encoding-decoding greyscale

• to media tree , master, commit 8caec72e8cbff65afa38928197bea5a393b67975

• I frist added the patches of debug prints: 0002-dafna-prints.patch

• So, git am 0001-dafna-prints.patch

• Then, a silly patch to support greyscale: git am 0003-greyscale-stupid.patch

• instead of the two above, can add only the grey patch without prints: git am 0001-Basic-support-only-to-greyscale.patch

• compile and install the kernel and modules

• sudo modprobe vicodec

• generate raw greyscale 640x480 image called "lena_grey640_480.ppm.raw" ./generate_lena_raw_grey640x480.sh

• to encode the image: ./v4l2-encode640x480_grey <encoder dev file>

• to decode back to the original: ./v4l2-decode640x480_grey <decoder dev file>

• to plot a raw decoded greyscale image: python3 plot_raw_grey_img.py <img> <width> <height>

• for example python3 plot_raw_grey_img.py lena_grey.raw 640 480

debugging with printing:

sudo su
echo 8 > /proc/sys/kernel/printk

for dynamic debug , as root:

echo "file codec-fwht.c line 1- +p" > /sys/kernel/debug/dynamic_debug/control

• v4l2-decode.c is from https://gitlab.collabora.com/koike/v4l2-codec.git

• constantly keep dmesg logs: tail -f /var/log/kern.log

• 0001-dafna-prints.patch debug prints patch

Video4linux2

I encountered problems compiling the v4l-utils program. I use ubuntu 18.04, I tried to compile with qt4 but I got a compilation error:

qvidcap.cpp:14:10: fatal error: QtMath: No such file or directory
 #include <QtMath>

I think that QtMath is available only on qt5

So I installed qt5 with sudo apt install qtbase5-dev and configured and compiled again (after make clean), This time I got compilation error in moc_qv4l2.cpp, starting with the error:

moc_qv4l2.cpp:13:2: error: #error "This file was generated using the moc from 4.8.7. It"
 #error "This file was generated using the moc from 4.8.7. It"
  ^~~~~

This cpp file is generated with moc and /usr/bin/moc is a symlink to /usr/bin/qtchooser

qtchooser use a conf file to decide which qt to use, apparently the conf file /usr/lib/x86_64-linux-gnu/qt-default/qtchooser/default.conf is a symlink to /usr/share/qtchooser/qt4-x86_64-linux-gnu.conf, So I just changed it:

sudo ln -s -T /usr/share/qtchooser/qt5-x86_64-linux-gnu.conf /usr/lib/x86_64-linux-gnu/qt-default/qtchooser/default.conf -f

============== Uvcvideo is the module that creates the /dev/video0 /dev/video1, so removing it also removes those files But it is needed to remove it in order to reinstall videodev since uvcvideo depends on it

Add support for a new pixel format to vicodec

struct v4l2_fwht_pixfmt_info {
        u32 id;
        //used to calc `pix->bytesperline = q_data->width * info->bytesperline_mult;`
        unsigned int bytesperline_mult;
        //used to calculate the `pix->sizeimage` in the function `vidioc_try_fmt`, pix is pixel format from the uapi
        //also set `ctx->q_data[V4L2_M2M_SRC].sizeimage` in `vicodec_open`
        unsigned int sizeimage_mult;
        unsigned int sizeimage_div;
        
        unsigned int luma_step; //param `input_step` for the `encode_plane` func in ./codec-fwht.c
        unsigned int chroma_step; ///param `input_step` for the `encode_plane` func in ./codec-fwht.c
        /* Chroma plane subsampling */
        unsigned int width_div;
        unsigned int height_div;
};

From the uapi:

/*
 *	V I D E O   I M A G E   F O R M A T
 */
struct v4l2_pix_format {
	__u32			width;
	__u32			height;
	__u32			pixelformat;
	__u32			field;		/* enum v4l2_field */
	__u32			bytesperline;	/* for padding, zero if unused */
	__u32			sizeimage;
	__u32			colorspace;	/* enum v4l2_colorspace */
	__u32			priv;		/* private data, depends on pixelformat */
	__u32			flags;		/* format flags (V4L2_PIX_FMT_FLAG_*) */
	union {
		/* enum v4l2_ycbcr_encoding */
		__u32			ycbcr_enc;
		/* enum v4l2_hsv_encoding */
		__u32			hsv_enc;
	};
	__u32			quantization;	/* enum v4l2_quantization */
	__u32			xfer_func;	/* enum v4l2_xfer_func */
};

and in vicodec-core.c: This struct does not seem to be used

struct pixfmt_info {
        u32 id;
        unsigned int bytesperline_mult;
        unsigned int sizeimage_mult;
        unsigned int sizeimage_div;
        unsigned int luma_step;
        unsigned int chroma_step;
        /* Chroma plane subsampling */
        unsigned int width_div;
        unsigned int height_div;
};

perl scripts/checkpatch.pl --types BRACES shows if statements with oneline that has { a multilne one-line will not be detected. Also C99_COMMENTS type suppose to detect // comments but does not work