Re: Scale a vector

Peter Duniho wrote:
Matteo Migliore wrote:
[...]
But no, I need to resize a one-dimensional array.

For what it's worth, you still haven't provided any guidance regarding
_how_ you want the data in the array to be calculated. Is that
because you yourself do not know?

I arrived to the conclusion that I can use the straight line equation
to interpolate value in X1 to X2 and value X3 to X4 etc... If the size parameter
is greater than the width of the original bitmap.

[...]
This function calculate the middle luminance for each column (X
coordinate) in the image and return an array of middle luminances,
so the array lenght is the width of the image.

Same thing for the vertical projection, but the calculate is on rows!

Ok, now I've to compare horizontal RGB projection for image A, B and
C. The array lenght must be the same, so I've to scale RGB proj. of A to
100 elements,
RGB proj. of B to 100 elements and the same for C. 100 is random
selected, it could be 640
(the most minum width for an image). If the image width is smaller
than 100px the function must
Scale the array to 640.

I am not clear on what you mean by "middle". But, whether that's the
median value of the column or row of pixels, the average, or literally
the value of the middle pixel, I think the solution is basically the
same.

Sorry, I mean the median luminosity value for each column for horizontal RGB
and for each row for vertical RGB.

What you are looking for is essentially a one-dimensional image
scaling. So, a couple of thoughts come to mind:

1) You may find that it makes more sense to scale the input
bitmaps first, and then do the comparison on data calculated from the
scaled input. This is less efficient because you wind up scaling
data that you don't necessarily use, but

a) it's not clear even now from your description that you
really don't want to use the data (even though you may believe that
you don't, it's possible that because you are scaling your data, you
really do want the scaling to take into account all neighboring pixels, not
just those in a specific direction), and

b) because it makes the implementation of your solution
simpler, the reduced efficiency may be a worthwhile price for simpler
code.

No I can't scale images beacuse performance are the key,
so I've to scale arrays and store thay in a Dictionary to compare they.

So I can't resize images, that was my first idea :-).

2) If you don't want to scale the input first, I would say that
instead of treating the data as an array, you should generate new
bitmaps, as wide or high as the input bitmap, and one pixel in size in
the other direction. This way, you can take advantage of the built-in
.NET image processing functionality. How best to do this would depend
on what is meant by "middle".

In option #2, if you are literally taking a the middle pixel from a
column or row, then you should just copy a complete row or column
(respectively) of pixels into a new bitmap and then scale that bitmap
and extract the luminosity from the resulting bitmap. If you have
some other meaning of "middle", you'll have to convert your
luminosity data into a format that can be treated as a regular Bitmap
instance (for example, a plain 24-bit-per-pixel RGB Bitmap, where
each pixel is a gray value based on the lumonisity value). Then you
just scale that bitmap in a single dimension and extract back out the values (which should
still be gray values, making it trivial to convert back to
luminosity).
In either case, the scaling will be done with the Bitmap and Graphics
classes. You'll create two Bitmap instances: the input one and the
output one. Then you'll use Graphics.FromImage() to get a Graphics
instance for the output Bitmap instance. Then you'll use the
Graphics.DrawImage() method to copy the data from the input Bitmap to
the output Bitmap, providing source and destination rectangles that
correspond to the full size of the input and output Bitmaps,
respectively. The DrawImage() method will then apply some
image-scaling algorithm to the data; which one is specifically used
will depend on the InterpolationMode property of the Graphics
instance used for the drawing.

No I can't :-). So I've to scale the arrays (I know, I'm repetitive :-D)

The straight line equation and interpolation is a good mode,
but it not simple. But I think that is the only way :-(.

I found this article on CodeProject:
http://www.codeproject.com/useritems/Douglas-Peucker_Algorithm.asp

This algorithm solve a problem similar to mine, but it only
*reduce* points number and accept a tollerance parameter, not how many points
to have :-(.

Hope that helps.

Pete

I don't know how to thank you!!
(But my problem remain).

I'll upload my solution on CodePlex ;-)

It's an application to find duplicated images :-D
Matteo Migliore.

.

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