6.3 The preview images

preview-image-type

preview-image-creators

preview-gs-image-type-alist

What happens when LaTeX is finished depends on the configuration of preview-image-type. What to do for each of the various settings is specified in the variable preview-image-creators. The options to pass into GhostScript and what Emacs image type to use is specified in preview-gs-image-type-alist.

preview-image-type defaults to png. For this to work, your version of GhostScript needs to support the png16m device. If you are experiencing problems here, you might want to reconfigure gs-image-type-alist or preview-image-type. Reconfiguring preview-image-creators is only necessary for adding additional image types.

Most devices make preview-latex start up a single GhostScript process for the entire preview run (as opposed to one per image) and feed it either sections of a PDF file (if PDFLaTeX was used), or (after running Dvips) sections of a single PostScript file or separate EPS files in sequence for conversion into PNG format which can be displayed much faster by Emacs. Actually, not in sequence but backwards since you are most likely editing at the end of the document. And as an added convenience, any preview that happens to be on-screen is given higher priority so that preview-latex will first cater for the images that are displayed. There are various options customizable concerning aspects of that operation, see the customization group Preview Gs for this.

Another noteworthy setting of preview-image-type is `dvipng': in this case, the `dvipng'will get run on DVI output (see below for PDF). This is in general much faster than Dvips and GhostScript. In that case, the option

preview-dvipng-command

will get run for doing the conversion, and it is expected that

preview-dvipng-image-type

images get produced (`dvipng' might be configured for other image types as well). You will notice that preview-gs-image-type-alist contains an entry for dvipng: this actually has nothing to with `dvipng' itself but specifies the image type and GhostScript device option to use when `dvipng' can't be used. This will obviously be the case for PDF output by PDFLaTeX, but it will also happen if the DVI file contains PostScript specials in which case the affected images will get run through Dvips and GhostScript once `dvipng' finishes.

preview-gs-options

Most interesting to the user perhaps is the setting of this variable. It contains the default antialiasing settings -dTextAlphaBits=4 and -dGraphicsAlphaBits=4. Decreasing those values to 2 or 1 might increase GhostScript's performance if you find it lacking.

Running and feeding GhostScript from preview-latex happens asynchronously again: you can resume editing while the images arrive. While those pretty pictures filling in the blanks on screen tend to make one marvel instead of work, rendering the non-displayed images afterwards will not take away your attention and will eventually guarantee that jumping around in the document will encounter only prerendered images.