = pixCreate(w, h, 32); wpl = pixGetWpl(pix); data = pixGetData(pix); pixSetSpp(pix, 4); #if DEBUG_READ fprintf(stderr, "ncolors = %d, num_trans = %d\n", ncolors, num_trans); for (i = 0; i < ncolors; i++) { pixcmapGetColor(cmap, i, &rval, &gval, &bval); if (i < num_trans) { fprintf(stderr, "(r,g,b,a) = (%d,%d,%d,%d)\n", rval, gval, bval, trans[i]); } else { fprintf(stderr, "(r,g,b,a) = (%d,%d,%d,<<255>>)\n", rval, gval, bval); } } #endif /* DEBUG_READ */ /* Extract the data and convert to RGBA */ for (i = 0; i < h; i++) { ppixel = data + i * wpl; rowptr = row_pointers[i]; for (j = 0; j < w; j++) { index = rowptr[j]; pixcmapGetColor(cmap, index, &rval, &gval, &bval); composeRGBPixel(rval, gval, bval, ppixel); /* Assume missing entries to be 255 (opaque) according * to the spec: http://www.w3.org/TR/PNG/#11tRNS */ SET_DATA_BYTE(ppixel, L_ALPHA_CHANNEL, index < num_trans ? trans[index] : 255); ppixel++; } } pixcmapDestroy(&cmap); } } #if DEBUG_READ if (cmap) { for (i = 0; i < 16; i++) { fprintf(stderr, "[%d] = %d\n", i, ((l_uint8 *)(cmap->array))[i]); } } #endif /* DEBUG_READ */ /* If there is no colormap, PNG defines black = 0 and * white = 1 by default for binary monochrome. Therefore, * since we use the opposite definition, we must invert * the image colors in either of these cases: * (i) there is no colormap (default) * (ii) there is a colormap which defines black to * be 0 and white to be 1. * We cannot use the PNG_TRANSFORM_INVERT_MONO flag * because that flag (since version 1.0.9) inverts 8 bpp * grayscale as well, which we don't want to do. * (It also doesn't work if there is a colormap.) * If there is a colormap that defines black = 1 and * white = 0, we don't need to do anything. * * How do we check the polarity of the colormap? * The colormap determines the values of black and * white pixels in the following way: * if black = 1 (255), white = 0 * 255, 255, 255, 0, 0, 0, 0, 0, 0 * if black = 0, white = 1 (255) * 0, 0, 0, 0, 255, 255, 255, 0 * So we test the first byte to see if it is 0; * if so, invert the colors. * * If there is a colormap, after inverting the pixels it is * necessary to destroy the colormap. Otherwise, if someone were * to call pixRemoveColormap(), this would cause the pixel * values to be inverted again! */ if (d == 1 && (!cmap || (cmap && ((l_uint8 *)(cmap->array))[0] == 0x0))) { /* fprintf(stderr, "Inverting binary data on png read\n"); */ pixInvert(pix, pix); pixDestroyColormap(pix); } xres = png_get_x_pixels_per_meter(png_ptr, info_ptr); yres = png_get_y_pixels_per_meter(png_ptr, info_ptr); pixSetXRes(pix, (l_int32)((l_float32)xres / 39.37 + 0.5)); /* to ppi */ pixSetYRes(pix, (l_int32)((l_float32)yres / 39.37 + 0.5)); /* to ppi */ /* Get the text if there is any */ png_get_text(png_ptr, info_ptr, &text_ptr, &num_text); if (num_text && text_ptr) pixSetText(pix, text_ptr->text); png_destroy_read_struct(&png_ptr, &info_ptr, &end_info); return pix; } /*! * readHeaderPng() * * Input: filename * &w () * &h () * &bps (, bits/sample) * &spp (, samples/pixel) * &iscmap () * Return: 0 if OK, 1 on error * * Notes: * (1) If there is a colormap, iscmap is returned as 1; else 0. * (2) For gray+alpha, although the png records bps = 16, we * consider this as two 8 bpp samples (gray and alpha). * When a