Converting a HyperText Markup Language (HTML) page into a portable network graphics (PNG) file format can be filled with unexpected results. Some methods are very reliable, but also very limited in their use, including using screen captures from an active web browser and then modifying the saved image. Other methods, such as using programs to specifically convert HTML to PNG, might not render the page in the correct way, in the correct resolution or even with all the more complex components loaded. Scripts that are run from a web server to convert HTML to PNG are sometimes very complex or require the installation of specialized libraries that could themselves have bugs that prevent them from working. Knowing what to expect when creating an image of a website can help to speed the process and reduce unwanted results.
The most basic way to convert HTML to PNG is simply to load a website into a web browser and use a screen-capture program to save the image being displayed. This method has good results and is fairly predictable. It also is limited in its use and requires manual processing of every screen capture, meaning updates to any application using the image will need to be updated whenever an HTML document changes. Still, if all else fails, this is a basic working method.
Programs and scripts that automatically convert HTML to PNG might have automation built in, but also have the possibility of being unable to render all the components on a site. Certain staple design elements — such as animations, some style sheet formatting and streaming media — might not be rendered, leaving large holes in the image of the website or incorrect formatting of the page. This can be avoided either by not using dynamic elements or by finding programs that say they will, in fact, render these components.
The quality of the image created when moving from HTML to PNG files also can be an issue. Some mechanisms that improve the images, text and other visual elements of a page are sometimes employed independently of the browser’s rendering module. This means text and images could appear pixilated or off-color. There are few solutions to this problem except to design HTML documents with all image-enhancing software deactivated.
When using automated HTML to PNG converters, it is important to consider which web pages should be saved as image files. Users of a site might be placed at risk if an image of a page is taken as they are entering their user name and password, looking at private messages or entering personal information. Having this type of image act as the thumbnail for a site creates a massive security risk. Pages that might display user information or that can create dynamic information from user input should always be excluded from automated HTML to PNG generation programs.
Especially with automated HTML to PNG convertors, one should be aware of the aspect ratio of the final images. Some programs will attempt to scale a captured website to fit within pre-defined parameters. This could cause the software to take the image of an HTML document and scale it to fit within a rectangular area that is proportioned differently. This can create distorted images that are unusable.