Does anybody know the difference between GL_UNSIGNED_SHORT_4_4_4_4 and GL_UNSIGNED_SHORT_5_6_5 data types in OpenGL ES?
2
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3 Answers
6
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They are both 16 bit textures.
When using 32 bit texture you have 8 bit for each of the color components plus 8 bit for alpha, maximum quality and alpha control, so 8888.
With 16 bit there's always a compromise, if you only need color and not alpha then use the 565. Why 565 ? Because 16 bits can't divide evenly by 3 and our eyes are better at seing in the green spectrum, so better quality by giving the leftover bit to green. If you need alpha but your images don't use gradients in alpha use 5551, 5 bits for each color 1 bit for alpha. If you image has some gradient alpha then you can can use 4444, 4 bits for each color and 4 bits for alpha.
4444 has the worst color quality but it retains some alpha to mix, I use this for my font textures, for example, lighter than 32 bit and since the fonts are monocromatic they fit well in 4 bits.
4
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I am not an OpenGL expert but :
GL_UNSIGNED_SHORT_4_4_4_4 stands for GL_UNSIGNED_SHORT_R_G_B_A where each RGBA values can have a value of 4 bit each (well that is 2^4)
GL_UNSIGNED_SHORT_5_6_5 stands for GL_UNSIGNED_SHORT_R_G_B. You can see that their is no Alpha value available here so that is a major difference. RGB values can also have greater values since they are 5 6 and 5 bits respectively.
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Well, when using GL_UNSIGNED_SHORT_4_4_4_4 as type in a pixel specification command (glTexImage2D or glReadPixels), the data is assumed to be laid out in system memory as one 16bit value per-pixel, with individual components each taking up 4 consecutive bits. It can only be used with a format of GL_RGBA.
Whereas GL_UNSIGNED_SHORT_5_6_5 also assumes individual pixels as 16bit values, but with the red and blue components taking up 5 bits each and the green component having 6 bits (there is no alpha channel). It can only be used with a format of GL_RGB.
