Display Histogram is an array of bins and can be generated in many ways
referred to as modes.
Ex: HSV max(RGB), Wighted RGB etc.
Understanding the histogram data format(Ex: HSV max(RGB))
Histogram is just the pixel count.
For a maximum resolution of 10k (10240 x 4320 = 44236800)
25 bits should be sufficient to represent this along with a buffer of 7
bits(future use) u32 is being considered.
max(RGB) can be 255 i.e 0xFF 8 bit, considering the most significant 5
bits, hence 32 bins.
Below mentioned algorithm illustrates the histogram generation in
hardware.
hist[32] = {0};
for (i = 0; i < resolution; i++) {
bin = max(RGB[i]);
bin = bin >> 3; /* consider the most significant bits */
hist[bin]++;
}
If the entire image is Red color then max(255,0,0) is 255 so the pixel
count of each pixels will be placed in the last bin. Hence except
hist[31] all other bins will have a value zero.
Generated histogram in this case would be hist[32] = {0,0,....44236800}
Description of the structures, properties defined are documented in the
header file include/uapi/drm/drm_mode.h
Signed-off-by: Arun R Murthy <arun.r.murthy@xxxxxxxxx>
---
include/uapi/drm/drm_mode.h | 59 +++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 59 insertions(+)
diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
index c082810c08a8b234ef2672ecf54fc8c05ddc2bd3..7a7039381142bb5dba269bdaec42c18be34e2d05 100644
--- a/include/uapi/drm/drm_mode.h
+++ b/include/uapi/drm/drm_mode.h
@@ -1355,6 +1355,65 @@ struct drm_mode_closefb {
__u32 pad;
};
+/*
+ * Maximum resolution at present 10k, 10240x4320 = 44236800
+ * can be denoted in 25bits. With an additional 7 bits in buffer each bin
+ * can be a u32 value.
+ * Maximum value of max(RGB) is 255, so max 255 bins.
+ * If the most significant 5 bits are considered, then bins = 0xff >> 3
+ * will be 32 bins.
+ * For illustration consider a full RED image of 10k resolution considering all
+ * 8 bits histogram would look like hist[255] = {0,0,....44236800}
+ */
+#define DRM_MODE_HISTOGRAM_HSV_MAX_RGB (1 << 0)
+
+/**
+ * struct drm_histogram_caps
+ *
+ * @histogram_mode: histogram generation modes, defined in the above macros
+ * @bins_count: number of bins for a chosen histogram mode. For illustration
+ * refer the above defined histogram mode.
+ */
+struct drm_histogram_caps {
+ u8 histogram_mode;
+ u32 bins_count;
+};
+
+/**
+ * struct drm_histogram_config
+ *
+ * @enable: flag to enable/disable histogram
+ * @hist_mode: histogram mode(HSV max(RGB), RGB, LUMA etc)
+ * @reserved1: Reserved for future use
+ * @reserved2: Reserved for future use
+ * @reserved3: Reserved for future use
+ * @reserved4: Reserved for future use
+ */
+struct drm_histogram_config {
+ bool enable;
+ u8 hist_mode;
+ u32 reserved1;
+ u32 reserved2;
+ u32 reserved3;
+ u32 reserved4;
+};
+
+/**
+ * struct drm_histogram
+ *
+ * @config: histogram configuration data pointed by struct drm_histogram_config
+ * @data_ptr: pointer to the array of histogram.
+ * Histogram is an array of bins. Data format for each bin depends
+ * on the histogram mode. Refer to the above histogram modes for
+ * more information.
+ * @nr_elements: number of bins in the histogram.
+ */
+struct drm_histogram {
+ struct drm_histogram_config config;
+ __u64 data_ptr;
+ __u32 nr_elements;
+};
+
#if defined(__cplusplus)
}
#endif
--
2.25.1
