How did the Spanish perceive Native Americans?
This question is difficult to answer without a context; there were many Native Americans that the Spanish encountered in their explorations and conquests throughout the Americas. Certainly the Spanish were not of a single mind when it came to Native Americans. There are those, such as Bartolome de las Casas, who sought to record, expose and fight against the cruelty and inhumanity of the Spanish in regards to their Native subjects. However, the majority opinion, as evidenced by Spanish practices in the colonial period, demonstrate a view that is more in line with that of Juan Gines de Sepulveda:
The Spaniards are perfectly right to govern these barbarians of the New World and adjacent islands; they are in prudence, ingenuity, virtue, and humanity as inferior to the Spaniards as children are to adults and women are to men, there being as much difference between them as that between wild and cruel and very merciful persons, the prodigiously intemperate and the continent and tempered, and I daresay from apes to men.
There are at least two reasons for the predominance of this viewpoint: the "alienness" of the native culture, and the justification of Spanish actions.
The Spanish were, as one might expect of Renaissance Christians, horrified by the human sacrifices that cultures such as the Aztecs practiced not only with regularity, but with the full consent and devotion of their population and social structure. This, perhaps more than anything else, convinced the Spanish that the Native Americans were in dire need of Christian salvation, as only a Satanic influence could have compelled them to sacrifice, let alone consume, human flesh (ignoring the irony that the Eucharist mirrors this act).
Additionally, it was necessary to view the Natives as inferiors in order to justify the continued subjugation and exploitation of them; Spanish dominance could be seen as not only a right, but a salvation, rescuing the savages from the depths of their own ignorance. It may be mincing terms to attempt to distinguish where the fabrication ends and where the genuine belief begins, for in that time period it was perfectly acceptable to view European culture in contrast to all others on a scale of civilization vs. savagery.
So, there is no single "Spanish" perception of the Native Americans, but the majority appear to have viewed them as savages requiring Christian salvation, and/or natural inferiors rightly trampled under the divine authority vested in the Spanish.