Tesseract doesn't appear to work well with a bitmap, works on some inputs but screws up others. While at the same time performs fine on inputs that are identical to previous but in leptonica's format PIX.
How can I convert a bitmap in memory to PIX?
One idea that came to mind is to use leptonica's pixReadMem() :
00724 /*---------------------------------------------------------------------*
00725 * Read from memory *
00726 *---------------------------------------------------------------------*/
00727 /*!
00728 * pixReadMem()
00729 *
00730 * Input: data (const; encoded)
00731 * datasize (size of data)
00732 * Return: pix, or null on error
00733 *
00734 * Notes:
00735 * (1) This is a variation of pixReadStream(), where the data is read
00736 * from a memory buffer rather than a file.
00737 * (2) On windows, this will only read tiff formatted files from
00738 * memory. For other formats, it requires fmemopen(3).
00739 * Attempts to read those formats will fail at runtime.
00740 * (3) findFileFormatBuffer() requires up to 8 bytes to decide on
00741 * the format. That determines the constraint here.
00742 */
So now I need to find a way to construct a TIFF in memory from a bitmap in memory. But I don't know how.
Well I decided to just do this myself with a quick dirty port. I just took the file loading BMP function and created fake fread/fseek since I am really lazy. Works.
In case anyone needs it I will post it below. It's baffling why leptonica developers didn't do it for windows properly.
#include <cstring>
#include <leptonica/allheaders.h>
#include "leptonica_hack.h"
#include "bmp.h"
int fake_file_tracker = 0;
size_t fake_fread ( void * ptr, size_t size, size_t count, char * buffer, size_t buflen)
{
if (fake_file_tracker >= buflen)
{
return 0;
}
if (fake_file_tracker + size * count > buflen)
{
(void)memcpy(ptr, (void *)(buffer+fake_file_tracker), (size_t)(buflen - fake_file_tracker));
fake_file_tracker = buflen+1;
return (size_t)((buflen - fake_file_tracker) / size);
}
(void)memcpy(ptr, (void *)(buffer+fake_file_tracker), size * count);
fake_file_tracker += size * count;
return count;
}
int fake_fseek ( char * buffer, long int offset, int origin, size_t buflen)
{
if (origin + offset >= buflen)
return 0;
fake_file_tracker = origin + offset;
return 0;
}
/*!
* pixReadStreamBmp()
*
* Input: stream opened for read
* Return: pix, or null on error
*
* Notes:
* (1) Here are references on the bmp file format:
* http://en.wikipedia.org/wiki/BMP_file_format
* http://www.fortunecity.com/skyscraper/windows/364/bmpffrmt.html
*/
PIX *
pixReadBmpFromBuffer(char *fp, size_t buflen)
{
fake_file_tracker = 0;
l_uint16 sval;
l_uint32 ival;
l_int16 bfType, bfSize, bfFill1, bfReserved1, bfReserved2;
l_int16 offset, bfFill2, biPlanes, depth, d;
l_int32 biSize, width, height, xres, yres, compression, ignore;
l_int32 imagebytes, biClrUsed, biClrImportant;
l_uint8 *colormapBuf = NULL;
l_int32 colormapEntries;
l_int32 fileBpl, extrabytes, readerror;
l_int32 pixWpl, pixBpl;
l_int32 i, j, k;
l_uint8 pel[4];
l_uint8 *data;
l_uint32 *line, *pword;
PIX *pix, *pixt;
PIXCMAP *cmap;
PROCNAME("pixReadBmpFromBuffer");
if (!fp)
return (PIX *)ERROR_PTR("fp not defined", procName, NULL);
/* Read bitmap file header */
ignore = fake_fread((char *)&sval, 1, 2, fp, buflen);
bfType = convertOnBigEnd16(sval);
if (bfType != BMP_ID)
return (PIX *)ERROR_PTR("not bmf format", procName, NULL);
ignore = fake_fread((char *)&sval, 1, 2, fp, buflen);
bfSize = convertOnBigEnd16(sval);
ignore = fake_fread((char *)&sval, 1, 2, fp, buflen);
bfFill1 = convertOnBigEnd16(sval);
ignore = fake_fread((char *)&sval, 1, 2, fp, buflen);
bfReserved1 = convertOnBigEnd16(sval);
ignore = fake_fread((char *)&sval, 1, 2, fp, buflen);
bfReserved2 = convertOnBigEnd16(sval);
ignore = fake_fread((char *)&sval, 1, 2, fp, buflen);
offset = convertOnBigEnd16(sval);
ignore = fake_fread((char *)&sval, 1, 2, fp, buflen);
bfFill2 = convertOnBigEnd16(sval);
