"Walter Dnes" on wrote...
| I'm preparing a little blurb on binning as a way of reducing high-ISO
| noise. I was going through some of the math, and came up with a
| surprise, which may or may not mean anything in the real world...
|
| Step 1) Start with an 8-bit-per-channel tiff file.
|
| Step 2) This step deliberately left blank<g>.
|
| Step 3) Bin the image using 2x2 grids. I.e. average 4 adjacent pixels
| to create a pixel in the output image.
|
| In base_2 "decimal point" format, the averaged value for each pixel
| looks like binary xxxxxxxx.xx where "x" is either 0 or 1. This is due
| to the fact that averaging amongst 4 pixels means dividing by 4. Since
| we're dealing with an 8-bit tiff for output, the final result is
| xxxxxxxx, which throws away some of the information.
|
| Now let's go back, and insert a command at step 2. Let's "convert"
| the image to a 16-bit-per-channel tiff. Instead of using 100% of 8-bit
| colourspace, we're using 1/256th of 16-bit colourspace. The initial
| values are all in the form binary xxxxxxxx00000000. The final result,
| after step 3, will now be binary xxxxxxxxxx000000. In other words,
| we've traded off image size for additional colours. I don't have a
| video card or monitor or driver than can show more than 8 bits per
| channel. I don't know the answer to the following questions...
|
IM saves all image data as 16 bit internally if it is Q16.
It of course throws way the lower bits if it saves to 8bit.
Note that #FFFF => #FF both are white
Throwing away bits only reduces the quailty, but not the resulting
colors (other than quality effects).
I would ignore it.
| 1) Does it produce a noticeable difference, assuming you have the
| necessary hardware and software to display more than 8 bits per channel?
|
nope.
| 2) If the answer to 1) is "yes", is the result an improvement over 8
| bit colour?
|
only in terms of final quality.
| My binning script follows. I call it "binn". It's invoked like so...
| binn source_file output_file bin_factor
|
Note for IM examples, you need to show the basic idea, not a script to
do the job. Only if the job becomes extremely complex with lots of
seperate command should you refer to an actual script.
By all means point out scripts though.
Anthony Thyssen ( System Programmer ) <[EMAIL PROTECTED]>
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