CODEWITHSUNDEEP
javaandroidc++java-native-interfacenative
yanisk
yanisk

Reputation: 79

NDK - process RGB value without Alpha from an ARGB_8888 bitmap

I have a processing algo which performs well if I process each color channel seperately. but when I tried to process the whole pixel value, things missed up. the results are not good. now I want to isolate the 3 color channel from the pixel value( exclude alpha) then work on the new value (the 3 channels). How can I do that in C++? knowing that I tried the RGB_565 bitmap format which is not a good solution. and knowing that I want to merge the RGB into a 24bits variable.

Upvotes: 1

Views: 541

Answers (1)

Sergio
Sergio

Reputation: 8209

You can access each channel separately. The exact way depends on actual pixel format.

ANDROID_BITMAP_FORMAT_RGBA_8888: each pixel is 4-byte long, layout pattern is RGBARGBA..., i.e. the 1-st pixel byte is red component, the 2-d is green, the 3-d is blue and the 4-th is alpha component.

ANDROID_BITMAP_FORMAT_RGB_565: each pixel is 2-byte long, stored in native endianness, so color components may be extracted in next way:

red   = (u16_pix >> 11) & 0x1f;
green = (u16_pix >>  5) & 0x3f;
blue  = (u16_pix >>  0) & 0x1f;

ANDROID_BITMAP_FORMAT_RGBA_4444: is deprecated because of poor quality, you shouldn't even think about this one

ANDROID_BITMAP_FORMAT_A_8: is 1 byte per pixel and designed for alpha-only or grayscale images. It is probably not what you are looking for.

Note that Android has no 24bpp format, and you must choose 32bpp or 16bpp one. About your algo: there are two alternatives - code may access individual components right inside packed pixel value, or you may deinterleave packed pixels into few planes, i.e. arrays, each of them will hold only one channel. Then after processing you may interleave them again to one of the supported formats or transform to some other format you are interested in.

Upvotes: 2

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