In PyQt5, both QLabel and QPlainTextEdit Widgets appear to shrink multiple whitespaces in to one. Say if I set the label text to: "abc abc abc", text shown is "abc abc abc".
Apparently, this is happening because of the default html formatting these widgets are using.
Is there a way to set these widgets to show the original text with multiple spaces keeping the original formatting ?
Edit:
QLabel- I was able to get this sorted by introducing <pre> tags. Can anyone help with the QPlainTextEdit ?
The QPlainTextEdit class does not reduce multiple whitespace, and it does not support html at all (as is suggested by the name). The QLabel class also does not reduce multiple whitespace unless you explicitly include html tags (and if you can't avoid that, you can simply use <pre> tags where necessary).
However, I suspect you may be using a variable-width font that has relatively narrow space characters, so the apparent whitespace reduction is actually illusory. If you use a fixed-width font instead, the illusion should disappear.
Related
I've got a QTextDocument read from an HTML file; given a QString of HTML data named topicFileData, I do topicFileTextDocument.setHtml(topicFileData);. I then want to strip off all of the color information, making the whole document just use the default foreground and background brush. (I do not want to explicitly set the text to be black text on a white background; I want to remove the color information from the document.) (Background info: the reason I need to do this is that there are spans within the document that are erroneously set with a black foreground color, rather than just having no color information set, and that causes those spans to display as black-on-black when my app is running in "dark mode", when Qt changes the default text background brush to be black instead of white.)
Here's what I tried:
QTextCursor tc(&topicFileTextDocument);
tc.select(QTextCursor::Document);
QTextCharFormat noColorFormat;
noColorFormat.clearForeground();
noColorFormat.clearBackground();
tc.mergeCharFormat(noColorFormat);
This does not work, unfortunately; it looks like mergeCharFormat() does not understand that I want the clearForeground() and clearBackground() actions to be merged in to strip off those attributes.
I can do tc.setCharFormat(noColorFormat); instead, of course, and that does strip off the color attributes correctly; but it also obliterates all of the other character format info (font, etc.), which is not acceptable.
So, ideally I'd like to find an API that lets me explicitly remove a given text attribute from a QTextDocument. Alternatively, I guess I need to loop through all the spans of the QTextDocument one by one, get the char format of the current span, remove the color attributes from the format, and set the modified format back onto the span. That would be fine; but I have no idea how to loop over spans in that way. Thanks for any help.
Instead of creating a new instance of QTextCharFormat, update the current format and reapply it on the QTextEdit;
default = QTextCharFormat()
charFormat = self.textCursor().charFormat()
charFormat.setBackground(default.background())
charFormat.setForeground(default.foreground())
self.textCursor().mergeCharFormat(charFormat)
A sub-optimal solution that I have found as a workaround is to actually edit the HTML data string before I create the QTextDocument, using a regex:
topicFileData.replace(QRegularExpression("(;? ?color: ?#[0-9a-f][0-9a-f][0-9a-f][0-9a-f][0-9a-f][0-9a-f])"), "");
This works for my situation, because all of the colors in my HTML file are set with color: #XXXXXX style attributes that can be stripped out of the HTML itself. This is fragile, however; colors specified in other ways would not be stripped, and if the body text of the HTML document happened to contain text that matched the regex, the regex would modify it and thus corrupt the content of the document. So I don't recommend this solution, and I won't be accepting it. If somebody can offer a better solution that would be preferable.
I needed to convert some PDF back to text. I tried many soft and online tools and result was always mediocre.
Why is it so difficult technically speaking ?
Let's not assume you are talking about PDFs which merely wrap some bitmap image because it should be clear that in that case you can only resort to OCR with all its restrictions.
Let's instead assume that text is drawn in the PDF at hand.
What is drawn on a PDF page is determined by a sequence of instructions in the content stream of that page. "Text is drawn" on a page means that among those instructions there are some setting the font to use by the instructions to come, some setting the text position and direction to use by the instructions to come, and some actually drawing text given by "string arguments".
Text extraction is the task of taking the sequence of instructions from a content stream and instead of drawing the text as indicated by the font and position setting instructions, to export it in a sensible order using a standard encoding, usually the encoding of the character type of the used programming language / platform.
