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Replies:
8
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Last Post:
Apr 19, 2006 7:48 AM
by: husenful
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Contrast Example
Posted:
Mar 7, 2006 10:30 PM
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I am a semi-newbie to JAI. I have been pouring over all of the examples and searching the internet like a madman. Does anyone have a clear example of how to do contrast? I have heard a lot of different methods (lookup table multiplying bands by constant, the rescale operation, etc). I am basically looking for something simple that runs very fast. I need to provide a slidebar control that will allow a user to adjust the contrast easily.
If someone could help me out here I would be eternally grateful.
Thank you.
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Re: Contrast Example
Posted:
Mar 8, 2006 6:13 AM
in response to: foxdeath
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A very, but not extremly valid option for enhancing the contrast is by simply taking the average of the RGB values and doing the following
a = (r + g + b) / 3
c = floating point value between 0 and finite, though I'd set 2 or 3 as top, where 1 = no change
r = a + (r - a) * c;
g = a + (g - a) * c;
b = a + (b - a) * c;
thats all. By specifying c > 1 you'll get more color, and < 1 it'll turn more grayish.
hope it helps.
Two variations:
- setting 'a' as the middle of your color range, so if your color ranges between 0 and 1, you'd set 'a' to 0.5. While if it was between 0 and 255, it'd be 127.
- setting a to the average of several neigbouring pixels. This would be more like a local contrast increase.
Both these options also work for grayscale, while the first mentioned does not.
edit: Added the 2 variations.
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Re: Contrast Example
Posted:
Mar 8, 2006 7:58 AM
in response to: foxdeath
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i think you can use the "rescale" method. it directly affects the contrast value.
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Re: Contrast Example
Posted:
Mar 8, 2006 11:08 AM
in response to: foxdeath
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Thank you very much, that was exactly what I was looking for. Here is the final code that I came up with. It is a very simple way of implementing contrast that runs very quickly. I hope others can use it:
public static PlanarImage setColor(PlanarImage source,
int red, int green, int blue,
float contrast,
float brightness)
{
// Time the process for performance
long beginTime = (new java.util.Date()).getTime();
// Setup the parameter block for the source image and
// the three parameters for the mean operation
ParameterBlock mpb = new ParameterBlock();
mpb.addSource(source); // The source image
mpb.add(null); // null ROI means whole image
mpb.add(1); // check every pixel horizontally
mpb.add(1); // check every pixel vertically
// Perform the mean operation on the source image
PlanarImage meanImage = JAI.create("mean", mpb, null);
// Retrieve the mean pixel value
double[] mean = (double[])meanImage.getProperty("mean");
// Average the mean of all bands
double sum = 0.0D;
for (int i=0; i < mean.length; i++)
{
sum += mean]]]]]]]]]]
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Re: Contrast Example
Posted:
Mar 8, 2006 3:19 PM
in response to: foxdeath
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Often people add the brightness first and then caculate the contrast. Try it. You'll notice that when you increase the brightness by 20% and the contrast by 40% that it will get really more depth, while if you do the contrast first and then the brightness it'll just get foggy. Anyway, I'm glad I helped.
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Re: Contrast Example
Posted:
Apr 19, 2006 2:01 AM
in response to: foxdeath
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Todd,
Thanks for your code.
What's the clamp method you're referring to ?
Thanks,
Yann.
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Re: Contrast Example
Posted:
Apr 19, 2006 5:48 AM
in response to: yleguern
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The clamp method just makes sure the value is an integer between 0 and 255 and then converts it to a byte. Thats all... Glad the code helped. I appreciated the help that I received and that is why I return the favor my posting my code.
Enjoy!
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Re: Contrast Example
Posted:
Apr 19, 2006 6:34 AM
in response to: foxdeath
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Ok, now I understand : all occurrences of arrays : [ i] was interpreted as "Italic" by the forum and disappeared from the source.
thanks again
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Re: Contrast Example
Posted:
Apr 19, 2006 7:48 AM
in response to: foxdeath
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the following example works also very fine and returns results incl. brightness-adjustment, very similar to photoshop "Brightness/Kontrast"...
PlanarImage contrast(PlanarImage myImage, int level, float boost) {
long beginTime = (new java.util.Date()).getTime();
// pre-adjust Brightness to set a centre for continuative contrast-modifications
if (level != 0) {
try {
if (level < -255) level = -255;
if (level > 255) level = 255;
double[] constants = {(float)level, (float)level, (float)level};
ParameterBlock pb = new ParameterBlock();
pb.addSource(myImage);
pb.add(constants);
myImage = JAI.create("addconst", pb, null);
} catch (Exception e) {
e.printStackTrace();
return myImage;
}
}
// start contrast
try {
int numBands = myImage.getNumBands();
// bp is used to compress or pull colorrange
// bp = BoostPixel 
float[][][] bp = new float[numBands][2][];
// decrease contrast
if (boost < 0) {
if (boost < -127.5F) boost = -127.5F;
boost = 127.5F + boost;
float innerMax = (255.0F / ]]]]]] 127.5F) boost = 127.5F;
boost = 127.5F - boost;
float innerMax = (255.0F / 2.0F) + boost;
float innerMin = (255.0F / 2.0F) - boost;
for (int i = 0; i < numBands; i++) {
bp[!! i !!][0] =]]]]
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