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Fix documentation for cropping images in pdf files.
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@DanBloomberg
DanBloomberg committed Aug 28, 2023
1 parent 1fc4fc8 commit d803c99
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4 changes: 4 additions & 0 deletions prog/cleanpdf.c
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Expand Up @@ -87,6 +87,10 @@
*
* Whenever possible, the images will be deskewed.
*
* As the first step in processing, images are saved in the ./image
* directory as RGB at 300 ppi in ppm format. Each image is about 26MB.
* Delete those images after use.
*
* Some pdf files have oversize media boxes. PDF is a
* resolution-independent format for storing data that can be imaged.
* Usually the data is stored in fonts, which are a description of the
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93 changes: 28 additions & 65 deletions prog/croppdf.c
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Expand Up @@ -28,70 +28,38 @@
* croppdf.c
*
* This program concatenates all pdfs in a directory by rendering them
* as images, optionally scaling the images, and generating an output pdf.
* The pdfs are taken in lexical order. Pages are encoded with either
* tiffg4 or jpeg (DCT), or a mixture of them depending on input parameters
* and page color content. For DCT encoding, the jpeg quality factor
* can be used to trade off the size of the resulting pdf against
* the image quality.
* as images, cropping each image to the foreground region with
* options for noise removal and margins, slightly thickens long
* horizontal lines (e.g., of a music staff), and to some extent
* scales the width to fill a printed page. See documentation for
* pixCropImage() for the parameters.
*
* If the pages are monochrome (black and white), use of the %onebit
* flag will achieve better compression with less distortion.
* If most of the pages are black and white, but some have color that
* needs to be saved, input parameters %onebit and %savecolor should
* be both set to 1. Then the pages with color are compressed with DCT
* and the monochrome pages are compressed with tiffg4.
* The pdfs are concatenated in lexical order, and each image
* is encoded with tiffg4.
*
* The first step is to render the images as RGB, using Poppler's pdftoppm.
* Compare compresspdf with cleanpdf, which carries out several cleanup
* operations, such as deskewing and adaptive thresholding to clean
* noisy or dark backgrounds in grayscale or color images, resulting
* in high resolution, 1 bpp tiffg4 encoded images in the pdf.
*
* Syntax:
* compresspdf basedir scalefactor onebit savecolor quality title fileout
* Syntax:
* croppdf basedir threshold lrclear tbclear edgeclean
* lradd tbadd title fileout
*
* The %basedir is a directory where the input pdf files are located.
* The program will operate on every file in this directory with
* the ".pdf" extension.
*
* The %scalefactor is typically used to downscale the image to
* reduce the size of the generated pdf. It should not affect the
* pdf display otherwise. For normal text on images scanned at 300 ppi,
* a 2x reduction (%scalefactor = 0.5) may be satisfactory.
* We compute an output resolution for that pdf that will cause it
* to print 11 inches high, based on the height in pixels of the
* first image in the set.
*
* Images are saved in the ./image directory as RGB in ppm format.
* If the %onebit flag is 0, these will be encoded in the output pdf
* using DCT. To force the images to be 1 bpp, with tiffg4 encoding, set
* the $onebit flag to 1.
*
* The %savecolor flag is ignored unless %onebit is 1. In that case,
* if %savecolor is 1, the image is tested for color content, and if
* even a relatively small amount is found, the image will be encoded
* with DCT instead of tiffg4.
* The %lrclear and %tbclear parameters give the number of background
* pixels to be added to the foreground region.
*
* The %quality is the jpeg output quality factor for images stored
* in the pdf. Use 0 for the default value (50), which is satisfactory
* for many purposes. Use 75 for standard jpeq quality; 85-95 are very
* high quality. Allowed values are between 25 and 95.
* The %edgeclean parameter is used to remove edge noise, going from
* 0 (default, no removal) to 15 (maximally aggressive removal).
*
* The %title is the title given to the pdf. Use %title == "none"
* to omit the title.
*
* The pdf output is written to %fileout. It is advisable (but not
* required) to have a '.pdf' extension.
*
* The intent is to use pdftoppm to render the images at 150 pixels/inch
* for a full page, when scalefactor = 1.0. The renderer uses the
* mediaboxes to decide how big to make the images. If those boxes
* have values that are too large, the intermediate ppm images can
* be very large. To prevent that, we compute the resolution to input
* to pdftoppm that results in RGB ppm images representing page images
* at about 150 ppi (when scalefactor = 1.0). These images are about
* 6MB, but are written quickly because there is no compression.
* As the first step in processing, images are saved in the ./image
* directory as RGB at 300 ppi in ppm format. Each image is about 26MB.
* Delete those images after use.
*
* N.B. This requires the Poppler package of pdf utilities, such as
* pdfimages and pdftoppm. For non-unix systems, this requires
Expand Down Expand Up @@ -123,21 +91,20 @@ l_int32 main(int argc,
char buf[256];
char *basedir, *fname, *tail, *basename, *imagedir, *title, *fileout;
l_int32 threshold, lrclear, tbclear, edgeclean, lradd, tbadd;
l_int32 render_res, onebit, savecolor, i, n, ret;
l_float32 scalefactor;
l_int32 render_res, i, n, ret;
SARRAY *sa;

