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LuisG72
Posts: 36
Posted 11:04 Apr 21, 2020 |

Are the RGB Planes sizes 8x8 pixels in size?

yzhao52
Posts: 32
Posted 11:34 Apr 21, 2020 |

R/G/B plane sizes shall be multiple of 8 since the DCT-based coding requires 8x8 blocks. For example, if the input color image is 50x60, the extracted R/G/B planes shall be 56x64.

The Y/Cb/Cr in 444 format shall be the same size as R/G/B, i.e. 56x64. However, for Cb/Cr in 420 format, their sizes shall be 32x32 (not 28x32!) because Cb/Cr's DCT and Quantization are conducted in 8x8 blocks in the 420 resolution.

Last edited by yzhao52 at 11:36 Apr 21, 2020.
LuisG72
Posts: 36
Posted 12:28 Apr 22, 2020 |

Ok so just to verify and I understand this correctly. 1 RGB plane is a block of 8x8 Pixels (64 pixels) in an image of 50x60 we increase the size to be a multiple of 8 to 56x64. So in the 56x64 image, there would be 56 RGB planes?

yzhao52
Posts: 32
Posted 15:21 Apr 22, 2020 |

That's not the correct understanding. For one color image, each pixel has three components, R, G, and B. Many times, we'd like to work on all R values of one image, which is one 2-D array; and we call this the R plane. Similarly, we have G, B planes.

In our example, the padded image becomes 56x64, and each plane is 56x64 2-D array.