<Tr> <Th> Feature description </Th> </Tr> <Tr> <Td> <Ul> <Li> SIFT </Li> <Li> SURF </Li> <Li> GLOH </Li> <Li> HOG </Li> </Ul> </Td> </Tr> <Ul> <Li> SIFT </Li> <Li> SURF </Li> <Li> GLOH </Li> <Li> HOG </Li> </Ul> <Tr> <Th> Scale space </Th> </Tr>

Which of the following is not part of the acronym sift