Espaços de representação de cores


Quando falamos em colocar cores em objetos ou em uma cena logo nos vem à mente o padrão que nos foi apresentado quando crianças, de amarelo, vermelho, roxo, entretanto a representação de todas as cores para fins computacionais tem que ser quantizada e discretizada de alguma maneira para que todas as cores possam ser “formadas” por alguma combinação ou formula, armazenando o mínimo possível de informação.

Tal esforço resulta nos espaços de representação de cores, que nada mais são do que abstrações das cores para alguma forma matematicamente representável como um vetor de valores. Nesse post vou apresentar os dois mais conhecidos e aceitos pela comunidade de computação gráfica.

Espaço RGB

O modelo de espaço de cores RGB é provavelmente o mais usado entre os modelos de cores,
especialmente para dados de 8 bits. A teoria do espaço de RGB, de Thomas Young (1773-
1829), é baseada no princípio de que diversos efeitos cromáticos são obtidos pela projeção da
luz branca através dos filtros vermelho, verde e azul e pela superposição de círculos nas cores
projetadas. Conforme descrito em (UFRGS, 2010)
O espa¸co de cores RGB é tradicionalmente representado através de uma figura geométrica
denominada de ”cubo das cores”, apresentado na Figura

O espaço RGB é o padrão adotado pelo atual paradigma de computação gráfica. Um
detalhe a se considerar é que ao calcular as cores nas equações de iluminação usa-se o espaço
RGB ideal, entretanto ao desenhar um pixel na tela o adotado é o RBG do monitor que é
ligeiramente diferente. O sistema RGB não é linear.

 

Espaço HSV

Um outro espa¸co importante é o H(ue) S(aturation)V(alue) que representa o espaço de cores de
forma mais intuitiva do que o RBG (uma tripla de cores). O sistema HSV é uma transformação
não linear do RGB e tende a representar a sensação que temos das cores. A definição de Munsel
encontrada no livro RealTime Rendering de HOFFMAN, 2008 diz:
 Hue : É a característica que nos leva a distinguir entre famílias de cores, de vermelho
para o amarelo, ou do verde para o azul ou rosa.
 Saturation: É a característica das cores que nos leva a diferenciar entre uma cor forte
ou fraca.
 Value: É a característica das cores que nos leva a distinguir uma cor clara de uma cor
escura.
A idéia do HSV é facilitar a vida dos artistas ao compor cores, uma vez que não é tão
intuitivo pensar em termos de RGB.

 

Direitos

A imagem da palleta foi retirada do site

http://aibesarc2.blogspot.com/2011/02/exemplos-de-modelos-rgb-cmky-hsv-e-yuv.html

 

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