Compressed

The most common type of fz_image is fz_compressed_image - that is, an image based upon a fz_buffer of data in a standard compressed format, such as JPEG, PNG, TIFF, and others.

With such images, the data is held in a fz_compressed_buffer:

$\begin{lstlisting} typedef struct fz_compressed_buffer_s { fz_compression_params params; fz_buffer *buffer; } fz_compressed_buffer; \end{lstlisting}$

The data is held in the buffer field, and the details of the compression used are given in the params field, of type fz_compression_params:

$\begin{lstlisting} struct fz_compression_params_s { int type; union { struct ... ...; int predictor; int bpc; int early_change; } lzw; } u; }; \end{lstlisting}$

The choice of which of the union clauses is used is made by the type field:

$\begin{lstlisting} enum { FZ_IMAGE_UNKNOWN = 0, \par /* Uncompressed samples */... ... FZ_IMAGE_JXR, FZ_IMAGE_PNG, FZ_IMAGE_PNM, FZ_IMAGE_TIFF, }; \end{lstlisting}$

To determine if a fz_image is a compressed image, call:

$\begin{lstlisting} /* fz_compressed_image_buffer: Retrieve the underlying compr... ... *fz_compressed_image_buffer(fz_context *ctx, fz_image *image); \end{lstlisting}$

The easiest way to tell if an image is a compressed image is to request its underlying buffer. If it returns NULL, you know it is not this sort of image.