gray+alpha is read, it is converted to 32 bpp RGBA. */ l_int32 readHeaderPng(const char *filename, l_int32 *pw, l_int32 *ph, l_int32 *pbps, l_int32 *pspp, l_int32 *piscmap) { l_int32 ret; FILE *fp; PROCNAME("readHeaderPng"); if (!filename) return ERROR_INT("filename not defined", procName, 1); if ((fp = fopenReadStream(filename)) == NULL) return ERROR_INT("image file not found", procName, 1); ret = freadHeaderPng(fp, pw, ph, pbps, pspp, piscmap); fclose(fp); return ret; } /*! * freadHeaderPng() * * Input: stream * &w () * &h () * &bps (, bits/sample) * &spp (, samples/pixel) * &iscmap () * Return: 0 if OK, 1 on error * * Notes: * (1) See readHeaderPng(). */ l_int32 freadHeaderPng(FILE *fp, l_int32 *pw, l_int32 *ph, l_int32 *pbps, l_int32 *pspp, l_int32 *piscmap) { l_int32 nbytes, ret; l_uint8 *data; PROCNAME("freadHeaderPng"); if (pw) *pw = 0; if (ph) *ph = 0; if (pbps) *pbps = 0; if (pspp) *pspp = 0; if (piscmap) *piscmap = 0; if (!fp) return ERROR_INT("stream not defined", procName, 1); nbytes = fnbytesInFile(fp); if (nbytes < 40) return ERROR_INT("file too small to be png", procName, 1); if ((data = (l_uint8 *)CALLOC(40, sizeof(l_uint8))) == NULL) return ERROR_INT("CALLOC fail for data", procName, 1); if (fread(data, 1, 40, fp) != 40) return ERROR_INT("error reading data", procName, 1); ret = sreadHeaderPng(data, pw, ph, pbps, pspp, piscmap); FREE(data); return ret; } /*! * sreadHeaderPng() * * Input: data * &w () * &h () * &bps (, bits/sample) * &spp (, samples/pixel) * &iscmap (; input NULL to ignore) * Return: 0 if OK, 1 on error * * Notes: * (1) See readHeaderPng(). * (2) png colortypes (see png.h: PNG_COLOR_TYPE_*): * 0: gray; fully transparent (with tRNS) (1 spp) * 2: RGB (3 spp) * 3: colormap; colormap+alpha (with tRNS) (1 spp) * 4: gray + alpha (2 spp) * 6: RGBA (4 spp) * Note: * 0 and 3 have the alpha information in a tRNS chunk * 4 and 6 have separate alpha samples with each pixel. */ l_int32 sreadHeaderPng(const l_uint8 *data, l_int32 *pw, l_int32 *ph, l_int32 *pbps, l_int32 *pspp, l_int32 *piscmap) { l_uint16 twobytes; l_uint16 *pshort; l_int32 colortype, bps, spp; l_uint32 *pword; PROCNAME("sreadHeaderPng"); if (!data) return ERROR_INT("data not defined", procName, 1); if (pw) *pw = 0; if (ph) *ph = 0; if (pbps) *pbps = 0; if (pspp) *pspp = 0; if (piscmap) *piscmap = 0; /* Check password */ if (data[0] != 137 || data[1] != 80 || data[2] != 78 || data[3] != 71 || data[4] != 13 || data[5] != 10 || data[6] != 26 || data[7] != 10) return ERROR_INT("not a valid png file", procName, 1); pword = (l_uint32 *)data; pshort = (l_uint16 *)data; if (pw) *pw = convertOnLittleEnd32(pword[4]); if (ph) *ph = convertOnLittleEnd32(pword[5]); twobytes = convertOnLittleEnd16(pshort[12]); /* contains depth/sample */ /* and the color type */ colortype = twobytes & 0xff; /* color type */ bps = twobytes >> 8; /* bits/sample */ /* Special case with alpha that is extracted as RGBA. * Note that the cmap+alpha is also extracted as RGBA, * but only if the tRNS chunk exists, which we can't tell * by this simple parser.