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Old 1st August 2016, 16:13   #1  |  Link
asdf013cv
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how to calculate the intra prediction angle?

after reading this, I finally understand what intra prediction is.

Here, I give my knowledge about intra prediction mode 2 and 10.
Name:  yxkvAc0 - Imgur.png
Views: 363
Size:  17.2 KB
Name:  tbfrxzI - Imgur.png
Views: 351
Size:  11.8 KB
So, every sample locations are projected to a single reference row.

However, I don't understand how to calculate special angle, such as 6.
Name:  GoDvOsU - Imgur.png
Views: 354
Size:  11.1 KB
If I use Name:  QK4wNeq - Imgur.png
Views: 356
Size:  65.2 KB, does it mean p is projected to N? (because 14/33 is closer to 2/5 not 3/5.)
Can any one help me how to draw the line or how the formula apply?

Also, I know for some special cases, if the projected pixel indexes is negative, I have to extend the reference row and column.
But, again, how to project the left reference column to the extended reference row?
Name:  3Qi4m4y - Imgur.png
Views: 357
Size:  11.9 KB
(not 23, so the Fig.3 of Intra Coding of the HEVC Standard cannot work here)

Thanks a lot.

Last edited by asdf013cv; 1st August 2016 at 16:31. Reason: change the tag url to IMG
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Old 2nd August 2016, 07:51   #2  |  Link
asdf013cv
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OK.
I think I understand how it works. So I am here to give my answer,
this is intra prediction mode 6 Name:  intra pred 6.png
Views: 336
Size:  21.6 KB.
The color is based on the arrow which is closer to the center of the block.
Am I right?

But I still don't understand the intra prediction mode 22 Name:  intra pred 22.png
Views: 332
Size:  28.3 KB.
Which block is the "?", K or L? And why?
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Old 2nd August 2016, 09:59   #3  |  Link
FancyMouse
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Down to this detail level, you need to read the spec, section 8.4.4.2.6 formula 8-48 extends the reference row by filling the negative indices of the ref row with the column data (AJKL...). For 4x4 mode 22, 8-48 applies just for ref[-1], which calculates to p[-1][1], which would be K.
And don't forget extrapolation (see formula 8-52). Your coloring would not make sense because each predicted sample would depend on 2 pixels in ref array.
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Old 2nd August 2016, 15:55   #4  |  Link
asdf013cv
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Quote:
Originally Posted by FancyMouse View Post
Down to this detail level, you need to read the spec, section 8.4.4.2.6 formula 8-48 extends the reference row by filling the negative indices of the ref row with the column data (AJKL...). For 4x4 mode 22, 8-48 applies just for ref[-1], which calculates to p[-1][1], which would be K.
And don't forget extrapolation (see formula 8-52). Your coloring would not make sense because each predicted sample would depend on 2 pixels in ref array.
Thanks.

However, I have a problem while calculating
Code:
ref[x]=p[-1+x][-1], x=nTbS+1..2*nTbS (8-49)
for nTbS is 4, predModeIntra is 27 and intraPredAngle is 2.

x=4+1..2*4? 8 to 12? How could it be possible.
What is real range for x?
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Old 3rd August 2016, 07:20   #5  |  Link
asdf013cv
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OK.
"nTbS+1..2*nTbS" means "nTbS+1 to 2*nTbS".
if nTbS is 4, then it is "5 to 8".

This is intra prediction 27
Name:  intra pred 27.png
Views: 252
Size:  14.4 KB
The color it not totally true (because the actual extrapolation is (30*B+2*C+16)/32), but the idea is almost correct.
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