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I420 Color Space

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Štěpán Rezek

I420 Color Space

Dear gstreamer developers,
I have got a question regarding I420 color space or, maybe better said, color spaces in gstreamer in general.
I am trying to write a plugin, which will allow to draw anything on video stream using cairo functions. I successfully derived the existing cairotextoverlay plugin and I am changing it to draw anything on cairo surface.
One of the problems I am currently challenging is the I420 color space. The existing cairotextoverlay works in a way that it takes cairo
overlay in ARGB32 color space, translates it into the I420 color space and than blits in to the current video_frame. This is done in function
gst_vector_overlay_push_frame. Everything works fine with one small, but important problem: it translates everything into greyscale, but what I need is to draw colored things on the frame as well.
Is there any obvious solution to this problem, or do I have to learn more about color spaces and program that "translation" myself?

Thank you in advance

The functions (from plugins-good/ext/cairo/gsttextoverlay.c) are:
********************* code ***************************************
static GstFlowReturn gst_vector_overlay_push_frame
(GstCairoVectorOverlay * overlay, GstBuffer * video_frame)
{
guchar *y, *u, *v;

...
video_frame = gst_buffer_make_writable (video_frame);
...

y = GST_BUFFER_DATA (video_frame);
u = y + I420_U_OFFSET (overlay->width, overlay->height);
v = y + I420_V_OFFSET (overlay->width, overlay->height);

...

/* blit text on video image */
gst_vector_overlay_blit_1 (overlay,
y + (ypos / 1) * I420_Y_ROWSTRIDE (overlay->width),
overlay->text_fill_image, 255, I420_Y_ROWSTRIDE (overlay->width));
gst_vector_overlay_blit_sub2x2 (overlay,
u + (ypos / 2) * I420_U_ROWSTRIDE (overlay->width),
overlay->text_fill_image, 128, I420_U_ROWSTRIDE (overlay->width));
gst_vector_overlay_blit_sub2x2 (overlay,
v + (ypos / 2) * I420_V_ROWSTRIDE (overlay->width),
overlay->text_fill_image, 128, I420_V_ROWSTRIDE (overlay->width));

return gst_pad_push (overlay->srcpad, video_frame);
}

***************************** code ends ***********************
where blit functions are

****************************** code ************************

/* These macros are adapted from videotestsrc.c */
#define I420_Y_ROWSTRIDE(width) (GST_ROUND_UP_4(width))
#define I420_U_ROWSTRIDE(width) (GST_ROUND_UP_8(width)/2)
#define I420_V_ROWSTRIDE(width)
((GST_ROUND_UP_8(I420_Y_ROWSTRIDE(width)))/2)

#define I420_Y_OFFSET(w,h) (0)
#define I420_U_OFFSET(w,h)
(I420_Y_OFFSET(w,h)+(I420_Y_ROWSTRIDE(w)*GST_ROUND_UP_2(h)))
#define I420_V_OFFSET(w,h)
(I420_U_OFFSET(w,h)+(I420_U_ROWSTRIDE(w)*GST_ROUND_UP_2(h)/2))

#define I420_SIZE(w,h)
(I420_V_OFFSET(w,h)+(I420_V_ROWSTRIDE(w)*GST_ROUND_UP_2(h)/2))

static inline void gst_vector_overlay_blit_1 (GstCairoVectorOverlay *
overlay, guchar * dest,
guchar * text_image, gint val, guint dest_stride)
{
gint i, j;
gint x, a, y;
gint y0 = 0;

y = val;

for (i = 0; i < overlay->font_height; i++) {
for (j = 0; j < overlay->width; j++) {
x = dest[(i + y0) * dest_stride + j];
a = text_image[4 * (i * overlay->width + j) + 1];
dest[(i + y0) * dest_stride + j] = (y * a + x * (255 - a)) / 255;
}
}
}

static inline void gst_vector_overlay_blit_sub2x2 (GstCairoVectorOverlay
* overlay, guchar * dest,
guchar * text_image, gint val, guint dest_stride)
{
gint i, j;
gint x, a, y;
gint y0 = 0;

y = val;

for (i = 0; i < overlay->font_height; i += 2) {
for (j = 0; j < overlay->width; j += 2) {
x = dest[(i / 2 + y0) * dest_stride + j / 2];
a = (text_image[4 * (i * overlay->width + j) + 1] +
text_image[4 * (i * overlay->width + j + 1) + 1] +
text_image[4 * ((i + 1) * overlay->width + j) + 1] +
text_image[4 * ((i + 1) * overlay->width + j + 1) + 1] + 2) / 4;
dest[(i / 2 + y0) * dest_stride + j / 2] = (y * a + x * (255 - a))
/ 255;
}
}
}

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Dejan Sakelsak

Re: I420 Color Space

check this patches out:

http://bugzilla.gnome.org/show_bug.cgi?id=526670

regards,
Dejan

On 10/26/08, Rezek Štěpán <[hidden email]> wrote:

