C code production YUV420 planar format file

YUV420 knowledge

For all YUV420 Images , Their Y The values are arranged exactly the same , Because only Y The image of is a grayscale image .

YUV420 According to the storage form , It is divided into YUV420sp（semi-Planar Half plane ） And YUV420p（planar Plane ）, Their data format is UV The arrangement is different .420p It is to put U perhaps V After storage , Re storage V perhaps U, in other words UV They are continuous , and 420sp yes UV Alternate storage .

I420（YU12） and YV12 Belong to YUV420p Format , take Y、U、V Pack the components separately , Store... In sequence .NV12 And NV21 similar ,U and V staggered , Belong to YUV420sp.

YUV 4:2:0 sampling , Every four Y Share a group UV component . therefore , Work out a YUV420 The size of storage in memory , It's below. Y,U,V The sum of the sizes of the components , namely ：Y+U+V => width * height * 3/2

Y = width * hight
U = Y / 4
V = Y / 4

Icon ：1 A pixel YUV Storage , Each letter represents a ,

I420: YYYYYYYY UUVV  =>  YUV420P
YV12: YYYYYYYY VVUU  =>  YUV420P
NV12: YYYYYYYY UVUV  =>  UV420SP
NV21: YYYYYYYY VUVU  =>  YUV420SP

In the name ,“YV” Represents the plane order ：Y, then V（ then U）.12 Refers to pixel depth ： about YV12, Each pixel 12 position .NV12 Medium 12 It also means per pixel 12 position .

Grey white YUV

The following code produces a 1080x720 Of YUV file , The format is YUV420 planar, about planar Of YUV Format , First, store all pixels in a row Y, And then it stores all the pixels U, And then all the pixels V.

therefore ,data Its size is width * height * 3 / 2, First write width * height Size data , Color bit 0xb4, To write width * height / 2 The size of as uv The data of , Here's the choice UV The color is the same , So I wrote together . The document written in this way has been used ubuntu Upper YUVView Tool view is grayish white .

int width = 1080;
int height = 720;
int size = width * height * 3 / 2;
uint8_t *data = (uint8_t *)malloc(size);

memset(data, 0xb4, size); 
fwrite(data, width * height, 1, fp); // write y data

memset(data + width*height, 0x80, size);
fwrite(data, width*height/2, 1, fp); //write uv data
fclose(fp);

Cyan YUV

The size of the cyan file definition is 8x8 The file of , Because discovery passed YUVView Tools , Zoom in 8x8 Of YUV After the image , You can see clearly YUV The distribution of components in the picture .

Apply first in the following code data Memory , Then set different values , Finally, write by size .

int width = 8;
int height = 8;
int size = width * height * 3 / 2;
uint8_t *data = (uint8_t *)malloc(size);


// set Y to 131
memset(data, 0x83/* 131 */, width*height);
// set U to 156
memset(data + width*height, 0x9c/* 156 */, width*height/4);
// set V to 44
memset(data + width*height + width*height/4, 0x2c/* 44 */, width*height/4);

FILE* fp = nullptr;
fp = fopen("/sdcard/h264.yuv", "wb");
// write Y
fwrite(data, width * height, 1, fp);
// write UV
fwrite(data+ width*height, width*height/2, 1, fp);
fclose(fp);

adopt ubuntu On YUView Tools , Zoom in to 64 times , You can see that YUV Distribution of ,YUV420 One of the four points UV value ：

Replace the code with an array

width = 8;
height = 8;
int size = width * height * 3 / 2;
uint8_t *data = (uint8_t *)malloc(size);
memset(data, 0, size);

FILE* fp = nullptr;
fp = fopen("/sdcard/h264.yuv", "wb");

// set Y to 131
for(int i = 0; i < height; i++) {
    
    for(int j = 0; j < width; j++) {
    
        data[i*width + j] = 131;
    }
}

// set U to 156
int offset = width * height;
for(int i = 0; i < height/4; i++) {
    
    for(int j = 0; j < width; j++) {
    
        data[offset + i*width + j] = 156;
    }
}

// set V to 45
offset = width*height + width*height/4;
for(int i = 0; i < height/4; i++) {
    
    for(int j = 0; j < width; j++) {
    
        data[offset + i*width + j] = 45;
    }
}

fwrite(data, width * height, 1, fp);
//write UV
fwrite(data+ width*height, width*height/2, 1, fp);

fclose(fp);        

YUView see , And the one in front V Values are not the same ：

The color table reference in the previous code

	Nominal range	white	yellow	Cyan	green	Red	Blue	black
Y	16~235	180	162	131	112	65	35	16
Cb	16~240	128	44	156	72	100	212	128
Cr	16~240	128	142	44	58	212	114	128

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