image bitmap data (was: TIFFRepresentation giving me a tiff WITH an alpha)

FROM : Marco Binder
DATE : Tue Nov 19 15:16:23 2002

Since Ben is still struggling with his PDF to grayscale TIFF
conversion, and he is definitly not the only one with trouble like
that, I thought, for the sake of completeness of the archives, I d set
up some quick and dirty sample project, showing how to:

- create an Image from a PDF file
- get the TIFFData from that image and use it for a new image
- create and use the NSBitmapImageRep of the TIFFData and
- use the bitmap data directly to convert it into an 8-bit, 1 sample,
  no alpha grayscale NSBitmapImageRep
- save the resulting grayscale TIFF to disk

Please note that I havent really spent more than an hour on this
project and therefore programming style may have suffered a bit. I
havent optimized it in any way for performance and it is plainly for
illustrating purposes!

You can download it (as a simple .sit) at:
http://www.marco-binder.de/dev/PDF2Grayscale.sit

marco


Am Montag, 18.11.02 um 22:52 Uhr schrieb Ben Mackin:

> On 11/15/02 5:04 AM, "Marco Binder" <<email_removed>> wrote:
>
>> Your problem with "black what should be white" may boil down to the
>> fact, taht what is white is not actually white but R,G,B = 0,0,0 just
>> at alpha 0 which makes it transparent and you got a white background
>> "below" your image. If you now save it without alpha, it s just 0,0,0
>> =
>> black. You ll then have to catch this case (R=0, G=0, B=0, alpha=0)
>> and
>> set the pixel value in your new imageRep to 255 = white.
>
> Would it just work to make every pixel in my imageRep to white first,
> and
> then use the code to convert the image to greyscale. This way the
> background
> would be set to white, and I would have to deal with a check of R=0,
> G=0,
> B=0, and alpha=0?
>
> So if that is the case, and it would work, I was thinking of (looking
> at
> your code) using the following. Unfortunately this doesn't work the
> image
> still is black in all areas that should be white. Maybe my thought
> wasn't
> correct, and I will need to do the RGBA check. Let me know if you spot
> a
> mistake in that code that would not be drawing the white image.
>
> NSBitmapImageRep    *bensRep;
> unsigned char    *data = [imgRep bitmapData];
> unsigned char    *dataPtr;
> int spp = [imgRep samplesPerPixel];
> int bps = ([imgRep bitsPerPixel]/8)/spp;
> int len = [imgRep pixelsHigh]*[imgRep pixelsWide]*spp*bps;
>
> bensRep = [[NSBitmapImageRep alloc]
>        initWithBitmapDataPlanes:NULL
>                      pixelsWide:[imgRep pixelsWide]
>                      pixelsHigh:[imgRep pixelsHigh]
>                    bitsPerSample:8
>                  samplesPerPixel:1
>                        hasAlpha:NO
>                        isPlanar:NO
>                  colorSpaceName:NSCalibratedWhiteColorSpace
>                      bytesPerRow:0
>                    bitsPerPixel:0];
>
> [bensRep setSize:[imgRep size]];
> dataPtr = [bensRep bitmapData];
>
> if (bps==1)
> {
>    int o = 0;
>    int i = 0;
>    for (i=0; i<len; i+=spp)
>    {
>        *(dataPtr+o) = 255;
>        o+=1;
>    }
>
>    o = 0;
>    i = 0;
>    for (i=0; i<len; i+=spp)
>    {
>        int R  = (int)*(data+i);
>        int G  = (int)*(data+i+1);
>        int B  = (int)*(data+i+2);
>        int grayValue = (int)((R+G+B)/3);
>        *(dataPtr+o) = grayValue;
>        o+=1;
>    }
> }
>
> Thanks,
> Ben
>
> http://www.shayufilms.com
>
>
--
|\  /|      E-Mail: <email_removed>  WWW: www.marco-binder.de
| \/ |        Telefon: 07531 / 94 19 94  Fax: 07531 / 94 19 92
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      BINDER _____________________________________________________


--
|\  /|      E-Mail: <email_removed>  WWW: www.marco-binder.de
| \/ |        Telefon: 07531 / 94 19 94  Fax: 07531 / 94 19 92
|    |ARCO        Snail-Mail: Banater Str. 3 - 78467 Konstanz
      BINDER _____________________________________________________
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