*/ if (colortype == 4) L_INFO("gray + alpha: will extract as RGBA (spp = 4)\n", procName); if (colortype == 2) { /* RGB */ spp = 3; } else if (colortype == 6) { /* RGBA */ spp = 4; } else if (colortype == 4) { /* gray + alpha */ spp = 2; bps = 8; /* both the gray and alpha are 8-bit samples */ } else { /* gray (0) or cmap (3) or cmap+alpha (3) */ spp = 1; } if (pbps) *pbps = bps; if (pspp) *pspp = spp; if (piscmap) { if (colortype & 1) /* palette */ *piscmap = 1; else *piscmap = 0; } return 0; } /* * fgetPngResolution() * * Input: stream (opened for read) * &xres, &yres ( resolution in ppi) * Return: 0 if OK; 0 on error * * Notes: * (1) If neither resolution field is set, this is not an error; * the returned resolution values are 0 (designating 'unknown'). * (2) Side-effect: this rewinds the stream. */ l_int32 fgetPngResolution(FILE *fp, l_int32 *pxres, l_int32 *pyres) { png_uint_32 xres, yres; png_structp png_ptr; png_infop info_ptr; PROCNAME("fgetPngResolution"); if (!pxres || !pyres) return ERROR_INT("&xres and &yres not both defined", procName, 1); *pxres = *pyres = 0; if (!fp) return ERROR_INT("stream not opened", procName, 1); /* Make the two required structs */ if ((png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, (png_voidp)NULL, NULL, NULL)) == NULL) return ERROR_INT("png_ptr not made", procName, 1); if ((info_ptr = png_create_info_struct(png_ptr)) == NULL) { png_destroy_read_struct(&png_ptr, (png_infopp)NULL, (png_infopp)NULL); return ERROR_INT("info_ptr not made", procName, 1); } /* Set up png setjmp error handling. * Without this, an error calls exit. */ if (setjmp(png_jmpbuf(png_ptr))) { png_destroy_read_struct(&png_ptr, &info_ptr, (png_infopp)NULL); return ERROR_INT("internal png error", procName, 1); } /* Read the metadata */ rewind(fp); png_init_io(png_ptr, fp); png_read_png(png_ptr, info_ptr, 0, NULL); xres = png_get_x_pixels_per_meter(png_ptr, info_ptr); yres = png_get_y_pixels_per_meter(png_ptr, info_ptr); *pxres = (l_int32)((l_float32)xres / 39.37 + 0.5); /* to ppi */ *pyres = (l_int32)((l_float32)yres / 39.37 + 0.5); png_destroy_read_struct(&png_ptr, &info_ptr, NULL); rewind(fp); return 0; } /*---------------------------------------------------------------------* * Writing png * *---------------------------------------------------------------------*/ /*! * pixWritePng() * * Input: filename * pix * gamma * Return: 0 if OK; 1 on error * * Notes: * (1) Special version for writing png with a specified gamma. * When using pixWrite(), no field is given for gamma. */ l_int32 pixWritePng(const char *filename, PIX *pix, l_float32 gamma) { FILE *fp; PROCNAME("pixWritePng"); if (!pix) return ERROR_INT("pix not defined", procName, 1); if (!filename) return ERROR_INT("filename not defined", procName, 1); if ((fp = fopenWriteStream(filename, "wb+")) == NULL) return ERROR_INT("stream not opened", procName, 1); if (pixWriteStreamPng(fp, pix, gamma)) { fclose(fp); return ERROR_INT("pix not written to stream", procName, 1); } fclose(fp); return 0; } /*! * pixWriteStreamPng() * * Input: stream * pix * gamma (use 0.0 if gamma is not defined) * Return: 0 if OK; 1 on error * * Notes: * (1) If called from pixWriteStream(), the stream is positioned * at the beginning of the file. * (2) To do sequential writes of png format images to a stream, * use pixWriteStreamPng() directly. * (3) gamma is an optional png chunk. If no gamma value is to be * placed into the file, use gamma = 0.0. Otherwise, if * gamma > 0.0, its value is written into