http://imagej.273.s1.nabble.com/24-bit-RGB-to-16-bit-gray-conversion-tp3704473p3704477.html
that is looking good. However, I am unable to run your macro. I get the
and pasted your code in and then tried to run it - without succes. I did
> The following macro converts an RGB image with 16.7 million possible
> colors into a 32-bit image with 16.7 million possible gray values.
> Convert the 32-bit image to 16-bits and you get an image with 65536
> possible gray values.
>
> if (bitDepth!=24)
> exit("RGB image required");
> setBatchMode(true);
> w = getWidth;
> h = getHeight;
> rgb = getImageID;
> newImage("32-bit", "32-bit", w, h, 1);
> float = getImageID;
> for (y=0; y<h; y++) {
> showProgress(y, h);
> for (x=0; x<w; x++) {
> selectImage(rgb);
> v = getPixel(x,y)&0xffffff;
> selectImage(float);
> setPixel(x, y, v);
> }
> }
> resetMinAndMax;
> setBatchMode(false);
> //run("16-bit");
>
> -wayne
>
> On Nov 14, 2005, at 5:10 PM, ij-Newsgroup wrote:
>
>> Thanks for your suggestions!
>>
>> However, I still feel like having lost more information than I wanted
>> to.
>>
>> If I look at the histogram of either red, blue or green channel, then it
>> looks like a comb when converting from 8bit to 16bit (obviously) and
>> after adding the 3 channels, I again end up with a comb-like histogram
>> that uses only 256 (or less) of the 65535 possible colours. So in short,
>> I have gone from 16 million colours to 256 shades of gray and not to
>> 65535 as intended.
>>
>> What I want to do is to convert the 16 million colours into 65535 levels
>> of gray WITHOUT chopping it down to 256 colours in any of the
>> intermediate steps.
>>
>> This is for a densitometry application for which the response of the
>> eye is not relevant, but it is important to destinguish more than 256
>> different gray values to quantify the staining accurately.
>>
>> I understand that 24bit means 3 times 8 bit, hence 8 bit per colour
>> (red, blue, green) and that 8 bit allow 256 histogram channels and hence
>> 256*256*256=16,777,216 result in 16.7 million colours. But that still
>> somehow does not fully convince me that I can only obtain 256 different
>> gray values. If I use different weights for each colour channel (as
>> suggested by one of you) then the resulting sum of the 3 split images
>> would not give me the honeycomb structure in the histogram, but
>> weighting colours by the wavelength-dependent sensitivity of the human
>> eye may not be adequate for my application.
>>
>> Any more comments?
>>
>> Thanks,
>> Art
>>
>>
>>
>> Robert Rohland wrote:
>> > Art -
>> >
>> > Not too difficult. Gray scale is just the average of the red,
>> green, and
>> > blue channels. If you have 16 bits (65,536 levels) to work with,
>> you can
>> > simply add the red, green, and blue channels and scale them up however
>> > you like.
>> >
>> > Here's how to do one manually:
>> >
>> > I just opened the baboon.jpg, a 24-bit RGB. Select the baboon window.
>> > Then select the menu command Image / Color / RGB Split. The colorful
>> > baboon will go away and you will see three new windows entitled
>> > baboon.jpg (red), baboon.jpg (green), and baboon.jpg (blue). Each is
>> > 8-bit gray scale.
>> >
>> > First, you have to convert each of these 8-bit (256 levels) images to
>> > 16-bits (65536 levels). Select "baboon.jpg (red)." Select menu command
>> > Image / Type / 16-bit. Do the same with the green and blue 8-bit
>> > channels. Converting to 16-bits before doing math will prevent
>> overflow.
>> >
>> > Now select menu command Process / Image Calculator. In the dialog box,
>> > select "baboon.jpg (red)" for Image1, "Add" for Operation, and
>> > "baboon.jpg (green)" for Image2. Check the "Create New Window"
>> checkbox
>> > and hit OK.
>> > You will get a new window entitled "Result of baboon.jpg," which
>> will be
>> > a 16-bit result.
>> >
>> > Now run the Image calculator again to add in the "baboon.jpg (blue)"
>> > layer. You will a new image called "Result of Result." This is your
>> > 16-bit grayscale image. Since you just added three 256-level images
>> > together, the maximum will be 765. You can scale this up by selecting
>> > menu command Process / Math / Multiply. A dialog box will ask you for
>> > the multiplier. The biggest multiplier you can use is 85 before you
>> > overflow the 16-bit maximum of 65535.
>> >
>> > If you need to adjust the brightness and contrast, use Image /
>> Adjust /
>> > Brightness/Contrast.
>> >
>> > If you have a whole bunch of pictures to do, make a macro using this
>> > sequence of commands.
>> >
>> > - Robert M. Rohland
>> >
[hidden email]
>> >
[hidden email]
>> > 146 Garner Circle
>> > Montrose MN 55363
>> > 763-675-8905
>> > 612-226-9735 (cell)
>> >
>> > ----- Original Message ----- From: "ij-Newsgroup"
>> > <
[hidden email]>
>> > To: <
[hidden email]>
>> > Sent: Sunday, November 13, 2005 3:54 PM
>> > Subject: 24 bit RGB to 16 bit gray conversion?
>> >
>> >
>> >> Does anyone know how to convert a 24 bit RGB image (16.7 million
>> >> colours) into a 16 bit grayscale image?
>> >>
>> >> Thanks
>> >> Art
>>
>> --
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