How to solve the problem of horizontal line or horizontal bar printing djvu files with Adobe PDF

After the djvu file is printed in PDF format, the images on each page are divided into many lines, so that the horizontal line (black) appears when printed with a printer ), you can convert the image to PNG before printing it.

Check whether a horizontal line (black) appears. If yes, it may also be printed.

The solution is to print the file on another device instead of the Adobe PDF printer, such as office document image writer, and select
Advanced: Select MDI as the output format. (If tiff is selected, the maximum resolution is 300 dpi, which is poor for photo printing ). Then use the Adobe PDF printer.
Convert to a PDF file. However, each page is still divided into many lines, but when Save as is PNG, there will be no black horizontal line, and then the PNG file on each page will be merged into a PDF file,
In this way, each page is a graph, and the generated PNG file can view its bit depth through attributes, because when it is converted from PNG to PDF, the original seemingly monochrome image will be compressed by JPEG, resulting in
Black, white, and clear. The solution is to set "convert to PDF" in preferences of Acrobat, and change the color compression method of PNG from jpeg
Zip, of course, you can also change grayscal compression to zip, so that when a PNG image with a seemingly monochrome bit depth of 24 is converted into a PDF, there will be no virtual shadows, but black and white are clearly defined.

Another way is to use a printer in Linux to print djvu into a PS or PDF file. At this time, every page in PS or PDF is not one by one, you can use the tool-> advanced editing-> touchup object tool in the acrobat menu to test the settings.

In addition, you can use imread and imwrite in MATLAB to process the generated graphic files and cut off the large margin for printing. The algorithm is simple, that is, the algorithm moves to the center from the beginning and end of the matrix row and column (corresponding to the four sides). When a row (column) when black appears (less than a threshold value, such as 200 (bit depth is 8), or equal to 0 (bit depth is 1), it is determined to arrive at the text area, record row (column) value. The text area of the original matrix is used to adjust the margin to zero. Of course, you can increase the margin. The advantage of MATLAB processing is that hundreds of pages of books can be processed in batches.