The first problem is to understand the encoding of the string arguments of those text drawing instructions:
each font can have its own encoding; to extract the text one cannot simply ignore everything but the instructions drawing text and concatenate their string contents, you always have to take the current font into account (some extremely simple text extractors ignore this and, therefore, fail pretty often to return something sensible);
there are a large number of predefined encodings, some reminding of encodings you know, e.g. WinAnsiEncoding, many you likely don't know, e.g. Add-RKSJ-H; these encodings may use a constant number of bytes per glyph or they may be mixed-multibyte; so a text extractor must support very many encodings to start with;
encodings also may be completely ad-hoc and arbitrary; in particular in case of embedded subset fonts one often sees ad-hoc encodings generated by dealing out character codes from some starting value whenever one is needed; i.e. the first glyph in a given font used on a page is given the starting value as code, the next, different glyph is given the starting value plus one, the next, different one the starting value plus two, etc; "Hello World" and a starting value of 48 (ASCII value of '0') would result in "01223453627"; these fonts may contain a mapping to Unicode but they are not required to.
The next problem is to make sense out of the order of the strings:
the string drawing instructions may occur in an arbitrary order, e.g "Hello" might be drawn "lo" first, then after moving back "el", then after again moving back "H"; to extract the text one cannot ignore text positioning instructions and simply concatenate text strings, you always have to take the current position into account (some simple text extractors ignore this and, therefore, can fail to return something sensible);
multi-columnar text may present a difficulty, text may be drawn line by line, e.g. first the text of the top line of the first column, then the top line of the second column, then the second line of the first column, then the second line of the second column, etc.; there need not be any hints in the PDF that the text is multi-columnar.
Another problem is to recognize formatting or styling artifacts:
spaces between words need not be created by drawing a space glyph, it may also be done by text position changing instructions; text extractors not trying to recognize gaps created by text positioning instructions may return a result without spaces; on the other hand the same technique can be used to draw adjacent glyphs at an optimal distance, aka kerning; text extractors trying to recognize gaps created by text positioning instructions may falsely return spaces where there should be none;
sometimes selected words are printed s p a c e d o u t for extra emphasis; in the extracted text these gaps might be presented as space characters which automatic postprocessing of the text may see as word separators;
usually for bold text one uses a different, bold font program; if that is not at hand, people sometimes get creative and emulate bold by printing the same text twice with a minute offset; with a slightly larger offset (or a different transformation) and a different color a shadow effect can be emulated; if the text extractor does not try to recognize this, you end up having some duplicate characters in the output.
More problems arise due to incomplete or wrong extra information:
ToUnicode maps of fonts (optional maps from character code to Unicode) may be incomplete or contain errors; there e.g. are many questions here on stack overflow dealing with incorrect ToUnicode maps for Indian writings; the text extraction results reflect these errors;
there even are PDFs with contradictory information, e.g. with an error in the ToUnicode map but the correct information in an ActualText entry; this is used by some PDF creators to allow correct copy&paste from some programs (preferring an ActualText entry in such a situation) while injecting errors in the output of other programs (preferring ToUnicode information then).
Yet another problem arises if you expect the text extractor to extract only text eventually visible in the page:
text may be drawn outside the current clipping area or outside the visible page area; text extractors need to keep these in mind;
text may be drawn using the rendering mode "invisible"; text extractors have to keep an eye on the rendering mode;
text may be drawn using the same color as the background; to recognize this, a text extractor can not only look at the current instruction and a few graphics state details, it has to take into account anything drawn beforehand in the location of the text;
text may be drawn as a clip path; to recognize whether this text is visible in the end, a text extractor must keep track of what is drawn in the text area as long as the clip path is active;
text may be covered by something else later; a text extractor must drop recognized text in such a case; but depending on blend modes and transparency settings these coverings might or might not allow the text to shine through; thus, for a correct result the text extractor must for each glyph keep track of the color its drawn with, the color of the backdrop, and what all those spiffy effects do with those colors later on; and of course, both glyph color and backdrop color can be interesting, e.g. some shading colors; and the color spaces involved may differ, requiring one to convert back and forth between color spaces; and so on.
Furthermore, text may be drawn where text extractors usually don't look:
some tools hide text from text extraction by putting it into a pattern and filling the page area with that pattern;
similarly there are type 3 fonts; each character in a type 3 font is represented by its own content stream; thus, a tool can draw all text in the content stream of a single type 3 font glyph and then draw that glyph on the page.
...
