Messages in this thread | | | Subject | Re: [PATCH v4 1/4] gpu: ipu-v3: ipu-ic: Rename yuv2rgb encoding matrices | From | Steve Longerbeam <> | Date | Tue, 12 Feb 2019 09:42:08 -0800 |
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On 2/12/19 2:17 AM, Philipp Zabel wrote: > Hi Steve, > > On Mon, 2019-02-11 at 10:24 -0800, Steve Longerbeam wrote: > [...] >> Looking more closely at these coefficients now, I see you are right, >> they are the BT.601 YUV full-range coefficients (Y range 0 to 1, U and V >> range -0.5 to 0.5). Well, not even that -- the coefficients are not >> being scaled to the limited ranges, but the 0.5 offset (128) _is_ being >> added to U/V, but no offset for Y. So it is even more messed up. >> >> Your corrected coefficients and offsets look correct to me: Y >> coefficients scaled to (235 - 16) / 255 and U/V coefficients scaled to >> (240 - 16) / 255, and add the offsets for both Y and U/V. >> >> But what about this "SAT_MODE" field in the IC task parameter memory? > That just controls the saturation. The result after the matrix > multiplication is either saturated to [0..255] or to [16..235]/[16..240] > when converting from the internal representation to the 8 bit output.
By saturation I think you mean clipped to those ranges?
> >> According to the manual the hardware will automatically convert the >> written coefficients to the correct limited ranges. > Where did you get that from? "The final calculation result is limited > according to the SAT_MODE parameter and rounded to 8 bits." I see no > mention of coefficients being modified.
Well, as is often the case with this manual, I was interpreting based on poorly written information. By "final calculation result is limited according to the SAT_MODE parameter" I interpreted that to mean the hardware enables scaling from full range to limited range. But I concede that it more likely means it clips the output to those ranges.
> >> I see there is a "sat" field defined in the struct but is not being >> set in the tables. >> >> So what should we do, define the full range coefficients, and make use >> of SAT_MODE h/w feature, or scale/offset the coefficients ourselves and >> not use SAT_MODE? I'm inclined to do the former. > SAT_MODE should be set for conversions to YUV limited range so that the > coefficients can be rounded to the closest value.
Well, we have already rounded the coefficients to the nearest int in the tables. Do you mean the final result (coeff * color component + offset) is rounded?
> Otherwise we'd have to > round towards zero, possibly with a larger error, to make sure the > results are inside the valid ranges.
Makes sense, I will turn on that bit for limited range YUV output for v5, so that the final color component result is clipped to limited range and rounded.
Steve
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