ImageGear for C and C++ on Windows v19.10 - Updated
Extra Channel Information
User Guide > How to Work with... > Color > Spot and Mask Channels > Extra Channel Information
This topic provides information about extra channel information:

Extra Color Space

An image may contain multiple Extra channels. An Extra channel can belong to one of the following subtypes: Mask, Spot, or Unknown. These channels can be mixed in arbitrary order. ImageGear does not use separate bitmasks from enumIGColorSpaceIDs for Mask and Spot channels. Instead, it uses IG_COLOR_SPACE_ID_Ex bitmask to specify presence of any of these channels in an image.

ImageGear stores an array of extra channel info objects in the DIB. Length of this array must always be equal to the number of extra channels in the DIB. DIB constructors, color space, and channel manipulation functions must ensure this.

Spot color, Mask, and Extra channels can be appended after any regular color channels, in any order, including color spaces that contain an Alpha or Pre-multiplied Alpha channel.

Reader, Writer and Format Converter

ImageGear can load extra channels from TIFF and PSD file formats. The extra channels are internally stored as specified above and saved back as extra channels when the output format is either TIFF or PSD. Spot color support is added to the raster color conversion mechanism, so when saving an image to a format that doesn't support extra channels, the image spot channels are blended to the base channels. The alpha channels are skipped in this case.