(fast!) 2D rotation and scaling for grayscale bitmaps

I need  source code (DELPHI or C) to implement a rather fast method to rotate a grayscale image about small angles (+-3 degrees) and scale it down using antialias. Have found nothing acceptable yet
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hlavaConnect With a Mentor Commented:
try write for each pixel code like(in math):


xx-result x
yy-result y
xb-start x
yb-start y

if you can use rotation about one point you must get this point to 0,0 and then rotate

shifting code(math):

good luck!!

a method to rotate an image on the web, i would use JavaScript. The images are rotated already with a tool like Photoshop.
Rotating can be done with the following script:

 if (document.images != null) {
     single0 = new Image();single0.src  = "images/aboutstar_0.gif";
     single1 = new Image();single1.src  = "images/aboutstar_1.gif";
     single2 = new Image();single2.src  = "images/aboutstar_2.gif";
     single3 = new Image();single3.src  = "images/aboutstar_3.gif";
     single4 = new Image();single4.src  = "images/aboutstar_4.gif";
     single5 = new Image();single5.src  = "images/aboutstar_5.gif";
     single6 = new Image();single6.src  = "images/aboutstar_6.gif";
     single7 = new Image();single7.src  = "images/aboutstar_7.gif";
     single8 = new Image();single8.src  = "images/aboutstar_8.gif";
     var singleI = 0, singleInTimeout = singleOutTimeout = null;

 function fadeInabout() {
     if (document.images != null && singleI < 8) {
         document.images['single'].src = eval('single' + (++singleI) + ".src");
         singleInTimeout = setTimeout('fadeInabout()',60);

function thisfirst() {
   if (singleI >= 8) {


<IMG SRC="images/aboutstar_0.gif" NAME="single" BORDER="0">
<A HREF="pagina_01.html" TARGET="Right" onMouseover=thisfirst();fadeInabout()>  
About Star</A>

arnolduAuthor Commented:
This is a wonderful idea - if rotating images on the web had been the actual question. I obtain images from the scanner and have to correct misalignments etc. and rotate them by small angles (e.g. 0.3 °)
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Why don't u use a tool like Photoshop or a shareware program like paintshop pro then?
arnolduAuthor Commented:
Because I dont have them statically ! My application scans images using a self-written twain interface and I need a kind of preprocessor within my own program to correct for smaller misalignment errrors.

Perhaps it is an idea to post the question in another place then, like in programming C / C++
Good luck!
how about composing sheer transforms?
arnolduAuthor Commented:
Good idea - but how to implement them with interpolation?
I found this reference in
Subject 3.01: How do I rotate a bitmap?

    The easiest way, according to the comp.graphics faq, is to take
    the rotation transformation and invert it. Then you just iterate
    over the destination image, apply this inverse transformation and
    find which source pixel to copy there.

    A much nicer way comes from the observation that the rotation

        R(T) = { { cos(T), -sin(T) }, { sin(T), cos(T) } }

    is formed my multiplying three matrices, namely:

        R(T) = M1(T) * M2(T) * M3(T)


        M1(T) = { { 1, -tan(T/2) },
                  { 0, 1         } }
        M2(T) = { { 1,      0    },
                  { sin(T), 1    } }
        M3(T) = { { 1, -tan(T/2) },
                  { 0,         1 } }

    Each transformation can be performed in a separate pass, and
    because these transformations are either row-preserving or
    column-preserving, anti-aliasing is quite easy.


    Paeth, A. W., "A Fast Algorithm for General Raster Rotation",
    Proceedings Graphics Interface '89, Canadian Information
    Processing Society, 1986, 77-81
    [Note - e-mail copies of this paper are no longer available]

    [Gems I]
[Gems I]
    Graphics Gems,
    Andrew Glassner (ed.), Academic Press 1990, ISBN 0-12-286165-5

You could quite easily enlarge a "working window" on the
original picture, skew this according to the angle you want to
rotate and scale it down to the desired size. Antialiasing can
be done in this last step without problems.

I happen to have the Graphics Gems article with me now.
It's too long (and too copyrighted) to type in here, but for the next week or so (until the owner of the book wants it back)
I may be able to answer any furthur questions you have on it.
The article also compares a similar technique  that does a 2 pass simultaneous shear and scale.
A.R. Smith (1987) "Planar 2-Pass Texture Mapping and Warping"
ACM Computer Graphics (SIGGRAPH). 21(4), 263-272.
(A Fast Algorithm for General Raster Rotation)
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