/* Read bitmap info header */
ignore = fake_fread((char *)&ival, 1, 4, fp, buflen);
biSize = convertOnBigEnd32(ival);
ignore = fake_fread((char *)&ival, 1, 4, fp, buflen);
width = convertOnBigEnd32(ival);
ignore = fake_fread((char *)&ival, 1, 4, fp, buflen);
height = convertOnBigEnd32(ival);
ignore = fake_fread((char *)&sval, 1, 2, fp, buflen);
biPlanes = convertOnBigEnd16(sval);
ignore = fake_fread((char *)&sval, 1, 2, fp, buflen);
depth = convertOnBigEnd16(sval);
ignore = fake_fread((char *)&ival, 1, 4, fp, buflen);
compression = convertOnBigEnd32(ival);
ignore = fake_fread((char *)&ival, 1, 4, fp, buflen);
imagebytes = convertOnBigEnd32(ival);
ignore = fake_fread((char *)&ival, 1, 4, fp, buflen);
xres = convertOnBigEnd32(ival);
ignore = fake_fread((char *)&ival, 1, 4, fp, buflen);
yres = convertOnBigEnd32(ival);
ignore = fake_fread((char *)&ival, 1, 4, fp, buflen);
biClrUsed = convertOnBigEnd32(ival);
ignore = fake_fread((char *)&ival, 1, 4, fp, buflen);
biClrImportant = convertOnBigEnd32(ival);
if (compression != 0)
return (PIX *)ERROR_PTR("cannot read compressed BMP files",
procName,NULL);
/* A little sanity checking. It would be nice to check
* if the number of bytes in the file equals the offset to
* the data plus the imagedata, but this won't work when
* reading from memory, because fmemopen() doesn't implement
* ftell(). So we can't do that check. The imagebytes for
* uncompressed images is either 0 or the size of the file data.
* (The fact that it can be 0 is perhaps some legacy glitch). */
if (width < 1)
return (PIX *)ERROR_PTR("width < 1", procName,NULL);
if (height < 1)
return (PIX *)ERROR_PTR("height < 1", procName,NULL);
if (depth < 1 || depth > 32)
return (PIX *)ERROR_PTR("depth not in [1 ... 32]", procName,NULL);
fileBpl = 4 * ((width * depth + 31)/32);
if (imagebytes != 0 && imagebytes != fileBpl * height)
return (PIX *)ERROR_PTR("invalid imagebytes", procName,NULL);
if (offset < BMP_FHBYTES + BMP_IHBYTES)
return (PIX *)ERROR_PTR("invalid offset: too small", procName,NULL);
if (offset > BMP_FHBYTES + BMP_IHBYTES + 4 * 256)
return (PIX *)ERROR_PTR("invalid offset: too large", procName,NULL);
/* Handle the colormap */
colormapEntries = (offset - BMP_FHBYTES - BMP_IHBYTES) / sizeof(RGBA_QUAD);
if (colormapEntries > 0) {
if ((colormapBuf = (l_uint8 *)CALLOC(colormapEntries,
sizeof(RGBA_QUAD))) == NULL)
return (PIX *)ERROR_PTR("colormapBuf alloc fail", procName, NULL );
/* Read colormap */
if (fake_fread(colormapBuf, sizeof(RGBA_QUAD), colormapEntries, fp, buflen)
!= colormapEntries) {
FREE(colormapBuf);
return (PIX *)ERROR_PTR( "colormap read fail", procName, NULL);
}
}
/* Make a 32 bpp pix if depth is 24 bpp */
d = depth;
if (depth == 24)
d = 32;
if ((pix = pixCreate(width, height, d)) == NULL)
return (PIX *)ERROR_PTR( "pix not made", procName, NULL);
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 */
pixWpl = pixGetWpl(pix);
pixBpl = 4 * pixWpl;
cmap = NULL;
if (colormapEntries > 256)
L_WARNING("more than 256 colormap entries!", procName);
if (colormapEntries > 0) { /* import the colormap to the pix cmap */
cmap = pixcmapCreate(L_MIN(d, 8));
FREE(cmap->array); /* remove generated cmap array */
cmap->array = (void *)colormapBuf; /* and replace */
cmap->n = L_MIN(colormapEntries, 256);
}
pixSetColormap(pix, cmap);
/* Seek to the start of the bitmap in the file */
fake_fseek(fp, offset, 0, buflen);
if (depth != 24) { /* typ. 1 or 8 bpp */
data = (l_uint8 *)pixGetData(pix) + pixBpl * (height - 1);
for (i = 0; i < height; i++) {
if (fake_fread(data, 1, fileBpl, fp, buflen) != fileBpl) {
pixDestroy(&pix);
return (PIX *)ERROR_PTR("BMP read fail", procName, NULL);
}
data -= pixBpl;
}
}
else { /* 24 bpp file; 32 bpp pix
* Note: for bmp files, pel[0] is blue, pel[1] is green,
* and pel[2] is red. This is opposite to the storage
* in the pix, which puts the red pixel in the 0 byte,
* the green in the 1 byte and the blue in the 2 byte.
