Re: [Lcms-user] Idiots guide to CMYK->RGB conversions

[<ma...@li...>]

Hi,=20

You almost got it... just replace TYPE_CMYK_16 with TYPE_CMYK_8, and =
SHORT with BYTE,=20
and your program will work.

The buffers are supposed to be arrays of values, since images are stored =
in such way,
the number at end of descriptor (e.g. TYPE_RGB_*) is the number of bits =
per component.=20
TYPE_RGB_8 is 8 bits, so r, g and b are regarded to be BYTEs. =
TYPE_RGB_16 is 16 bits,=20
then r, g, b are WORDs (this is for dealing with 16 bps images, not very =
common). There are=20
many descriptors, lcms can undestand a lot of layouts. As said, this =
works in such way=20
because scanlines of images are stored as arrays of values.

If you want to convert, say, 300 pixels at time, you will need 300 =
pixels x 3 components =3D=20
900 bytes, so you can use output buffer of 900 bytes;

   BYTE OutputBuffer[900];

In CMYK there are 4 components, so 300 x 4 =3D 1200 bytes

    BYTE InputBuffer[1200];

and for converting:

    cmsDoTransform(xform, InputBuffer, OutputBuffer, 300);


Another way to do this could be to use arrays of structs:

struct {
         BYTE r;
         BYTE g;
         BYTE b;

        } MyOutputBuffer[300];
    =20
That is 300, pixels of r, g, b
=20
struct {
         BYTE c;
        BYTE m;
        BYTE y;
        BYTE k;

        } MyInputBuffer[300];

That is, 300 pixels of cmyk

then you could use:=20

cmsDoTransform(xform, MyInputBuffer, MyOutputBuffer, 300)

Note that the number passed are pixels, not bytes.

Hope this helps,
Marti.


  ----- Original Message -----=20
  From: Brian Fallon=20
  To: lcm...@li...=20
  Sent: Saturday, April 28, 2001 6:57 PM
  Subject: [Lcms-user] Idiots guide to CMYK->RGB conversions


  Hi,

  I've looked at every message on this list and I can't figure out how =
to convert CMYK values into RGB values using the API

  I understand fully the concepts beign used here but I'm a total =
beginner when it comes to the C language.

  Please, please, could you send me some code on how to do this... If =
not please explain my question below.

  I've looked at the 'simple.c' file included with the source and I cant =
figure how to use it? What type are inputBuffer & outputBuffer. Do I =
pass an array of values into the function cmsDoTransform()?

  here is what I have being messing around with so far (see below), If =
anyone could make this work I would be able to adapt it into a simple =
program and that's all I need. Thanks a million....

  Brian Fallon


   SHORT inputBuffer[] =3D {0x00,0x00,0x00,0x00};
   SHORT outputBuffer[3];

      cmsHPROFILE hInProfile, hOutProfile;
      cmsHTRANSFORM hTransform;

      hInProfile  =3D =
cmsOpenProfileFromFile("D:/Downloads/Development/lcms/lcms107b/profiles/t=
r01_d50.icm", "r");
      hOutProfile =3D =
cmsOpenProfileFromFile("D:/Downloads/Development/lcms/Lcms107b/profiles/s=
RGB Color Space Profile.ICM", "r");=20
   hTransform =3D cmsCreateTransform(hInProfile, TYPE_CMYK_16, =
hOutProfile, TYPE_RGB_8, INTENT_PERCEPTUAL, 0);


   cmsDoTransform(hTransform, inputBuffer, outputBuffer, 1);


      cmsDeleteTransform(hTransform);
      cmsCloseProfile(hInProfile);
      cmsCloseProfile(hOutProfile);

   printf("Input values: cmyk( %d, %d, %d, %d )\n", inputBuffer[0], =
inputBuffer[1], inputBuffer[2], inputBuffer[3]);
   printf("Input values: rgb( %d, %d, %d)\n", outputBuffer[0], =
outputBuffer[1], outputBuffer[2]);
   return 0;=20
  }