GIFLIB
上一篇 【手动生成一张GIF图片】, 自己生成了一张 GIF 动态图 rainbow.gif。
rainbow.gif
下面，使用 GIFLIB 分离出 GIF 每一帧的 RGB ，然后将分离出的 RGB 再合成 GIF。
GIF to RGB
GIFLIB 项目里的 gif2rgb.c 已经实现了解码 GIF -> RGB。不过 gif2rgb.c 只保存了最后一帧图片的 RGB，这里需要改造。
gif2rgb.c
gif2rgb.c 在 GIF2RGB 方法最后才调用 DumpScreen2RGB 保存 RGB。
......
static void DumpScreen2RGB(char *FileName,
ColorMapObject *ColorMap,
GifRowType *ScreenBuffer,
int ScreenWidth, int ScreenHeight)
{
......
}
static void GIF2RGB(int NumFiles, char *FileName,
bool OneFileFlag,
char *OutFileName)
{
......
/* Scan the content of the GIF file and load the image(s) in: */
do {
......
} while (RecordType != TERMINATE_RECORD_TYPE);
/* Lets dump it - set the global variables required and do it: */
ColorMap = (GifFile->Image.ColorMap
? GifFile->Image.ColorMap
: GifFile->SColorMap);
if (ColorMap == NULL) {
fprintf(stderr, "Gif Image does not have a colormap\n");
exit(EXIT_FAILURE);
}
/* check that the background color isn't garbage (SF bug #87) */
if (GifFile->SBackGroundColor < 0 || GifFile->SBackGroundColor >= ColorMap->ColorCount) {
fprintf(stderr, "Background color out of range for colormap\n");
exit(EXIT_FAILURE);
}
DumpScreen2RGB(OutFileName, OneFileFlag,
ColorMap,
ScreenBuffer,
GifFile->SWidth, GifFile->SHeight);
(void)free(ScreenBuffer);
if (DGifCloseFile(GifFile, &Error) == GIF_ERROR) {
PrintGifError(Error);
exit(EXIT_FAILURE);
}
}
gif-to-rgb-library.c
需要把调用 DumpScreen2RGB 的位置移到循环体内 case IMAGE_DESC_RECORD_TYPE: 位置。
......
static void DumpScreen2RGB(char *FileName,
ColorMapObject *ColorMap,
GifRowType *ScreenBuffer,
int ScreenWidth, int ScreenHeight)
{
......
}
static void GIF2RGB( char *FileName, char *OutFileNamePattern)
{
......
do {
......
switch (RecordType) {
case IMAGE_DESC_RECORD_TYPE:
......
ColorMap = (GifFile->Image.ColorMap
? GifFile->Image.ColorMap
: GifFile->SColorMap);
if (ColorMap == NULL) {
fprintf(stderr, "Gif Image does not have a colormap\n");
exit(EXIT_FAILURE);
}
/* check that the background color isn't garbage (SF bug #87) */
if (GifFile->SBackGroundColor < 0 || GifFile->SBackGroundColor >= ColorMap->ColorCount) {
fprintf(stderr, "Background color out of range for colormap\n");
exit(EXIT_FAILURE);
}
char *name = malloc(255*sizeof(char));
sprintf(name, OutFileNamePattern, screenIndex++);
printf("Final File Name: %s\n", name);
DumpScreen2RGB(name,
ColorMap,
ScreenBuffer,
GifFile->SWidth, GifFile->SHeight);
break;
case EXTENSION_RECORD_TYPE:
......
}
} while (RecordType != TERMINATE_RECORD_TYPE);
......
}
int main(int argc, char **argv) {
GIF2RGB( "/Users/staff/Desktop/rainbow.gif", "/Users/staff/Desktop/rainbow-%d.rgb");
return 0;
}
查看 GIF -> RGB 结果
根据 【手动生成一张GIF图片】 生成的 GIF rainbow.gif 含有 7 个图像，所以会得到 7 个 .RGB 文件。
ffplay 查看 RGB 文件：
ffplay -f rawvideo -pixel_format rgb24 -s 700x700 rainbow-0.rgb
ffplay -f rawvideo -pixel_format rgb24 -s 700x700 rainbow-1.rgb
ffplay -f rawvideo -pixel_format rgb24 -s 700x700 rainbow-2.rgb
ffplay -f rawvideo -pixel_format rgb24 -s 700x700 rainbow-3.rgb
ffplay -f rawvideo -pixel_format rgb24 -s 700x700 rainbow-4.rgb
ffplay -f rawvideo -pixel_format rgb24 -s 700x700 rainbow-5.rgb
ffplay -f rawvideo -pixel_format rgb24 -s 700x700 rainbow-6.rgb
decode-gif-to-rgb.jpg
RGB to GIF
上面，从 rainbow.gif 中提取出了 7 个 RGB 文件。
下面，读取这 7 个 RGB 文件，使用 GIFLIB 编码成 GIF 动态图。
// LoadRGB 是 gif2rgb.c 文件中的方法
static void LoadRGB(char *FileName,
GifByteType **RedBuffer,
GifByteType **GreenBuffer,
GifByteType **BlueBuffer,
int Width, int Height)
{
......