the header. * (4) The use of gamma in png is highly problematic. For an illuminating * discussion, see: http://hsivonen.iki.fi/png-gamma/ * (5) What is the effect/meaning of gamma in the png file? This * gamma, which we can call the 'source' gamma, is the * inverse of the gamma that was used in enhance.c to brighten * or darken images. The 'source' gamma is supposed to indicate * the intensity mapping that was done at the time the * image was captured. Display programs typically apply a * 'display' gamma of 2.2 to the output, which is intended * to linearize the intensity based on the response of * thermionic tubes (CRTs). Flat panel LCDs have typically * been designed to give a similar response as CRTs (call it * "backward compatibility"). The 'display' gamma is * in some sense the inverse of the 'source' gamma. * jpeg encoders attached to scanners and cameras will lighten * the pixels, applying a gamma corresponding to approximately * a square-root relation of output vs input: * output = input^(gamma) * where gamma is often set near 0.4545 (1/gamma is 2.2). * This is stored in the image file. Then if the display * program reads the gamma, it will apply a display gamma, * typically about 2.2; the product is 1.0, and the * display program produces a linear output. This works because * the dark colors were appropriately boosted by the scanner, * as described by the 'source' gamma, so they should not * be further boosted by the display program. * (6) As an example, with xv and display, if no gamma is stored, * the program acts as if gamma were 0.4545, multiplies this by 2.2, * and does a linear rendering. Taking this as a baseline * brightness, if the stored gamma is: * > 0.4545, the image is rendered lighter than baseline * < 0.4545, the image is rendered darker than baseline * In contrast, gqview seems to ignore the gamma chunk in png. * (7) The only valid pixel depths in leptonica are 1, 2, 4, 8, 16 * and 32. However, it is possible, and in some cases desirable, * to write out a png file using an rgb pix that has 24 bpp. * For example, the open source xpdf SplashBitmap class generates * 24 bpp rgb images. Consequently, we enable writing 24 bpp pix. * To generate such a pix, you can make a 24 bpp pix without data * and assign the data array to the pix; e.g., * pix = pixCreateHeader(w, h, 24); * pixSetData(pix, rgbdata); * See pixConvert32To24() for an example, where we get rgbdata * from the 32 bpp pix. Caution: do not call pixSetPadBits(), * because the alignment is wrong and you may erase part of the * last pixel on each line. * (8) If the pix has a colormap, it is written to file. In most * situations, the alpha component is 255 for each colormap entry, * which is opaque and indicates that it should be ignored. * However, if any alpha component is not 255, it is assumed that * the alpha values are valid, and they are written to the png * file in a tRNS segment. On readback, the tRNS segment is * identified, and the colormapped image with alpha is converted * to a 4 spp rgba image. */ l_int32 pixWriteStreamPng(FILE *fp, PIX *pix, l_float32 gamma) { char commentstring[] = "Comment"; l_int32 i, j, k; l_int32 wpl, d, spp, cmflag, opaque; l_int32 ncolors, compval; l_int32 *rmap, *gmap, *bmap, *amap; l_uint32 *data, *ppixel; png_byte bit_depth, color_type; png_byte alpha[256]; png_uint_32 w, h; png_uint_32 xres, yres; png_bytep *row_pointers; png_bytep rowbuffer; png_structp png_ptr; png_infop info_ptr; png_colorp palette; PIX *pixt; PIXCMAP *cmap; char *text; PROCNAME("pixWriteStreamPng"); if (!fp) return ERROR_INT("stream not open", procName, 1); if (!pix) return ERROR_INT("pix not defined", procName, 1); /* Allocate the 2 data structures */ if ((png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, (png_voidp)NULL, NULL, NULL)) == NULL) return ERROR_INT("png_ptr not made", procName, 1); if ((info_ptr = png_create_info_struct(png_ptr)) == NULL) { png_destroy_write_struct(&png_ptr, (png_infopp)NULL); return ERROR_INT("info_ptr not made", procName, 1); } /* Set up png setjmp error handling */ if (setjmp(png_jmpbuf(png_ptr))) { png_destroy_write_struct(&png_ptr, &info_ptr); return ERROR_INT("internal png error", procName, 1); } png_init_io(png_ptr, fp); /* With best zlib compression (9), get between 1 and 10% improvement * over default (6), but the compression is 3 to 10 times slower. * Use the zlib default (6) as our default compression unless * pix->special falls in the range [10 ... 19]; then subtract 10 * to get the compression value. */ compval = Z_DEFAULT_COMPRESSION; if (pix->special >= 10 && pix->special < 20) compval = pix->special - 10; png_set_compression_level(png_ptr, compval); w = pixGetWidth(pix); h = pixGetHeight(pix); d = pixGetDepth(pix); spp = pixGetSpp(pix); if ((cmap = pixGetColormap(pix))) cmflag = 1; else cmflag = 0; /* Set the color type and bit depth. */ if (d == 32 && spp == 4) { bit_depth = 8; color_type = PNG_COLOR_TYPE_RGBA; /* 6 */ cmflag = 0; /* ignore if it exists */ } else if (d == 24 || d == 32) { bit_depth = 8; color_type = PNG_COLOR_TYPE_RGB; /* 2 */ cmflag = 0; /* ignore if it exists */ } else { bit_depth = d; color_type = PNG_COLOR_TYPE_GRAY; /* 0 */ } if (cmflag) color_type = PNG_COLOR_TYPE_PALETTE; /* 3 */ #if DEBUG_WRITE fprintf(stderr, "cmflag = %d, bit_depth = %d, color_type = %d\n", cmflag, bit_depth, color_type); #endif /* DEBUG_WRITE */ png_set_IHDR(png_ptr, info_ptr, w, h, bit_depth, color_type, PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_BASE, PNG_FILTER_TYPE_BASE); /* Store resolution in ppm, if known */ xres = (png_uint_32)(39.37 * (l_float32)pixGetXRes(pix) + 0.5); yres = (png_uint_32)(39.37 * (l_float32)pixGetYRes(pix) + 0.5); if ((xres == 0) || (yres == 0)) png_set_pHYs(png_ptr, info_ptr, 0, 0, PNG_RESOLUTION_UNKNOWN); else png_set_pHYs(png_ptr, info_ptr, xres, yres, PNG_RESOLUTION_METER); if (cmflag) { pixcmapToArrays(cmap, &rmap, &gmap, &bmap, &amap); ncolors = pixcmapGetCount(cmap); pixcmapIsOpaque(cmap, &opaque); /* Make and save the palette */ if ((palette = (png_colorp)(CALLOC(ncolors, sizeof(png_color)))) == NULL) return ERROR_INT("palette not made", procName, 1); for (i = 0; i < ncolors; i++) { palette[i].red = (png_byte)rmap[i]; palette[i].green = (png_byte)gmap[i]; palette[i].blue = (png_byte)bmap[i]; alpha[i] = (png_byte)amap[i]; } png_set_PLTE(png_ptr, info_ptr, palette, (int)ncolors); if (!opaque) /* alpha channel has some transparency; assume valid */ png_set_tRNS(png_ptr, info_ptr, (png_bytep)alpha, (int)ncolors, NULL); FREE(rmap); FREE(gmap); FREE(bmap); FREE(amap); } /* 