* Note also that all words are endian flipped after
* assignment on L_LITTLE_ENDIAN platforms.
*
* We can then make these assignments for little endians:
* SET_DATA_BYTE(pword, 1, pel[0]); blue
* SET_DATA_BYTE(pword, 2, pel[1]); green
* SET_DATA_BYTE(pword, 3, pel[2]); red
* This looks like:
* 3 (R) 2 (G) 1 (B) 0
* |-----------|------------|-----------|-----------|
* and after byte flipping:
* 3 2 (B) 1 (G) 0 (R)
* |-----------|------------|-----------|-----------|
*
* For big endians we set:
* SET_DATA_BYTE(pword, 2, pel[0]); blue
* SET_DATA_BYTE(pword, 1, pel[1]); green
* SET_DATA_BYTE(pword, 0, pel[2]); red
* This looks like:
* 0 (R) 1 (G) 2 (B) 3
* |-----------|------------|-----------|-----------|
* so in both cases we get the correct assignment in the PIX.
*
* Can we do a platform-independent assignment?
* Yes, set the bytes without using macros:
* *((l_uint8 *)pword) = pel[2]; red
* *((l_uint8 *)pword + 1) = pel[1]; green
* *((l_uint8 *)pword + 2) = pel[0]; blue
* For little endians, before flipping, this looks again like:
* 3 (R) 2 (G) 1 (B) 0
* |-----------|------------|-----------|-----------|
*/
readerror = 0;
extrabytes = fileBpl - 3 * width;
line = pixGetData(pix) + pixWpl * (height - 1);
for (i = 0; i < height; i++) {
for (j = 0; j < width; j++) {
pword = line + j;
if (fake_fread(&pel, 1, 3, fp, buflen) != 3)
readerror = 1;
*((l_uint8 *)pword + COLOR_RED) = pel[2];
*((l_uint8 *)pword + COLOR_GREEN) = pel[1];
*((l_uint8 *)pword + COLOR_BLUE) = pel[0];
}
if (extrabytes) {
for (k = 0; k < extrabytes; k++)
ignore = fake_fread(&pel, 1, 1, fp, buflen);
}
line -= pixWpl;
}
if (readerror) {
pixDestroy(&pix);
return (PIX *)ERROR_PTR("BMP read fail", procName, NULL);
}
}
pixEndianByteSwap(pix);
/* ----------------------------------------------
* The bmp colormap determines the values of black
* and white pixels for binary in the following way:
* if black = 1 (255), white = 0
* 255, 255, 255, 0, 0, 0, 0, 0
* if black = 0, white = 1 (255)
* 0, 0, 0, 0, 255, 255, 255, 0
* We have no need for a 1 bpp pix with a colormap!
* ---------------------------------------------- */
if (depth == 1 && cmap) {
/* L_INFO("Removing colormap", procName); */
pixt = pixRemoveColormap(pix, REMOVE_CMAP_BASED_ON_SRC);
pixDestroy(&pix);
pix = pixt; /* rename */
}
return pix;
}