What is the difference between IMAGE_INSTALL and IMAGE_FEATURES in Yocto.
I have seen to enable splash screen in Yocto. We need to write the following to local.conf
IMAGE_FEATURES += "splash"
Why can't I use IMAGE_INSTALL here
IMAGE_INSTALL += "splash"
Can anyone please tell me when should I use IMAGE_FEATURES and IMAGE_INSTALL?
You can think of IMAGE_FEATURES (and EXTRA_IMAGE_FEATURES) as a variable containing a list of "switches" (features, selected from a predefined feature list, that depend on the base class of the target image) that tells the build system to automatically append a given set of packages, and/or different package configurations, to the IMAGE_INSTALL variable. Recipes can check (and append) for specific features in this variable in order to change its default configuration/build process accordingly.
Hence, by adding "splash" to IMAGE_FEATURES you're telling the build system to add the "psplash" package (by default, you can choose other package to provide this feature by modifying the SPLASH variable) to IMAGE_INSTALL through the FEATURE_PACKAGES_splash = ${SPLASH} statement in poky/meta/classes/image.bbclass.
However, you can directly add "psplash" to IMAGE_INSTALL but it is highly likely that some additional packages relating to the "splash" feature will be misconfigured since they won't notice about it (maybe, this is not a big deal in this case...but it definitely could lead to issues in others). That's why you can't (shouldn't) simply add "splash" to IMAGE_INSTALL (in addition to the fact that there is no pacakge named "splash"); the IMAGE_INSTALL variable just keeps a list of packages to be installed in the target image.
For further information refer to the manual.