}
// gif2rgb.c 文件中 RGB2GIF 只实现了 RGB to GIF 静态图功能
// 这里做了修改，可以生成动态 GIF
static void RGB2GIF(char **RGBFileNames, int NumOfRGBFile, char *GIFFileName,
int ExpNumOfColors, int Width, int Height)
{
int ColorMapSize;
GifByteType *RedBuffer = NULL, *GreenBuffer = NULL, *BlueBuffer = NULL, *OutputBuffer = NULL;
ColorMapObject *OutputColorMap = NULL;
// 打开输出的 GIF 文件
int Error;
GifFileType *GifFile;
if ((GifFile = EGifOpenFileName(GIFFileName, false, &Error)) == NULL) {
PrintGifError(Error);
exit(EXIT_FAILURE);
}
GifFile->SWidth = Width;
GifFile->SHeight = Height;
GifFile->SColorResolution = 1;
GifFile->SBackGroundColor = 0;
GifFile->SColorMap = NULL;
for(int i = 0; i < NumOfRGBFile; i++) {
ColorMapSize = 1 << ExpNumOfColors;
printf("读取 RGB 文件：%d\n", i);
LoadRGB(RGBFileNames[i], &RedBuffer, &GreenBuffer, &BlueBuffer, Width, Height);
if ((OutputColorMap = GifMakeMapObject(ColorMapSize, NULL)) == NULL ||
(OutputBuffer = (GifByteType *) malloc(Width * Height *
sizeof(GifByteType))) == NULL)
GIF_EXIT("Failed to allocate memory required, aborted.");
if (GifQuantizeBuffer(Width, Height, &ColorMapSize,
RedBuffer, GreenBuffer, BlueBuffer,
OutputBuffer, OutputColorMap->Colors) == GIF_ERROR)
exit(EXIT_FAILURE);
free((char *) RedBuffer);
free((char *) GreenBuffer);
free((char *) BlueBuffer);
printf("MakeSavedImage：%d\n", i);
SavedImage *image = GifMakeSavedImage(GifFile, NULL);
GifImageDesc *imageDesc = (GifImageDesc *) malloc(sizeof(GifImageDesc));
imageDesc->Left = 0;
imageDesc->Top = 0;
imageDesc->Width = Width;
imageDesc->Height = Height;
imageDesc->Interlace = false;
imageDesc->ColorMap = OutputColorMap;
image->ImageDesc = *imageDesc;
image->RasterBits = OutputBuffer;
GraphicsControlBlock *GCB = (GraphicsControlBlock *) malloc(sizeof(GraphicsControlBlock));
GCB->DisposalMode = DISPOSAL_UNSPECIFIED;
GCB->DelayTime = 50;
GCB->UserInputFlag = false;
GCB->TransparentColor = NO_TRANSPARENT_COLOR;
printf("GCBToSaved：%d\n", i);
EGifGCBToSavedExtension(GCB, GifFile, i);
}
printf("输出文件。");
// 输出文件
EGifSpew(GifFile);
}
int main(int argc, char **argv) {
char *rgbFiles[] = {
"/Users/staff/Desktop/rainbow-0.rgb",
"/Users/staff/Desktop/rainbow-1.rgb",
"/Users/staff/Desktop/rainbow-2.rgb",
"/Users/staff/Desktop/rainbow-3.rgb",
"/Users/staff/Desktop/rainbow-4.rgb",
"/Users/staff/Desktop/rainbow-5.rgb",
"/Users/staff/Desktop/rainbow-6.rgb",
};
RGB2GIF(rgbFiles, 7, "/Users/staff/Desktop/rainbow0.gif", 3, 700, 700);
return 0;
}
查看 RGB -> GIF 结果
成功实现了 GIF -> RGB(s) -> GIF。
gif-rgb-gif.jpg
encode-rgb-to-gif.jpg
参考资料：
How do I get the RGB colour data from a GIFLIB SavedImage structure
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