Scaling MultipassBitmap with Alpha [SOLVED]

Helper

On 16/07/2015 at 12:17, xxxxxxxx wrote:

User Information:
Cinema 4D Version:
Platform:
Language(s) :

---------
Having an issue where a multiples bitmap will not keep its alpha when scaled.

bitmap is a multipass bitmap with alpha. That has been verified in code and with a render to disk.

The scaling is anamorphic.

MultipassBitmap *scaled_bitmap = MultipassBitmap::Alloc(20,60,COLORMODE_RGB);
scaled_bitmap->AddChannel(true,true);
bitmap->ScaleIt(scaled_bitmap,256,true,true);

What is saved is a tif without alpha. If I simply change to saving bitmap I get the correct render with alpha.

What can I do to keep the alpha and have it scale?

thank you,
Ama

Helper

On 16/07/2015 at 13:43, xxxxxxxx wrote:

ScaleIt() is only defined in BaseBitmap which would make me think that it can't handle a MultipassBitmap properly or without some consideration. Or it is something about using AddChannel() - again only defined in BaseBitmap. Why do you not allocate using COLORMODE_ARGB or use the MultipassBitmap::AddAlpha()?

Hopefully you do not need to resort to GetLayers() and using ScaleIt() on each BaseBitmap in the returned array.

Helper

On 16/07/2015 at 13:46, xxxxxxxx wrote:

I was rendering a document and using the suggested functions in the documentation. MultipassBitmap seemed to be the only way it worked.

thank you,
Ama

Originally posted by xxxxxxxx

ScaleIt() is only defined in BaseBitmap which would make me think that it can't handle a MultipassBitmap properly or without some consideration. Or it is something about using AddChannel() - again only defined in BaseBitmap. Why do you not allocate using COLORMODE_ARGB or use the MultipassBitmap::AddAlpha()?

Hopefully you do not need to resort to GetLayers() and using ScaleIt() on each BaseBitmap in the returned array.

Helper

On 17/07/2015 at 06:47, xxxxxxxx wrote:

Hello,

MultipassBitmap actually overrides AddChannel() internally and does not create a "channel" but a alpha layer. But ScaleIt() is indeed a method that can only handle BaseBitmaps and their internal channels, so it cannot scale layers.

So you either stick to BaseBitmaps or you have to handle the layers/channels manually.

Best wishes,
Sebastian

Helper

On 17/07/2015 at 07:01, xxxxxxxx wrote:

What is the appropriate way to create a basebitmap from the multiples bitmap with alpha?

Ama

Originally posted by xxxxxxxx

Hello,

MultipassBitmap actually overrides AddChannel() internally and does not create a "channel" but a alpha layer. But ScaleIt() is indeed a method that can only handle BaseBitmaps and their internal channels, so it cannot scale layers.

So you either stick to BaseBitmaps or you have to handle the layers/channels manually.

Best wishes,
Sebastian

Helper

On 17/07/2015 at 07:30, xxxxxxxx wrote:

Is there a way to create a basebitmap with alpha to work with renderdocument?

Ama

Helper

On 20/07/2015 at 04:56, xxxxxxxx wrote:

Hello,

as discussed on different threads, one must use a MultipassBitmap to render alpha layers with RenderDocument.

It seems there is no build-in functionality to handle your specific use case. So you might have to copy an alpha layer yourself into a BaseBitmap. This could look like this:

  
const Int32 alphaLayerCount = mpBitmap->GetAlphaLayerCount();  
  
for(Int32 i = 0; i < alphaLayerCount; ++i)  
{  
  
 MultipassBitmap* alphaChannel = mpBitmap->GetAlphaLayerNum(i);  
  
  const Int32 h = alphaChannel->GetBh();  
 const Int32 w = alphaChannel->GetBw();  
  
 // create basebitmap  
 BaseBitmap* temp = BaseBitmap::Alloc();  
 temp->Init(w, h, COLORMODE_RGBf);  
  
  
 // copy  
  
 UChar* buf= NewMem(UChar, w);  
 Float32* rgbBuf = NewMem(Float32, w * 3);  
  
 for(Int32 line = 0; line < h; ++line)  
 {  
     // get pixels  
     alphaChannel->GetPixelCnt(0, line, w, buf, 1, COLORMODE_GRAY, PIXELCNT_0);  
  
     for(Int32  x = 0; x < w; ++x)  
     {  
         // read  
         UChar grey = buf[x];  
  
         Float greyF =  Float32(grey) / 256.0;  
  
         // write  
         rgbBuf[3*x] = greyF;  
         rgbBuf[3*x+1] = greyF;  
         rgbBuf[3*x+2] = greyF;  
     }  
  
     // set pixels  
     temp->SetPixelCnt(0,line,w,(UChar* )rgbBuf,3 * sizeof(Float32),COLORMODE_RGBf,PIXELCNT_0);  
 }  
 // free memory  
 DeleteMem(buf);  
 DeleteMem(rgbBuf);  
  
 // create small bitmap and scale  
 BaseBitmap* smallBitmap = BaseBitmap::Alloc();  
 smallBitmap->Init(400, 300, COLORMODE_RGBf);  
 temp->ScaleIt(smallBitmap, 256, true, false);  
       
  // show results  
  ShowBitmap(temp);  
  ShowBitmap(smallBitmap);  
  
  // free memory  
  BaseBitmap::Free(smallBitmap);  
  BaseBitmap::Free(temp);  
}

best wishes,
Sebastian

Helper

On 20/07/2015 at 05:01, xxxxxxxx wrote:

Thank you!

Ama