image brightness (damn, me again)

[Rainer M. Engel]

hey there..

I remember me asking that question or reading the answer to that already
before.

I have the same image in different color (bit-depth) modes.

cat1 (RGB, 8bit)
https://dl.dropboxusercontent.com/u/414433/imagej/brightness/cat1.png

cat2 (RGB, 16bit)
https://dl.dropboxusercontent.com/u/414433/imagej/brightness/cat2.png

cat3 (grayscale, 16bit)
https://dl.dropboxusercontent.com/u/414433/imagej/brightness/cat3.png

What kind of correction is automatically done when converting the RGB to
i.e. 8bit/16bit in ImageJ. The grayscale cat is already brighter than in
other graphics environments we use.
I Remember some kind of range thing..


Best Regards,
Rainer



--
Rainer M. Engel, Dipl. Digital Artist
scientific|Media GbR
Pichelsdorfer Str. 143
13595 Berlin

--
ImageJ mailing list: http://imagej.nih.gov/ij/list.html

[Michael Schmid]

Hi Rainer,

RGB to 8-bit grayscale conversion calculates

  rWeight*R + gWeight*G + bWeight*B

where R, G, B are the pixel values of the colors (0.255 range) and the weights are either 1/3 each or 0.30, 0.59, 0.11, depending on the setting in Edit>Options>Conversion.

The weights sum up to 1, so grayscale values are unaffected when converting RGB to 8-bit grayscale and vice versa.

Conversion form RGB or 8-bit grayscale to 16 bits simply leaves the 8-bit grayscale values unchanged. ImageJ automatically adjust the displayed grayscale range for 16-bit images to the range from the minimum to the maximum pixel value. To make the 16-bit image resulting from conversion appear on the screen as the original 8-bit or RGB image, use 'Set' in the 'Brightness&Contrast' panel and set the range to 0-255.

There is also the 'scale' option in the Edit>Options>Conversion panel. As far a I remember, this one affects only conversion to lower bit depth, e.g. 16-bit to 8-bit or RGB (which has 8 bits/color). With that option on, the currently displayed range (what you see in 'Set' of the B&C panel) is mapped onto the 8-bit range of 0-255.

---

If your image looks different in ImageJ than in some other software, that other software uses color management, i.e., a color profile, either from the file or built into that program.  ImageJ just put the pixel values as they are to the display, without any color management.  (There may be additional correction for the screen's Gamma and other settings in the operating system or the screen itself; these of course affect all programs including ImageJ.)

Hope this helps,

Michael
________________________________________________________________
On Jun 21, 2013, at 16:21, Rainer M. Engel wrote:

> hey there..
>
> I remember me asking that question or reading the answer to that already
> before.
>
> I have the same image in different color (bit-depth) modes.
>
> cat1 (RGB, 8bit)
> https://dl.dropboxusercontent.com/u/414433/imagej/brightness/cat1.png
>
> cat2 (RGB, 16bit)
> https://dl.dropboxusercontent.com/u/414433/imagej/brightness/cat2.png
>
> cat3 (grayscale, 16bit)
> https://dl.dropboxusercontent.com/u/414433/imagej/brightness/cat3.png
>
> What kind of correction is automatically done when converting the RGB to
> i.e. 8bit/16bit in ImageJ. The grayscale cat is already brighter than in
> other graphics environments we use.
> I Remember some kind of range thing..
>
>
> Best Regards,
> Rainer
>
>
>
> --
> Rainer M. Engel, Dipl. Digital Artist
> scientific|Media GbR
> Pichelsdorfer Str. 143
> 13595 Berlin
>
> --
> ImageJ mailing list: http://imagej.nih.gov/ij/list.html

--
ImageJ mailing list: http://imagej.nih.gov/ij/list.html

[Rainer M. Engel]

Hello Michael,

that sounds more like an explanation to me. Thank you for providing me
the needed tips to work around..

Big help.
Best regards,
Rainer


Am 21.06.2013 19:01, schrieb Michael Schmid:

> Hi Rainer,
>
> RGB to 8-bit grayscale conversion calculates
>
>   rWeight*R + gWeight*G + bWeight*B
>
> where R, G, B are the pixel values of the colors (0.255 range) and the weights are either 1/3 each or 0.30, 0.59, 0.11, depending on the setting in Edit>Options>Conversion.
>
> The weights sum up to 1, so grayscale values are unaffected when converting RGB to 8-bit grayscale and vice versa.
>
> Conversion form RGB or 8-bit grayscale to 16 bits simply leaves the 8-bit grayscale values unchanged. ImageJ automatically adjust the displayed grayscale range for 16-bit images to the range from the minimum to the maximum pixel value. To make the 16-bit image resulting from conversion appear on the screen as the original 8-bit or RGB image, use 'Set' in the 'Brightness&Contrast' panel and set the range to 0-255.
>
> There is also the 'scale' option in the Edit>Options>Conversion panel. As far a I remember, this one affects only conversion to lower bit depth, e.g. 16-bit to 8-bit or RGB (which has 8 bits/color). With that option on, the currently displayed range (what you see in 'Set' of the B&C panel) is mapped onto the 8-bit range of 0-255.
>
> ---
>
> If your image looks different in ImageJ than in some other software, that other software uses color management, i.e., a color profile, either from the file or built into that program.  ImageJ just put the pixel values as they are to the display, without any color management.  (There may be additional correction for the screen's Gamma and other settings in the operating system or the screen itself; these of course affect all programs including ImageJ.)
>
> Hope this helps,
>
> Michael
> ________________________________________________________________
> On Jun 21, 2013, at 16:21, Rainer M. Engel wrote:
>
>> hey there..
>>
>> I remember me asking that question or reading the answer to that already
>> before.
>>
>> I have the same image in different color (bit-depth) modes.
>>
>> cat1 (RGB, 8bit)
>> https://dl.dropboxusercontent.com/u/414433/imagej/brightness/cat1.png
>>
>> cat2 (RGB, 16bit)
>> https://dl.dropboxusercontent.com/u/414433/imagej/brightness/cat2.png
>>
>> cat3 (grayscale, 16bit)
>> https://dl.dropboxusercontent.com/u/414433/imagej/brightness/cat3.png
>>
>> What kind of correction is automatically done when converting the RGB to
>> i.e. 8bit/16bit in ImageJ. The grayscale cat is already brighter than in
>> other graphics environments we use.
>> I Remember some kind of range thing..
>>
>>
>> Best Regards,
>> Rainer
>>
>>
>>
>> --
>> Rainer M. Engel, Dipl. Digital Artist
>> scientific|Media GbR
>> Pichelsdorfer Str. 143
>> 13595 Berlin
>>
>> --
>> ImageJ mailing list: http://imagej.nih.gov/ij/list.html
>
> --
> ImageJ mailing list: http://imagej.nih.gov/ij/list.html
>
>

--
ImageJ mailing list: http://imagej.nih.gov/ij/list.html