Texas Instruments OMAP36 Series, Техническое справочное руководство

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Camera ISP Functional Description
• Same algorithm in both the horizontal and vertical directions, but with separate initial pixel/phase
values and separate RSZ values.
NOTE: The pixel-input pointer (pip) in the algorithm description, points to pixels, not bytes or shorts
in the memory. The fine-input pointer (fip) points to a 1/256 resolution sub-pixel position. The
coarse-input point (cip) points to a 1/8 or 1/4 resolution sub-pixel location, depending on the
number of phases.
6.4.7.2.5.3 Camera ISP VPBE Resizer Horizontal Resizing With Interleaved Chroma
Chroma inputs, Cb and Cr, are 8-bit unsigned values that represent 128-biased 8-bit signed values (the
signed chroma are called U and V instead of Cb and Cr). During the resizing computation, the chroma
values have the 128 bias subtracted to convert to the 8-bit signed format. After vertical resizing, the 128
bias is added back to convert back to 8-bit unsigned format.
Chroma components, which are 2:1 horizontally downsampled with respect to luma, have two methods of
horizontal resizing processing: filtering with luma, and bilinear interpolation.
The horizontal resizing with interleaved chroma option can be selected in the RSZ_CNT [29] CBILIN field
independently of the RSZ_CNT [22:20] HSTPH parameters. However, filtering with luma is intended only
for downsampling, and bilinear interpolation is intended only for upsampling.
For horizontal resizing of Y/Cb/Cr in a combined filtering flow, the algorithm is modified as shown in the
following algorithm descriptions:
Filter Chroma With Luma (4-Tap/8-Phase Mode):
For (i=0; i<output_width; i++) { /* output width depends of input width and resizing factors*/
Coarse-input pointer = (fine-input p 16) >> 5 /* Round to nearest phase */
Pixel-input pointer = (coarse-input pointer >> 3) + 1 /* Round up to a whole pixel */
Coefficient phase = pixel-input pointer & 7 /* 3 LSB = phase */
if (i & 1 == 0) { /* even output pixel, generate YCbCr */
Yout = dot product of the 4 coefficients and the 4 Y inputs starting with pixel-input pointer
Cbout = dot product of the 4 coefficients and the 4 upsampled Cb inputs starting with
pixel-input pointer
Crout = dot product of the 4 coefficients and the 4 upsampled Cr inputs starting with
pixel-input pointer
Clip outputs to 8-bit unsigned for luma, 8-bit
signed for chroma
}
Else {/* odd output pixel, generate Y only */
Yout = dot product of the 4 coefficients and the 4 Y inputs starting with pixel-input pointer
Clip output to 8-bit unsigned
}
Fine-input pointer = fine-input p ( RSZ_CNT [9:0] HRSZ + 1)
}
}
Filter Chroma With Luma (7-Tap/4-Phase Mode):
1221 SWPU177N – December 2009 – Revised November 2010 Camera Image Signal Processor
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