If the image comming from a camera device create raw data image:

1- bool RawImage::create( int width, int height, int channels )
2- write your buffer RawImage::QByteArray data....
3- at end QImage convertToQImage(bool cmyk = false , bool raw = false);

( idea from www.scribus.net code )

Qt Code: 
  1. /////  header
  2. #ifndef RAWIMAGE_H
  3. #define RAWIMAGE_H
  4.  
  5. #include <QtGui>
  6.  
  7. class RawImage : public QByteArray
  8. {
  9. public:
  10.     RawImage();
  11.     RawImage( int width, int height, int channels);
  12.     ~RawImage();
  13.     bool create( int width, int height, int channels);
  14.     int width()  const {
  15.         return m_width;
  16.     };
  17.     int height()  const {
  18.         return m_height;
  19.     };
  20.     int channels()  const {
  21.         return m_channels;
  22.     };
  23.     uchar *bits() {
  24.         return (uchar*)data();
  25.     };
  26.     uchar *scanLine(int row);
  27.     void setAlpha(int x, int y, int alpha);
  28.     QImage convertToQImage(bool cmyk = false , bool raw = false);
  29. private:
  30.     int m_width;
  31.     int m_height;
  32.     int m_channels;
  33. };
  34.  
  35.  
  36. #endif
  37. ///// source
  38.  
  39. #include "rawimage.h"
  40.  
  41.  
  42. RawImage::RawImage()
  43. {
  44.     m_width = 0;
  45.     m_height = 0;
  46.     m_channels = 0;
  47.     resize(0);
  48. }
  49.  
  50. RawImage::RawImage( int width, int height, int channels )
  51. {
  52.     create(width, height, channels);
  53. }
  54.  
  55. RawImage::~RawImage()
  56. {
  57.     resize(0);
  58. }
  59.  
  60. bool RawImage::create( int width, int height, int channels )
  61. {
  62.     m_width = width;
  63.     m_height = height;
  64.     m_channels = channels;
  65.     int finalSize=width * height * channels;
  66.     resize(finalSize);
  67.     return (size()==finalSize);
  68. }
  69.  
  70. uchar *RawImage::scanLine(int row)
  71. {
  72.     if (row < m_height)
  73.         return (uchar*)(data() + (row * m_channels * m_width));
  74.     else
  75.         return (uchar*)data();
  76. }
  77.  
  78. void RawImage::setAlpha(int x, int y, int alpha)
  79. {
  80.     uchar *d;
  81.     if ((y < m_height) && (x < m_width))
  82.     {
  83.         d = (uchar*)(data() + (y * m_channels * m_width) + (x * m_channels));
  84.         d[m_channels-1] = alpha;
  85.     }
  86. }
  87.  
  88.  
  89. QImage RawImage::convertToQImage(bool cmyk, bool raw)
  90. {
  91.     int chans = channels();
  92.     QImage img = QImage(width(), height(), QImage::Format_ARGB32);
  93.     QRgb *ptr;
  94.     uchar *src;
  95.     uchar cr, cg, cb, ck, ca;
  96. //	img.create(width(), height(), 32);
  97.     if (raw)
  98.     {
  99.         for (int i = 0; i < height(); i++)
  100.         {
  101.             ptr = (QRgb *)img.scanLine(i);
  102.             src = scanLine(i);
  103.             for (int j = 0; j < width(); j++)
  104.             {
  105.                 *ptr++ = qRgba(src[0],src[1],src[2],src[3]);
  106.                 src += chans;
  107.             }
  108.             qDebug() << "## raw line -> " << i;
  109.         }
  110.     }
  111.     else
  112.     {
  113. //		img.setAlphaBuffer( true );
  114.         for (int i = 0; i < height(); i++)
  115.         {
  116.             ptr = (QRgb *)img.scanLine(i);
  117.             src = scanLine(i);
  118.             for (int j = 0; j < width(); j++)
  119.             {
  120.                 if (chans > 1)
  121.                 {
  122.                     if (cmyk)
  123.                     {
  124.                         ck = src[3];
  125.                         cr = 255 - qMin(255, src[0] + ck);
  126.                         cg = 255 - qMin(255, src[1] + ck);
  127.                         cb = 255 - qMin(255, src[2] + ck);
  128.                         if (chans > 4)
  129.                         {
  130.                             ca = src[4];
  131.                             *ptr++ = qRgba(cr,cg,cb,ca);
  132.                         }
  133.                         else
  134.                             *ptr++ = qRgba(cr,cg,cb,255);
  135.                     }
  136.                     else
  137.                     {
  138.                         if (chans > 3)
  139.                             *ptr++ = qRgba(src[0],src[1],src[2],src[3]);
  140.                         else
  141.                             *ptr++ = qRgba(src[0],src[1],src[2],255);
  142.                     }
  143.                 }
  144.                 else
  145.                     *ptr++ = qRgba(src[0],src[0],src[0],255);
  146.                 src += chans;
  147.             }
  148.  
  149.             //////qDebug() << "## n line -> " << i;
  150.  
  151.         }
  152.     }
  153.     return img;
  154. }
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wath is your source data tiff?