You surely have meanwhile gotten an idea why text extraction results can be less than optimal. And be assured, the list above is not complete, there still are more complications for text extraction.
I have run into a problem with iText 7 where diacritic marks are painted on top of one another instead of stacking properly when multiple marks are used on a single character. Is there a setting that makes them appear correctly, or is this a bug in iText 7? Any help greatly appreciated. This can be observed if you create a text object in your PDF like below. Obviously, replace the relevant bit with an actual font object, rather than than what I have in there.
new Text("ḗ and ṓ are characters that display incorrectly").setFont(<UNICODE COMPATIBLE FONT LIKE CHARIS>);
While Bruno and Benoit correctly pointed out that for advanced typography stuff like stacking diacritical marks you need pdfCalligraph module, there is a workaround you can try at your own risk. If your combinations of base glyph and diacritics are real, meaning they occur in real texts in some languages or some other known contexts, then such combinations are most probably present in Unicode and have their own number associated with them. For instance, in text you provided, they are 0xU1E17 and 0x1E53 Unicode characters. Some fonts may contain such glyphs, so that there is a second option to showing base glyph and stacking diacritics: showing combined glyphs. For example, ArialUni shipped with Windows does contain the above mentioned glyphs.
To try this approach, you would need the following code for composing known Unicode base glyph + diacritics combinations into single glyphs:
String originalStr = "ḗ and ṓ are characters that display incorrectly";
String normalizedStr = java.text.Normalizer.normalize(originalStr, Normalizer.Form.NFC);
new Text(normalizedStr); // Use this normalized Text instance
The result that I got with ArialUni:
But again as I mentioned do it at your own risk because it will only work if there are necessary combinations present both in Unicode and font. For correct rendering you still should use pdfCalligraph.
Say I have a PDF file that contains one or more embedded fonts. Here's my understanding of how a single character of text is rendered:
First, determine which font the character uses.
Use the font's "cmap," embedded in the PDF, to determine the font's glyph name for the given character. For example, the character '&' in PDF text might map to a glyph that the font internally calls 'ampersand'.
Use the font's "glyf" table to determine the bounding box / drawing instructions for the glyph name.
Here's my question: is a PDF cmap generally consistent? Put another way, if I encounter the character "&" in a PDF, can I be assured that the cmap will always map "&" to the ampersand glyph? Or does some PDF-generation software create its own arbitrary mapping between character codes and glyph names (which would be rather evil and possibly break in-PDF searching and text selection)?
Of course I realize it's possible for the cmap to use an unintuitive mapping -- I guess I'm asking, does this actually happen in the Real World?
My specific use-case is in the world of music fonts. I'm analyzing characters in a PDF to determine which music glyph each one represents (e.g., treble clef, notehead, etc.). I want to know how confident I can be that the combination of font name and character code will always result in the same glyph. For example, if I know the font name is "Opus" and the glyph is "#", can I assume that will always be mapped to the treble clef glyph? Or do I have to analyze the glyph's metrics to make sure it's actually a treble clef?
It differs from one PDF creator to another.
A fairly common method (alas!) is "order encountered", where the first character in the text stream gets mapped to \001, the next to \002 and so on. So the text "Hello" would be encoded as \001\002\003\003\004.
I want to know how confident I can be that the combination of font name and character code will always result in the same glyph.
In a single PDF document, if the same font object is used in different contexts, it will be true -- the mapping is defined inside the font object. If you encounter another font object that uses the same font but it points to another font stream (i.e., the font subset is embedded twice), then it may not be true. Each subset may have an encoding of its own.
Only if the font object contains a /ToUnicode mapping, you can be confident that values map to the correct characters.
I have a problem to strip out the format in a note table
Here is an example:
";\red31\green73\blue125;
\viewkind4\uc1\ltrpar\f0\fs20 USEFUL TEXT BODY \cf1\f3
\ltrpar\f0\fs17
"
How to get rid of those stuff? I want to play safe not to replace anything after'\'
Many thanks,
Rick
Your making it quite difficult for yourself by not replace '\' .
If you look at http://other9.tripod.com/Refs/easy-rtf.html you will see that there are different RTF codes and there is no default size for the codes.
Additionally, it is not like HTML where there must be a necessary "closing" tag which makes it additionally difficult.
The only thing I can think of is to record all possible RTF codes (or use an RTF parser library) and hence be able to recognize if a \ is or is not RTF code.