if (argc != 10)
return ERROR_INT(
"Syntax: croppdf basedir threshold lrclean tbclear edgeclean "
"Syntax: croppdf basedir threshold lrclear tbclear edgeclean "
"lradd tbadd title fileout", __func__, 1);
basedir = argv[1];
threshold = atoi(argv[2]);
lrclear = atoi(argv[3]); /* set to 1 to enforce 1 bpp tiffg4 encoding */
tbclear = atoi(argv[4]); /* set to 1 to enforce 1 bpp tiffg4 encoding */
edgeclean = atoi(argv[5]); /* jpeg quality */
lradd = atoi(argv[6]); /* set to 1 to enforce 1 bpp tiffg4 encoding */
tbadd = atoi(argv[7]); /* set to 1 to enforce 1 bpp tiffg4 encoding */
lrclear = atoi(argv[3]);
tbclear = atoi(argv[4]);
edgeclean = atoi(argv[5]);
lradd = atoi(argv[6]);
tbadd = atoi(argv[7]);
title = argv[8];
fileout = argv[9];
setLeptDebugOK(1);
Expand Down Expand Up @@ -184,17 +151,13 @@ SARRAY *sa;
}
sarrayDestroy(&sa);

/* Optionally binarize, then scale and collect all images in memory.
* If n > 100, use pixacomp instead of pixa to store everything
* before generating the pdf.
* When using the onebit option, It is important to binarize
* the images in leptonica. Do not let 'pdftoppm -mono' do
* the binarization, because it will apply error-diffusion
* dithering to gray and color images. */
/* Process each image and collect all resulting 1 bpp images
* in memory. If n > 200, use pixacomp instead of pixa to
* store the images before generating the pdf. */
sa = getSortedPathnamesInDirectory(imagedir, NULL, 0, 0);
lept_free(imagedir);
sarrayWriteStderr(sa);
lept_stderr("compressing ...\n");
lept_stderr("croping ...\n");
cropFilesToPdf(sa, threshold, lrclear, tbclear, edgeclean,
lradd, tbadd, title, fileout);

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46 changes: 17 additions & 29 deletions src/pdfapp.c
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Expand Up @@ -231,41 +231,29 @@ PIXAC *pixac1 = NULL;
* \brief cropFilesToPdf()
*
* \param[in] sa sorted full pathnames of images
* \param[in] threshold set to 1 to enforce 1 bpp tiffg4 encoding
* \param[in] lr_clear set to 1 to enforce 1 bpp tiffg4 encoding
* \param[in] tb_clear if %onebit == 1, set to 1 to save color
* \param[in] edgeclean scaling factor applied to each image; > 0.0
* \param[in] lr_add for jpeg: 0 for default (50; otherwise 25 - 95.
* \param[in] tb_add for jpeg: 0 for default (50; otherwise 25 - 95.
* \param[in] threshold threshold for binarization
* \param[in] lr_clear full res pixels cleared at left and right sides
* \param[in] tb_clear full res pixels cleared at top and bottom sides
* \param[in] edgeclean parameter for removing edge noise (0-15)
* default = 0 (no removal);
* \param[in] lr_add full res expansion of crop box on left and right
* \param[in] tb_add full res expansion of crop box on top and bottom
* \param[in] title [optional] pdf title; can be null
* \param[in] fileout pdf file of all images
* \return 0 if OK, 1 on error
*
* <pre>
* Notes:
* (1) This function is designed to optionally scale and compress a set of
* images, wrapping them in a pdf in the order given in the input %sa.
* (2) It does the image processing for prog/compresspdf.c.
* (3) Images in the output pdf are encoded with either tiffg4 or jpeg (DCT),
* or a mixture of them depending on parameters %onebit and %savecolor.
* (4) Parameters %onebit and %savecolor work as follows:
* %onebit = 0: no depth conversion, default encoding depends on depth
* %onebit = 1, %savecolor = 0: all images converted to 1 bpp
* %onebit = 1, %savecolor = 1: images without color are converted
* to 1 bpp; images with color have the color preserved.
* (5) In use, if most of the pages are 1 bpp but some have color that needs
* to be preserved, %onebit and %savecolor should both be 1. This
* causes DCT compression of color images and tiffg4 compression
* of monochrome images.
* (6) The images will be concatenated in the order given in %sa.
* (7) The scalefactor is applied to each image before encoding.
* If you enter a value <= 0.0, it will be set to 1.0.
* (8) Default jpeg quality is 50; otherwise, quality factors between
* 25 and 95 are enforced.
* (9) Page images at 300 ppi are about 8 Mpixels. RGB(A) rasters are
* then about 32 MB (1 bpp images are about 1 MB). If there are
* more than 25 images, store the images after processing as an
* array of compressed images (a Pixac); otherwise, use a Pixa.
* (1) This function is designed to optionally remove white space from
* around the page images, and generate a pdf that prints with
* foreground occupying much of the full page.
* (2) It does the image processing for prog/croppdf.c.
* (3) Images in the output pdf are 1 bpp and encoded with tiffg4.
* (4) See documentation in pixCropImage() for details on the processing.
* (5) The images will be concatenated in the order given in %sa.
* (6) Page images at 300 ppi are about 1 Mpixels. We allow up to 200
* uncompressed rasters to be stored in memory. If more than 200
* pages, the stored images are compressed with tiffg4.
* </pre>
*/
l_ok
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