next up previous contents
Next: 3. The VIPS image Up: 2. The VIPS file Previous: 2.2 Computation formats   Contents

2.3 Storage formats

All storage formats have other values for the Coding field. This release supports only IM_CODING_LABQ format.

IM_CODING_LABQ stores $L^{*}$, $a^{*}$ and $b^{*}$ for each pixel, with 10 bits for $L^{*}$ and 11 bits for each of $a^{*}$ and $b^{*}$. These 32 bits are packed into 4 bytes, with the most significant 8 bits of each value in the first 3 bytes, and the left-over bits packed into the final byte as 2:3:3.

This format is a little awkward to process. Some VIPS functions can work directly on IM_CODING_LABQ images (im_extract(), for example), but most will require you to unpack the image to one of the computation formats (for example with im_LabQ2Lab()) first.


John Cupitt 2004-11-02