> Dear gstreamer developers,
> I have got a question regarding I420 color space or, maybe better said, color spaces in gstreamer in general.
> I am trying to write a plugin, which will allow to draw anything on video stream using cairo functions. I successfully derived the existing cairotextoverlay plugin and I am changing it to draw anything on cairo surface.
> One of the problems I am currently challenging is the I420 color space. The existing cairotextoverlay works in a way that it takes cairo
> overlay in ARGB32 color space, translates it into the I420 color space and than blits in to the current video_frame. This is done in function
> gst_vector_overlay_push_frame. Everything works fine with one small, but important problem: it translates everything into greyscale, but what I need is to draw colored things on the frame as well.
> Is there any obvious solution to this problem, or do I have to learn more about color spaces and program that "translation" myself?
>
> Thank you in advance
>
> The functions (from plugins-good/ext/cairo/gsttextoverlay.c) are:
> ********************* code ***************************************
> static GstFlowReturn gst_vector_overlay_push_frame
> (GstCairoVectorOverlay * overlay, GstBuffer * video_frame)
> {
> guchar *y, *u, *v;
>
> ...
> video_frame = gst_buffer_make_writable (video_frame);
> ...
>
> y = GST_BUFFER_DATA (video_frame);
> u = y + I420_U_OFFSET (overlay->width, overlay->height);
> v = y + I420_V_OFFSET (overlay->width, overlay->height);
>
> ...
>
> /* blit text on video image */
> gst_vector_overlay_blit_1 (overlay,
> y + (ypos / 1) * I420_Y_ROWSTRIDE (overlay->width),
> overlay->text_fill_image, 255, I420_Y_ROWSTRIDE (overlay->width));
> gst_vector_overlay_blit_sub2x2 (overlay,
> u + (ypos / 2) * I420_U_ROWSTRIDE (overlay->width),
> overlay->text_fill_image, 128, I420_U_ROWSTRIDE (overlay->width));
> gst_vector_overlay_blit_sub2x2 (overlay,
> v + (ypos / 2) * I420_V_ROWSTRIDE (overlay->width),
> overlay->text_fill_image, 128, I420_V_ROWSTRIDE (overlay->width));
>
> return gst_pad_push (overlay->srcpad, video_frame);
> }
>
> ***************************** code ends ***********************
> where blit functions are
>
> ****************************** code ************************
>
> /* These macros are adapted from videotestsrc.c */
> #define I420_Y_ROWSTRIDE(width) (GST_ROUND_UP_4(width))
> #define I420_U_ROWSTRIDE(width) (GST_ROUND_UP_8(width)/2)
> #define I420_V_ROWSTRIDE(width)
> ((GST_ROUND_UP_8(I420_Y_ROWSTRIDE(width)))/2)
>
> #define I420_Y_OFFSET(w,h) (0)
> #define I420_U_OFFSET(w,h)
> (I420_Y_OFFSET(w,h)+(I420_Y_ROWSTRIDE(w)*GST_ROUND_UP_2(h)))
> #define I420_V_OFFSET(w,h)
> (I420_U_OFFSET(w,h)+(I420_U_ROWSTRIDE(w)*GST_ROUND_UP_2(h)/2))
>
> #define I420_SIZE(w,h)
> (I420_V_OFFSET(w,h)+(I420_V_ROWSTRIDE(w)*GST_ROUND_UP_2(h)/2))
>
>
> static inline void gst_vector_overlay_blit_1 (GstCairoVectorOverlay *
> overlay, guchar * dest,
> guchar * text_image, gint val, guint dest_stride)
> {
> gint i, j;
> gint x, a, y;
> gint y0 = 0;
>
> y = val;
>
> for (i = 0; i < overlay->font_height; i++) {
> for (j = 0; j < overlay->width; j++) {
> x = dest[(i + y0) * dest_stride + j];
> a = text_image[4 * (i * overlay->width + j) + 1];
> dest[(i + y0) * dest_stride + j] = (y * a + x * (255 - a)) / 255;
> }
> }
> }
>
> static inline void gst_vector_overlay_blit_sub2x2 (GstCairoVectorOverlay
> * overlay, guchar * dest,
> guchar * text_image, gint val, guint dest_stride)
> {
> gint i, j;
> gint x, a, y;
> gint y0 = 0;
>
> y = val;
>
> for (i = 0; i < overlay->font_height; i += 2) {
> for (j = 0; j < overlay->width; j += 2) {
> x = dest[(i / 2 + y0) * dest_stride + j / 2];
> a = (text_image[4 * (i * overlay->width + j) + 1] +
> text_image[4 * (i * overlay->width + j + 1) + 1] +
> text_image[4 * ((i + 1) * overlay->width + j) + 1] +
> text_image[4 * ((i + 1) * overlay->width + j + 1) + 1] + 2) / 4;
> dest[(i / 2 + y0) * dest_stride + j / 2] = (y * a + x * (255 - a))
> / 255;
> }
> }
> }
>
>
>
> -------------------------------------------------------------------------
> This SF.Net email is sponsored by the Moblin Your Move Developer's challenge
> Build the coolest Linux based applications with Moblin SDK & win great prizes
> Grand prize is a trip for two to an Open Source event anywhere in the world
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> _______________________________________________
> gstreamer-devel mailing list
> [hidden email]
> https://lists.sourceforge.net/lists/listinfo/gstreamer-devel
>
>

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Štěpán Rezek

Re: I420 Color Space

Thank you, it helped me a lot. Now I have to think about vector data
transmission (from client app to gstreamer plugin) and then... My plugin
is finished.
Best regards,
Stepan

Dejan Sakelsak napsal(a):
> check this patches out:
>
> http://bugzilla.gnome.org/show_bug.cgi?id=526670
>
> regards,
> Dejan
>
>

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This SF.Net email is sponsored by the Moblin Your Move Developer's challenge
Build the coolest Linux based applications with Moblin SDK & win great prizes
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