{"id":17503,"date":"2009-07-14T10:00:00","date_gmt":"2009-07-14T10:00:00","guid":{"rendered":"https:\/\/blogs.msdn.microsoft.com\/oldnewthing\/2009\/07\/14\/the-fun-and-profit-of-manipulating-the-dib-color-table-can-be-done-without-having-to-modify-it\/"},"modified":"2009-07-14T10:00:00","modified_gmt":"2009-07-14T10:00:00","slug":"the-fun-and-profit-of-manipulating-the-dib-color-table-can-be-done-without-having-to-modify-it","status":"publish","type":"post","link":"https:\/\/devblogs.microsoft.com\/oldnewthing\/20090714-00\/?p=17503","title":{"rendered":"The fun and profit of manipulating the DIB color table can be done without having to modify it"},"content":{"rendered":"

\nIf I were\n\nMichael Kaplan<\/a>,\nI’d have a more clever title like\nI’m not touching you!<\/i>\nor Look but don’t touch<\/i>\nor maybe Looking at a DIB through BITMAPINFO<\/code>-colored\nglasses<\/i>.\n<\/p>\n

\nWe saw\n\nsome time ago<\/a>\nthat you can manipulate the DIB color table to perform wholesale color\nremapping.\nBut in fact you can do this even without modifying the DIB color table,\nwhich is a handy trick if you want to do color remapping but you\ndon’t want to change the bitmap itself.\nFor example,\nthe bitmap is not one that is under your control\n(so you shouldn’t be modifying it),\nor the bitmap might be in use on multiple threads\n(so modifying it will result in race conditions).\n<\/p>\n

\nLet’s demonstrate this technique by converting the “Gone Fishing” bitmap\nto grayscale, but doing so without actually modifying the bitmap.\nAs always, we start with our\n\nscratch program<\/a>\nand make the following changes:\n<\/p>\n

