How to take a 8bit grey scale image screenshot

[westpointer]

The default writeContentsToFile method only take a RGB image screenshot,
How to take a 8bit grey scale image screenshot?

[syedhs]

The code for writeContentsToFile is quite simple, found at OgreRenderTarget.cpp :-

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		PixelFormat pf = suggestPixelFormat();

		uchar *data = OGRE_ALLOC_T(uchar, mWidth * mHeight * PixelUtil::getNumElemBytes(pf), MEMCATEGORY_RENDERSYS);
		PixelBox pb(mWidth, mHeight, 1, pf, data);

		copyContentsToMemory(pb);

		Image().loadDynamicImage(data, mWidth, mHeight, 1, pf, false, 1, 0).save(filename);

		OGRE_FREE(data, MEMCATEGORY_RENDERSYS);

You can probably try it yourself by copy-pasting the code above somewhere, changing the first line into

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PixelFormat pf = PF_L8;

I don't really know whether this will work, but you can give it a test

[westpointer]

Yes, It works. But when I try to save a RTT texture to file, the result looks confusing:

Here is the code:

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      PixelFormat pf = PF_L8;

      Ogre::TexturePtr texture = Ogre::TextureManager::getSingleton().createManual("RttTex",
		ResourceGroupManager::DEFAULT_RESOURCE_GROUP_NAME, TEX_TYPE_2D, width, height, 0, pf, TU_RENDERTARGET);

      Ogre::RenderTexture *renderTexture = texture->getBuffer(0,0)->getRenderTarget();
      renderTexture->addViewport(mCamera);
      renderTexture->getViewport(0)->setClearEveryFrame(true);
      renderTexture->getViewport(0)->setBackgroundColour(ColourValue::Black);
      renderTexture->getViewport(0)->setOverlaysEnabled(false);
      renderTexture->setAutoUpdated(true);	     

      uchar *data = OGRE_ALLOC_T(uchar, mWidth * mHeight * PixelUtil::getNumElemBytes(pf), MEMCATEGORY_RENDERSYS);
      PixelBox pb(mWidth, mHeight, 1, pf, data);

      renderTexture->copyContentsToMemory(pb,Ogre::RenderTarget::FB_AUTO);

      Image().loadDynamicImage(data, mWidth, mHeight, 1, pf, false, 1, 0).save(filename);

      OGRE_FREE(data, MEMCATEGORY_RENDERSYS);

[westpointer]

I find that the problem comes from this line:

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renderTexture->setAutoUpdated(true);    

after change it to:

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renderTexture->update(); 

the result is just OK.
But in http://www.ogre3d.org/wiki/index.php/In ... Tutorial_7, it says:

You can do this either manually via the update() function or request the application to automatically update the RenderTexture by once calling the setAutoUpdate() function.

Quite confusing

Edit: Damn it, it is all my fault, I shouldn't call setAutoUpdate() every time I take a screenshot.