glColorTableExt for gray scale palette

OpenGL OpenGL: Advanced Coding
1

Is it possible to define a gray scale plette with glColorTableExt ? How ? What are the parameters ?

I succeeded to define 8 bits palette for green levels. But not gray.

What will be the parameters for glTexImage2D ?

Thanks in advance.

2

basically grayscale pictures doesn’t need palettes bcoz colors are stored as intensity (8bits) so if u need to translate your bitmap as indexes->palette just fill each r,g,b with the same value.
Now if you’ve planned to use grayscale pics i strongly recommend to also use the shared palette extension which will save a little bit of time when binding textures.

switch(pPicInfos->type){
	case BITMAP_4B:
		pBitmap->infos.format = VR_RGB4;
		pBitmap->infos.bpp = 8;
	
		if(glColorTableEXT == NULL)
			goto convto15;

		picConvert(pPicInfos,CONVERT_TO_8);

		glColorTableEXT(GL_TEXTURE_2D,GL_RGB,16,GL_RGB,GL_UNSIGNED_BYTE,pPicInfos->pPalette);
	
		glTexImage2D(GL_TEXTURE_2D,0,GL_COLOR_INDEX4_EXT,w,h,0,GL_COLOR_INDEX,GL_UNSIGNED_BYTE,pPicInfos->pData);
		break;
	case BITMAP_8B:
		pBitmap->infos.format = VR_RGB8;
		pBitmap->infos.bpp = 8;
		
		if(glColorTableEXT == NULL)
			goto convto15;

		glDisable(GL_SHARED_TEXTURE_PALETTE_EXT);
		glColorTableEXT(GL_TEXTURE_2D,GL_RGB,256,GL_RGB,GL_UNSIGNED_BYTE,pPicInfos->pPalette);
		glTexImage2D(GL_TEXTURE_2D,0,GL_COLOR_INDEX8_EXT,w,h,0,GL_COLOR_INDEX,GL_UNSIGNED_BYTE,pPicInfos->pData);
		break;
	case BITMAP_GRAYSCALE:
		pBitmap->infos.format = VR_GRAYSCALE;
		pBitmap->infos.bpp = 8;
	
		if(glColorTableEXT == NULL)
			goto convto15;

		glEnable(GL_SHARED_TEXTURE_PALETTE_EXT);
		if (!sharedPaletteLoaded){
			glColorTableEXT(GL_SHARED_TEXTURE_PALETTE_EXT,GL_RGB,256,GL_RGB,GL_UNSIGNED_BYTE,pPicInfos->pPalette);
			sharedPaletteLoaded = VR_TRUE;

		}
		glTexImage2D(GL_TEXTURE_2D,0,GL_COLOR_INDEX8_EXT,w,h,0,GL_COLOR_INDEX,GL_UNSIGNED_BYTE,pPicInfos->pData);
		break;

hth

3

If all you’re doing is grayscale, don’t use palette at all. Instead, use GL_ALPHA or GL_LUMINANCE texture formats (and, probably, external formats).