Hi Michael,
I think you are assuming T_BYTES() returns the number of bytes per
pixel when it really returns bytes per channel. Also, you are mixing
cmsColorSpaceSignature with formatters.
Just use this:
nOutputFormatter = BYTES_SH(1) | CHANNELS_SH(nNumOutputChannels);
This is enough. You can do an additional colorspace check by using
nOutputFormatter |=
COLORSPACE_SH(_cmsLCMScolorSpace((cmsColorSpaceSignature(hProfile)));
Plese note the "_" at the begin of _cmsLCMScolorSpace, and that means
you should not need this function in normal operation. If fact, the
colorspace (color model to be more precise) of the image is not given
by the profile but by the image itself. As an example, I can embed a
RGB profile into a CMYK image. Using the algorithm above would not
work. I would check both color models to validate the profile before
proceeding to do the color transformation.
Regards
Marti
Quoting Michael Zauner <psychotro...@gmx.ch>:
> Hi,
>
> I do love little CMS very much - nice, small and quick.
> But I do have an issue with a bit of code and I cannot see what I am
> doing wrong.
> Maybe one of you guys could help me and tell if I do anything obvious
> stupid?
>
> The basic idea is that I do have an image with an embedded profile and
> an external profile file.
> The external profile can differ and may have e.g. 6 channels.
> I want to transform the image with the external profile and read the
> pixel values of the output channels.
>
> Here is an example code (leaving out only the input image specific
> stuff), which is really a modified version of the basic example seen in
> the tutorial:
>
> //START
>
> cmsHPROFILE hInProfile, hOutProfile;
> cmsHTRANSFORM hTransform;
>
> //Width and height and pixel type are from the input image
> int nInputPixelType = TYPE_BGRA_16;
> int nWidth = xxx;
> int nHeight = xxx;
>
> //Loading the profiles
> hInProfile = cmsOpenProfileFromMem(memoryPointer,size);
> hOutProfile = cmsOpenProfileFromFile(szProfileFile, "r");
>
> //Extracting information of the output profile
> cmsColorSpaceSignature outputColorSpace = cmsGetColorSpace(hOutProfile);
> int nNumOutputChannels = cmsChannelsOf(outputColorSpace); //This is 6 in
> my example
> //This formatter is used in the transformation
> int nOutputFormatter = _cmsLCMScolorSpace(outputColorSpace);
> int nNumBytes = T_BYTES(nOutputFormatter); //This is 4 in my example
>
> //I change now the formatter to have 1 byte instead as I want to use
> that instead of 4 byte precision
> if(nNumBytes != 1)
> {
> //Clear the first 3 bits
> nOutputFormatter &= ~7;
> //Set it to 1 Bytes
> nOutputFormatter |= 1;
> //Retrieve the value again (making sure it is one byte)
> nNumBytes = T_BYTES(nOutputFormatter);
> }
>
> //Create the transformation
> hTransform = cmsCreateTransform(hInProfile, nInputPixelType,
> hOutProfile, nOutputFormatter,
> INTENT_RELATIVE_COLORIMETRIC, 0);
>
> //Closing the profile
> cmsCloseProfile(hInProfile);
> cmsCloseProfile(hOutProfile);
>
> //Create a buffer to hold the transformed data
> int nNewSizeInBytes = nNumOutputChannels * nHeight * nWidth * nNumBytes;
> char* szData = new char[nNewSizeInBytes];
> memset(szData,0,nNewSizeInBytes);
>
> //Transform the data
> int nRowLengthInBytes = nNumOutputChannels*nNumBytes*nWidth;
> for(int i = 0; i < nHeight; ++i)
> {
> char* pixelBuffer = READ_BUFFER_FROM_IMAGE_FOR_ROW(i);
> cmsDoTransform(hTransform, pixelBuffer,szData + i
> *nRowLengthInBytes, nWidth);
> }
>
> //END
>
> The issue is that the transformation does work - I do get the data for
> each channel. But the transformed image data is only 1/3 wide (the
> height does match) - the other 2/3 of the image are untouched (e.g. when
> I initialize szData with white instead of black, it remains white).
> I must be doing something really stupid - but I cannot see what is wrong?
>
> Any help or pointers are highly appriciated.
> It would help me to know if the litte CMS code is ok but I have an issue
> either in the input buffer or the output buffer?
>
> Thank you very much in advance
>
> Michael
>
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