STRUCT RPPX1_HIST_PARAMS(9)

🌸 NAME 🌸

okay bestie, welcome to the Kernel API Manual page for struct rppx1_hist_params(9) — it's literally the Histogram measurement configuration struct, and it's iconic. this is where the histogram measurement setup lives 💖

---

🦋 SYNOPSIS 🦋

       struct rppx1_hist_params {
           struct v4l2_isp_params_block_header header;
           struct rppx1_window wnd;
           __u32 last_line;
           __u32 v_stepsize;
           __u32 h_step_inc;
           __u32 sample_offs;
           __u8 mode;
           __u8 channel_sel;
           __u8 weights[RPPX1_HIST_WEIGHT_GRIDS_SIZE];
           __u8 coeff[3];
           __u8 sample_shift;
           __u8 reserved;
        };

---

🎀 Members 🎀

• header — block header (type = RPPX1_PARAMS_BLOCK_TYPE_HIST_PRE1, type = RPPX1_PARAMS_BLOCK_TYPE_HIST_PRE2 or type = RPPX1_PARAMS_BLOCK_TYPE_HIST_POST). the little label that says which histogram block this is ✨
• wnd — measurement window coordinates. where the measuring happens, bestie 🎀
• last_line — line number for which the histogram measurement completes. the finish line, fr fr 🏁
• v_stepsize — vertical subsampling divider, 7 bits.
• h_step_inc — horizontal subsampling step counter, 17 bits.
• sample_offs — sample offset, 24 bits.
• mode — histogram measurement mode (from enum rppx1_hist_mode). mode vibes 🌈
• channel_sel — histogram measurement point (see enum rppx1_meas_chan). pick your measurement point 🦋
• weights — weighting factors for each sub-window (5x5 grid). yes, a whole 5x5 grid ✨
• coeff — R-G-B coefficients, 8 bits unsigned Q1.7.
• sample_shift — sample shift, 4 bits.
• reserved — padding.

---

💜 Description 💜

okay so, the RPP-X1 Histogram measurement unit is available on the PRE1, PRE2 and MAIN_POST pipes. Userspace selects which pipe to operate by setting the header.type field to RPPX1_PARAMS_BLOCK_TYPE_HIST_PRE1, RPPX1_PARAMS_BLOCK_TYPE_HIST_PRE2 or RPPX1_PARAMS_BLOCK_TYPE_HIST_POST 💅

The histogram measurement point is selected using the channel field while histogram measurement mode is selected using the mode field. iykyk 👑

Histogram measurement is performed by programming subsampling factors using the v_stepsize and h_step_inc fields and by weighted windowing, by programming the size of the measurement window wnd with weights associated to each cell of the 5x5 measurement grid. Weights are represented as 5 bits integer values ranging from 0 to 16. numbers bestie, exact numbers 🔥

The last_line field controls when the histogram measurement completes. It is usually programmed to the value of (wnd.v_offs + wnd.v_size - 1). that's the little formula right there 🎀

Histogram values are calculated by applying a per-color channel coefficient represented as an 8 bits unsigned Q1.7 integer value. The sample_offs and sample_shift fields allow to reduce the color dynamic range on which histogram data are produced. dynamic range says hi 🌸

---

🔥 SEE ALSO 🔥

• Kernel file ./include/uapi/linux/media/dreamchip/rppx1-config.h
• struct rppx1_window(9)
• enum rppx1_meas_chan(9)
• enum rppx1_params_block_type(9)
• enum rppx1_wbmeas_mode(9)
• struct rppx1_wbmeas_params(9)
• struct rppx1_awbg_params(9)
• enum rppx1_exm_mode(9)
• struct rppx1_exm_params(9)
• enum rppx1_hist_mode(9)
• struct rppx1_bls_fixed(9)
• enum rppx1_bls_mode(9)
• enum rppx1_bls_win_en(9)
• struct rppx1_bls_params(9)
• struct rppx1_ccor_params(9)
• struct rppx1_lsc_params(9)
• enum rppx1_ga_seg_mode(9)
• struct rppx1_ga_params(9)
• struct rppx1_lin_params(9)
• RPPX1_PARAMS_MAX_SIZE(9)
• enum rppx1_stats_block_type(9)
• struct rppx1_wbmeas_stats(9)
• struct rppx1_exm_stats(9)
• struct rppx1_hist_stats(9)
• RPPX1_STATS_MAX_SIZE(9)

---

xoxo, your kernel bestie 🫶 — source/version ./include/uapi/linux/media/dre..., dated October 2026, for the Kernel API Manual page struct rppx1_hist_params(9) 💅