The sh_mobile_ceu_camera driver implements an advanced algorithm, combining scaling and cropping on the client and on the host. Due to its complexity the algorithm deserves separate documentation. Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@xxxxxx> --- I'm having internet problems here, and it seems the first attempt to send this mail failed magically... resending, sorry, if it ends up double on the list. Documentation/video4linux/sh_mobile_ceu_camera.txt | 157 ++++++++++++++++++++ 1 files changed, 157 insertions(+), 0 deletions(-) create mode 100644 Documentation/video4linux/sh_mobile_ceu_camera.txt diff --git a/Documentation/video4linux/sh_mobile_ceu_camera.txt b/Documentation/video4linux/sh_mobile_ceu_camera.txt new file mode 100644 index 0000000..2ae1634 --- /dev/null +++ b/Documentation/video4linux/sh_mobile_ceu_camera.txt @@ -0,0 +1,157 @@ + Cropping and Scaling algorithm, used in the sh_mobile_ceu_camera driver + ======================================================================= + +Terminology +----------- + +sensor scales: horizontal and vertical scales, configured by the sensor driver +host scales: -"- host driver +combined scales: sensor_scale * host_scale + + +Generic scaling / cropping scheme +--------------------------------- + +-1-- +| +-2-- -\ +| --\ +| --\ ++-5-- -\ -- -3-- +| ---\ +| --- -4-- -\ +| -\ +| - -6-- +| +| - -6'- +| -/ +| --- -4'- -/ +| ---/ ++-5'- -/ +| -- -3'- +| --/ +| --/ +-2'- -/ +| +| +-1'- + +Produced by user requests: + +S_CROP(left / top = (5) - (1), width / height = (5') - (5)) +S_FMT(width / height = (6') - (6)) + +Here: + +(1) to (1') - whole max width or height +(1) to (2) - sensor cropped left or top +(2) to (2') - sensor cropped width or height +(3) to (3') - sensor scale +(3) to (4) - CEU cropped left or top +(4) to (4') - CEU cropped width or height +(5) to (5') - reverse sensor scale applied to CEU cropped width or height +(2) to (5) - reverse sensor scale applied to CEU cropped left or top +(6) to (6') - CEU scale - user window + + +S_FMT +----- + +Do not touch input rectangle - it is already optimal. + +1. Calculate current sensor scales: + + scale_s = ((3') - (3)) / ((2') - (2)) + +2. Calculate "effective" input crop (sensor subwindow) - CEU crop scaled back at +current sensor scales onto input window - this is user S_CROP: + + width_u = (5') - (5) = ((4') - (4)) * scale_s + +3. Calculate new combined scales from "effective" input window to requested user +window: + + scale_comb = width_u / ((6') - (6)) + +4. Calculate sensor output window by applying combined scales to real input +window: + + width_s_out = ((2') - (2)) / scale_comb + +5. Apply iterative sensor S_FMT for sensor output window. + + subdev->video_ops->s_fmt(.width = width_s_out) + +6. Retrieve sensor output window (g_fmt) + +7. Calculate new sensor scales: + + scale_s_new = ((3')_new - (3)_new) / ((2') - (2)) + +8. Calculate new CEU crop - apply sensor scales to previously calculated +"effective" crop: + + width_ceu = (4')_new - (4)_new = width_u / scale_s_new + left_ceu = (4)_new - (3)_new = ((5) - (2)) / scale_s_new + +9. Use CEU cropping to crop to the new window: + + ceu_crop(.width = width_ceu, .left = left_ceu) + +10. Use CEU scaling to scale to the requested user window: + + scale_ceu = width_ceu / width + + +S_CROP +------ + +If old scale applied to new crop is invalid produce nearest new scale possible + +1. Calculate current combined scales. + + scale_comb = (((4') - (4)) / ((6') - (6))) * (((2') - (2)) / ((3') - (3))) + +2. Apply iterative sensor S_CROP for new input window. + +3. If old combined scales applied to new crop produce an impossible user window, +adjust scales to produce nearest possible window. + + width_u_out = ((5') - (5)) / scale_comb + + if (width_u_out > max) + scale_comb = ((5') - (5)) / max; + else if (width_u_out < min) + scale_comb = ((5') - (5)) / min; + +4. Issue G_CROP to retrieve actual input window. + +5. Using actual input window and calculated combined scales calculate sensor +target output window. + + width_s_out = ((3') - (3)) = ((2') - (2)) / scale_comb + +6. Apply iterative S_FMT for new sensor target output window. + +7. Issue G_FMT to retrieve the actual sensor output window. + +8. Calculate sensor scales. + + scale_s = ((3') - (3)) / ((2') - (2)) + +9. Calculate sensor output subwindow to be cropped on CEU by applying sensor +scales to the requested window. + + width_ceu = ((5') - (5)) / scale_s + +10. Use CEU cropping for above calculated window. + +11. Calculate CEU scales from sensor scales from results of (10) and user window +from (3) + + scale_ceu = calc_scale(((5') - (5)), &width_u_out) + +12. Apply CEU scales. + +-- +Author: Guennadi Liakhovetski <g.liakhovetski@xxxxxx> -- 1.6.2.4 -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