0.4545 is treated as the default by some image * display programs (not gqview). A value > 0.4545 will * lighten an image as displayed by xv, display, etc. */ if (gamma > 0.0) png_set_gAMA(png_ptr, info_ptr, (l_float64)gamma); if ((text = pixGetText(pix))) { png_text text_chunk; text_chunk.compression = PNG_TEXT_COMPRESSION_NONE; text_chunk.key = commentstring; text_chunk.text = text; text_chunk.text_length = strlen(text); #ifdef PNG_ITXT_SUPPORTED text_chunk.itxt_length = 0; text_chunk.lang = NULL; text_chunk.lang_key = NULL; #endif png_set_text(png_ptr, info_ptr, &text_chunk, 1); } /* Write header and palette info */ png_write_info(png_ptr, info_ptr); if ((d != 32) && (d != 24)) { /* not rgb color */ /* Generate a temporary pix with bytes swapped. * For a binary image, there are two conditions in * which you must first invert the data for writing png: * (a) no colormap * (b) colormap with BLACK set to 0 * png writes binary with BLACK = 0, unless contradicted * by a colormap. If the colormap has BLACK = "1" * (typ. about 255), do not invert the data. If there * is no colormap, you must invert the data to store * in default BLACK = 0 state. */ if (d == 1 && (!cmap || (cmap && ((l_uint8 *)(cmap->array))[0] == 0x0))) { pixt = pixInvert(NULL, pix); pixEndianByteSwap(pixt); } else { pixt = pixEndianByteSwapNew(pix); } if (!pixt) { png_destroy_write_struct(&png_ptr, &info_ptr); return ERROR_INT("pixt not made", procName, 1); } /* Make and assign array of image row pointers */ if ((row_pointers = (png_bytep *)CALLOC(h, sizeof(png_bytep))) == NULL) return ERROR_INT("row-pointers not made", procName, 1); wpl = pixGetWpl(pixt); data = pixGetData(pixt); for (i = 0; i < h; i++) row_pointers[i] = (png_bytep)(data + i * wpl); png_set_rows(png_ptr, info_ptr, row_pointers); /* Transfer the data */ png_write_image(png_ptr, row_pointers); png_write_end(png_ptr, info_ptr); if (cmflag) FREE(palette); FREE(row_pointers); pixDestroy(&pixt); png_destroy_write_struct(&png_ptr, &info_ptr); return 0; } /* For rgb, compose and write a row at a time */ data = pixGetData(pix); wpl = pixGetWpl(pix); if (d == 24) { /* See note 7 above: special case of 24 bpp rgb */ for (i = 0; i < h; i++) { ppixel = data + i * wpl; png_write_rows(png_ptr, (png_bytepp)&ppixel, 1); } } else { /* 32 bpp rgb and rgba. Write out the alpha channel if either * the pix has 4 spp or writing it is requested anyway */ if ((rowbuffer = (png_bytep)CALLOC(w, 4)) == NULL) return ERROR_INT("rowbuffer not made", procName, 1); for (i = 0; i < h; i++) { ppixel = data + i * wpl; for (j = k = 0; j < w; j++) { rowbuffer[k++] = GET_DATA_BYTE(ppixel, COLOR_RED); rowbuffer[k++] = GET_DATA_BYTE(ppixel, COLOR_GREEN); rowbuffer[k++] = GET_DATA_BYTE(ppixel, COLOR_BLUE); if (spp == 4) rowbuffer[k++] = GET_DATA_BYTE(ppixel, L_ALPHA_CHANNEL); ppixel++; } png_write_rows(png_ptr, &rowbuffer, 1); } FREE(rowbuffer); } png_write_end(png_ptr, info_ptr); if (cmflag) FREE(palette); png_destroy_write_struct(&png_ptr, &info_ptr); return 0; } /*! * pixSetZlibCompression() * * Input: pix * compval (zlib compression value) * Return: 0 if OK, 1 on error * * Notes: * (1) Valid zlib compression values are in the interval [0 ... 