Hi Mikhail, On Mon, Sep 19, 2022 at 10:01:06AM +0300, Mikhail Rudenko wrote: > > Hi Sakari, > > On 2022-09-19 at 06:40 GMT, Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx> wrote: > > > Hi Mikhail, > > > > On Fri, Sep 16, 2022 at 12:27:42AM +0300, Mikhail Rudenko wrote: > >> > >> Hi Dave, > >> > >> On 2022-09-14 at 10:58 +01, Dave Stevenson <dave.stevenson@xxxxxxxxxxxxxxx> wrote: > >> > Hi Mikhail > >> > > >> > On Sun, 11 Sept 2022 at 21:02, Mikhail Rudenko <mike.rudenko@xxxxxxxxx> wrote: > >> >> > >> >> Hello, > >> >> > >> >> this series implements support for Omnivision OV4689 image > >> >> sensor. The Omnivision OV4689 is a high performance, 1/3-inch, 4 > >> >> megapixel image sensor. Ihis chip supports high frame rate speeds up > >> >> to 90 fps at 2688x1520 resolution. It is programmable through an I2C > >> >> interface, and sensor output is sent via 1/2/4 lane MIPI CSI-2 > >> >> connection. > >> >> > >> >> The driver is based on Rockchip BSP kernel [1]. It implements 4-lane CSI-2 > >> >> and single 2688x1520 @ 30 fps mode. The driver was tested on Rockchip > >> >> 3399-based FriendlyElec NanoPi M4 board with MCAM400 camera > >> >> module. > >> >> While porting the driver, I stumbled upon two issues: > [snip] > >> >> (2) The original driver exposes analog gain range 0x0 - 0x7ff, but the > >> >> gain is not linear across that range. Instead, it is piecewise linear > >> >> (and discontinuous). 0x0-0xff register values result in 0x-2x gain, > >> >> 0x100-0x1ff to 0x-4x, 0x300-0x3ff to 0x-8x, and 0x700-0x7ff to 0x-16x, > >> >> with more linear segments in between. Rockchip's camera engine code > >> >> chooses one of the above segments depenging on the desired gain > >> >> value. The question is, how should we proceed keeping in mind > >> >> libcamera use case? Should the whole 0x0-0x7ff be exposed as-is and > >> >> libcamera will do the mapping, or the driver will do the mapping > >> >> itself and expose some logical gain units not tied to the actual gain > >> >> register value? Meanwhile, this driver conservatively exposes only > >> >> 0x0-0xf8 gain register range. > >> > > >> > The datasheet linked above says "for the gain formula, please contact > >> > your local OmniVision FAE" :-( > >> > I would assume that the range is from 1x rather than 0x - people > >> > rarely want a totally black image that 0x would give. Or is it ranges > >> > of 1x - 2x, 2x - 4x, 4x - 8x, and 8x - 16x? > >> > >> A picture is worth a thousand words, so I've attached the results of my > >> experimentation with the gain register. They were obtained with Rockchip > >> 3399, with AEC, AGC and black level subtraction disabled. The image was > >> converted from 10-bit RGGB to 8-bit YUV 4:2:0 by the Rockchip ISP. > > > > Based on that it looks like their medication may have been a little too > > strong. > > > > Could this be implemented so that the control value would be linear linear > > but its range would correspond 1x--16x values? > > > > libcamera will be able to cope with that. > > > > According to the following fragment of the Rockchip camera engine sensor > configuration file for ov4689 [1] > > <Linear index="1" type="double" size="[4 7]"> > [1 2 128 0 1 128 255 > 2 4 64 -248 1 376 504 > 4 8 32 -756 1 884 1012 > 8 16 16 -1784 1 1912 2040] > </Linear>, > > it uses gain register value range 128-255 for gain 1x-2x, 376-504 for > gain 2x-4x, 884-1024 for 4x-8x, and 1912-2040 for 8x-16x. Do you suggest > to implement this calculation in the sensor driver and expose some > linear "logical" gain to userspace (ranging, e.g., 128-2048 for gains > 1x-16x)? Yes. This way the user space can somehow work without knowing this special implementation, even though the granularity changes over the range. I guess the granularity would need to be known in libcamera but that's a separate issue. -- Sakari Ailus