\nHBITMAP g_hbm;<\/font>\n<\/font>\nBOOL\nOnCreate(HWND hwnd, LPCREATESTRUCT lpcs)\n{\n \/\/ change path as appropriate\n g_hbm = (HBITMAP)LoadImage(g_hinst,\n                      TEXT(\"C:\\\\Windows\\\\Gone Fishing.bmp\"),\n                      IMAGE_BITMAP, 0, 0,\n                      LR_CREATEDIBSECTION | LR_LOADFROMFILE);<\/font>\n return TRUE;\n}\nvoid\nOnDestroy(HWND hwnd)\n{\n if (g_hbm) DeleteObject(g_hbm);<\/font>\n PostQuitMessage(0);\n}\nvoid\nPaintContent(HWND hwnd, PAINTSTRUCT *pps)\n{\n if (g_hbm) {\n  BITMAP bm;\n  if (GetObject(g_hbm, sizeof(bm), &bm) == sizeof(bm) &&\n                bm.bmBits != NULL &&\n                bm.bmPlanes<\/a> * bm.bmBitsPixel <= 8) {\n   struct BITMAPINFO256 {\n    BITMAPINFOHEADER bmiHeader;\n    RGBQUAD bmiColors[256];\n   } bmiGray;\n   ZeroMemory<\/a>(&bmiGray, sizeof(bmiGray));\n   HDC hdc = CreateCompatibleDC(NULL);\n   if (hdc) {\n    HBITMAP hbmPrev = SelectBitmap(hdc, g_hbm);\n    UINT cColors = GetDIBColorTable(hdc, 0, 256, bmiGray.bmiColors);\n    for (UINT iColor = 0; iColor < cColors; iColor++) {\n     BYTE b = (BYTE)((30<\/a> * bmiGray.bmiColors[iColor].rgbRed +\n                      59<\/a> * bmiGray.bmiColors[iColor].rgbGreen +\n                      11<\/a> * bmiGray.bmiColors[iColor].rgbBlue) \/ 100);\n     bmiGray.bmiColors[iColor].rgbRed   = b;\n     bmiGray.bmiColors[iColor].rgbGreen = b;\n     bmiGray.bmiColors[iColor].rgbBlue  = b;\n    }\n    bmiGray.bmiHeader.biSize        = sizeof(bmiGray.bmiHeader);\n    bmiGray.bmiHeader.biWidth       = bm.bmWidth;\n    bmiGray.bmiHeader.biHeight      = bm.bmHeight;\n    bmiGray.bmiHeader.biPlanes      = bm.bmPlanes;\n    bmiGray.bmiHeader.biBitCount    = bm.bmBitsPixel;\n    bmiGray.bmiHeader.biCompression = BI_RGB;\n    bmiGray.bmiHeader.biClrUsed     = cColors;\n    SetDIBitsToDevice(pps->hdc, 0, 0,\n                      bmiGray.bmiHeader.biWidth,\n                      bmiGray.bmiHeader.biHeight, 0, 0,\n                      0, bmiGray.bmiHeader.biHeight,\n                      bm.bmBits,\n                     (BITMAPINFO*)&bmiGray, DIB_RGB_COLORS);\n    BitBlt(pps->hdc, bm.bmWidth, 0, bm.bmWidth, bm.bmHeight,\n           hdc, 0, 0, SRCCOPY);\n    SelectBitmap(hdc, hbmPrev);\n    DeleteDC(hdc);\n   }\n  }\n }<\/font>\n}\n<\/pre>\n
\nThings start off innocently enough, loading the bitmap into a\nDIB section for use during painting.\n<\/p>\n
\nWe do our work at paint time.\nFirst, we confirm\nthat we indeed have a DIB section and that it is 8bpp or lower,\nbecause bitmaps at higher than 8bpp do not use color tables.\n<\/p>\n
\nWe then select the bitmap into a DC so we can call\nGetDIBColorTable<\/code> to get its current color table.\n(This is the only step that\nrequires the bitmap to be selected into a device context.)\nWe then edit the color table to convert each color to\nits grayscale equivalent.\n<\/p>\n
\nFinally, we fill in the BITMAPINFO<\/code> structure\nwith the description of the bitmap bits,\nand then we call SetDIBitsToDevice<\/code> to send\nthe pixels to the destination DC.\n<\/p>\n
\nJust for good measure, we also BitBlt<\/code> the\noriginal unmodified bitmap,\nto prove that the original bitmap is intact and unchanged.\n<\/p>\n
\nThis mini-program is really just a stepping stone to other\nthings you can do with this technique of separating the\nmetadata (the BITMAPINFO<\/code>) from the pixels.\nWe’ll continue our investigations tomorrow.\n<\/p>\n
\n(Before you all run out and use this technique everywhere you can imagine,\nwait for the remarks in Friday’s installment.)<\/p>\n","protected":false},"excerpt":{"rendered":"
If I were Michael Kaplan, I’d have a more clever title like I’m not touching you! or Look but don’t touch or maybe Looking at a DIB through BITMAPINFO-colored glasses. We saw some time ago that you can manipulate the DIB color table to perform wholesale color remapping. But in fact you can do this […]<\/p>\n","protected":false},"author":1069,"featured_media":111744,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[1],"tags":[25],"class_list":["post-17503","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-oldnewthing","tag-code"],"acf":[],"blog_post_summary":"
If I were Michael Kaplan, I’d have a more clever title like I’m not touching you! or Look but don’t touch or maybe Looking at a DIB through BITMAPINFO-colored glasses. We saw some time ago that you can manipulate the DIB color table to perform wholesale color remapping. But in fact you can do this […]<\/p>\n","_links":{"self":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/17503","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/users\/1069"}],"replies":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/comments?post=17503"}],"version-history":[{"count":0,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/17503\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/media\/111744"}],"wp:attachment":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/media?parent=17503"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/categories?post=17503"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/tags?post=17503"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}