9], * where, as defined in zlib.h: * 0 Z_NO_COMPRESSION * 1 Z_BEST_SPEED (poorest compression) * 9 Z_BEST_COMPRESSION * For the default value, use either of these: * 6 Z_DEFAULT_COMPRESSION * -1 (resolves to Z_DEFAULT_COMPRESSION) * (2) If you use the defined constants in zlib.h instead of the * compression integers given above, you must include zlib.h. */ l_int32 pixSetZlibCompression(PIX *pix, l_int32 compval) { PROCNAME("pixSetZlibCompression"); if (!pix) return ERROR_INT("pix not defined", procName, 1); if (compval < 0 || compval > 9) { L_ERROR("Invalid zlib comp val; using default\n", procName); compval = Z_DEFAULT_COMPRESSION; } pix->special = 10 + compval; /* valid range [10 ... 19] */ return 0; } /*---------------------------------------------------------------------* * Setting flag for stripping 16 bits on reading * *---------------------------------------------------------------------*/ /*! * l_pngSetReadStrip16To8() * * Input: flag (1 for stripping 16 bpp to 8 bpp on reading; * 0 for leaving 16 bpp) * Return: void */ void l_pngSetReadStrip16To8(l_int32 flag) { var_PNG_STRIP_16_TO_8 = flag; } /*---------------------------------------------------------------------* * Read/write to memory * *---------------------------------------------------------------------*/ #if HAVE_FMEMOPEN extern FILE *open_memstream(char **data, size_t *size); extern FILE *fmemopen(void *data, size_t size, const char *mode); #endif /* HAVE_FMEMOPEN */ /*! * pixReadMemPng() * * Input: cdata (const; png-encoded) * size (of data) * Return: pix, or null on error * * Notes: * (1) The @size byte of @data must be a null character. */ PIX * pixReadMemPng(const l_uint8 *cdata, size_t size) { FILE *fp; PIX *pix; PROCNAME("pixReadMemPng"); if (!cdata) return (PIX *)ERROR_PTR("cdata not defined", procName, NULL); #if HAVE_FMEMOPEN if ((fp = fmemopen((void *)cdata, size, "r")) == NULL) return (PIX *)ERROR_PTR("stream not opened", procName, NULL); #else L_WARNING("work-around: writing to a temp file\n", procName); fp = tmpfile(); fwrite(cdata, 1, size, fp); rewind(fp); #endif /* HAVE_FMEMOPEN */ pix = pixReadStreamPng(fp); fclose(fp); if (!pix) L_ERROR("pix not read\n", procName); return pix; } /*! * pixWriteMemPng() * * Input: &data ( data of tiff compressed image) * &size ( size of returned data) * pix * gamma (use 0.0 if gamma is not defined) * Return: 0 if OK, 1 on error * * Notes: * (1) See pixWriteStreamPng() for usage. This version writes to * memory instead of to a file stream. */ l_int32 pixWriteMemPng(l_uint8 **pdata, size_t *psize, PIX *pix, l_float32 gamma) { l_int32 ret; FILE *fp; PROCNAME("pixWriteMemPng"); if (!pdata) return ERROR_INT("&data not defined", procName, 1 ); if (!psize) return ERROR_INT("&size not defined", procName, 1 ); if (!pix) return ERROR_INT("&pix not defined", procName, 1 ); #if HAVE_FMEMOPEN if ((fp = open_memstream((char **)pdata, psize)) == NULL) return ERROR_INT("stream not opened", procName, 1); ret = pixWriteStreamPng(fp, pix, gamma); #else L_WARNING("work-around: writing to a temp file\n", procName); fp = tmpfile(); ret = pixWriteStreamPng(fp, pix, gamma); rewind(fp); *pdata = l_binaryReadStream(fp, psize); #endif /* HAVE_FMEMOPEN */ fclose(fp); return ret; } /* --------------------------------------------*/ #endif /* HAVE_LIBPNG */ /* --------------------------------------------*/