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silvia_steven_2000

TGA texture : again

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Hi Guys please bare with me, I am opening a new thread for the same issue that I was asking about on the directx forum: by the way is there a way to upload images to the forum so that one can demonstrate the question ? I am trying to load a TGA file and use it to texture map a cube. No compression nor encoding is used. the TGA color format is 24 bit BGR. what I do is fairly simple: I just load the image data block into memory and convert it to RGB. then I created another memory buffer that has the format of XRGB and copied the image data into the new buffer. the x is filled with 1 and the rgb are filled with the TGA rgb values. I then created an empty DX9 texture of the format xrgb. I used memcpy to copy the image buffer to the texture surface. I had two problems that I can not explain. 1) the texture is dimmed and looks darker than the original picture but it is not distorted. I do not think it is something to do with lighting, blending or materials. I think it is something to do with loading the image in the first place. I am saying that because I used the D3DX function to create the texture using the same render states and it looks bright as expected. somebody told me about gamma correction. I never used but it might be the reason behind that. 2) another weird problem is that I was able to load a picture once. it was not distorted but was dimmed as mentioned earlier. what was surprising is that I loaded another picture using the same code. the loaded picture was dimmed as before but the strange thing is that it was flipped 180 degrees along the vertical direction. I have two questions: I though that just coping the image to the texture row by row is wrong and DX9 stores the image column by column. but still I had the first picture not flipped. what is going on ? is there some field in the tga that says how the pixels are ordered. ?

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1) To apply gamma to an image, raise each color component to the power of 1/gamma. I'd use a 256-entry table to do this.. or else you'd need a floating-point pow() per component per pixel. If you want more information on gamma, see the colorspace faq

2) The TGA spec is full of all sorts of useful information:
"Image Specification - Field 5 (10 bytes):
Bits 5 & 4: These bits are used to indicate the order in which pixel data is transferred from the file to the screen. Bit 4 is for left-to-right ordering and bit 5 is for top-to-bottom ordering as shown below."

3) I wouldn't use memcpy to copy your whole image into the texture. This blindly assumes width equals pitch, which is up to the driver, and not guaranteed. Instead, memcpy the bits a scanline at a time.

xyzzy

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