Internally, what causes latex.exe to be unable to import *.jpg, *.png, *.pdf directly?
[Tex/LaTex] What causes latex.exe to be unable to import *.jpg, *.png, *.pdf directly
conversiongraphicsjpegpdfpng
Related Solutions
JPEG, PNG and PDF are directly supported by PDF format, then they're supported by xdvipdfmx directly. xetex program reads the image files to determine the bounding boxes and produce a .xdv file, then xdvipdfmx program put the image data to PDF output file.
PDF format does not support PostScript stream, thus EPS files are converted to PDF format and then put into PDF output file. xdvipdfmx calls GhostScript to do the trick.
PSTricks pacakge also calls GhostScript to render the PostScript code. The code needed is in xdvipdfmx.con. Herbert may give more explanations.
LaTeX graphics packages
LaTeX and its graphics packages do not touch the image data. TeX does not even provide the reading of binary data. Thus LaTeX passes the image as file name reference to the driver. Also most of the drivers are not image processing programs. They only move the image data in a form appropriate for the output format. For example, dvips only copies the PostScript file into the output PostScript file. Also pdfTeX often do not need to unpack the image data and can copy the data to the PDF structures. Some PNG files are uncompressed and compressed. But this process does not change the image data.
Driver issues Very view drivers are able to resize an image, AFAIK Acrobat Distiller and GhostScript does some obscure things with images like using JPEG compression for PNG images. I do not know how this can be turned off. The related options given in Ps2pdf.htm seems to have no effect.
But you are using pdflatex that does not change the image data. This can be tested. Take a PNG image and convert it to PPM. Also embed the image in a LaTeX document and run pdflatex. The program pdfimages (xpdf) extract the image in PPM format.
convert image.png image.ppm
pdflatex test.tex
pdfimages test.pdf t
diff t-000.ppm image.ppm
The files t-000.ppm and image.ppm should be identical, if the PPM format
is the same (there is a binary and an ASCII variant).
** Different viewing programs** However the programs to view the images are different. The image viewer and the PDF viewer are usually different programs that uses different methods for viewing. For example, a program might use anti-aliasing, …
Scaling vs. resizing
There are no problems in scaling images in LaTeX independent of its method:
- Option
scale - Options
width,height \scalebox- …
Only the place that the image uses on the page differs, the image data remains the same.
A different term is the resizing of an image. Then the actual number of pixels change. Of course, an image processing program cannot invent missing details if the image is enlarged. It can only use better or worse methods to limit the artefacts of resizing.
Screenshots
Screens have low resolutions comparing to printed media and are usually stupid bitmap images of the pixels on the screen even if the original data were high quality vector data (non-pixel fonts, vector drawings).
Some hints to get better quality:
- In some cases a vector screenshot program might be available, e.g. gtk-vector-screenshot.
- A special case are web pages. They could be converted to PDF by printing or there are programs/sites that perform the conversion. But caution, PDF, especially PDFs from screenshot programs might contain bitmap data instead.
- Higher screen resolution with larger font/symbol settings or using settings for visually impaired people.
- A large monitor helps that allows large windows for the screenshot programs that can only catch the pixels inside the screen.
- And it can make sense to turn off anti-aliasing and similar (ClearType) to get clean pixel data. Thus that a black line is displayed by black pixels and not by many gray levels at its edges. That makes it easier to optimize the image for the final media.
Best Answer
Knuth TeX (the original TeX engine) does not support any image directly. The only thing we can do is to use
\specialcommands to telldvidrivers to deal with image files. When.dvifiles converted to PostScript throughDvipsdriver, PostScript images can be supported; anddvipdfm(x)support pdf/png/jpg format.TeX needs to know the bounding box of imported images. Eps files is typically ASCII texts, and has a meta comment like
Then size of eps images can be rendered by TeX well. However, TeX cannot determine the size of binary image files (JPEG, PNG, etc.) itself, tools such as
extractbb(mainly for dvipdfm) orbmpsize.sty(using pdfTeX) is needed.If
dviis not the output format, modern TeX engines (pdfTeX, XeTeX and LuaTeX) can import binary images well.