How to get rendered pixel value of IImage?

[verilogdc]

I use createScreenShot to get a IImage* screenshot and then use writeImageToFile to save it as "screenshot.png".
However, I found that screenshot->getPixel will not get the same pixel value as "screenshot.png", it will be darker than "screenshot.png". I guess it is because screenshot->getPixel gets the pixel value before rendering. Is it true? How to get rendered pixel value of IImage?

Code: Select all

virtual IImage * createScreenShot (video::ECOLOR_FORMAT format=video::ECF_UNKNOWN, video::E_RENDER_TARGET target=video::ERT_FRAME_BUFFER)=0
virtual bool writeImageToFile (IImage *image, const io::path &filename, u32 param=0)=0
virtual SColor getPixel (u32 x, u32 y) const =0

[chronologicaldot]

I can't really tell what you're doing without some code. However, I will say this: You have to render the scene to the render target (which ends by calling IVideoDriver::endScene()), which I believe must precede calling createScreenShot(). I haven't used createScreenShot(), but I do read the API.

Instead of using createScreenShot(), you can create an IRenderTarget, which is created via addRenderTargetTexture():
http://irrlicht.sourceforge.net/docu/cl ... 054b0b8797
You can set it with setRenderTarget()
http://irrlicht.sourceforge.net/docu/cl ... 6bcaaeba9c
You can even just set a texture as the render target with setRenderTarget(), but (never tried this) I believe this means it isn't also rendered to the screen.
Note, you will have to convert the texture (ITexture) to an image (IImage) via createImage():
http://irrlicht.sourceforge.net/docu/cl ... 59c3dc8fae
And from there, you can access the pixels with getPixel().

[mongoose7]

Why not just create a screenshot from the frame buffer? I have created screenshots and written them to files and they have been pixel perfect. However, I used the BMP format. The PNG format is quite complex, I think, so perhaps there is some compression there? Anyway, you certainly must wait until the scene is rendered before taking the screenshot, perhaps after the endScene() call.

[CuteAlien]

Hm, can't really think of a reason why png whould get darker on saving. Can you reproduce this in a short example which we can compile and test?

[hendu]

Could be the PNG's gamma correction? Use a program that ignores it, or remove the gamma chunk with PNG tools to test.

That is, the pixel value is intact, but your viewer might convert it upon opening.

[chronologicaldot]

I wonder... It may have to do with the color format of the screenshot itself, which is then converted to png.
@verilogdc - What is your video::ECOLOR_FORMAT set to?