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Entering specific RGB values to calculate pixel counts

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John McCready
Entering specific RGB values to calculate pixel counts
on Jan 20, 2010 at 7:51:54 pm

I have an entire series of images and was wondering if I could enter a fixed set RGB values some where and see a total pixel count for each one of them.

When I go to foreground color and enter the RGB values there and then set the color range to zero and press OK, I get a Warning: No pixels were selected message.

Any additional advice that you have would be much appreciated.

Thanks, jmccread



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Mike Gondek
Re: Entering specific RGB values to calculate pixel counts
on Jan 21, 2010 at 1:43:03 am

Color range can give you a selection, but not a count of pixels. Even if you set the fuzziness down to zero color range will select more pixels than the EXACT value in your foreground color

Another post about medical research about 8 down suggests using blobfinder, give that a try:
http://www.cb.uu.se/~amin/BlobFinder/index.htm


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John McCready
Re: Entering specific RGB values to calculate pixel counts
on Jan 21, 2010 at 1:58:11 pm

Mike:

Just curious about your comment that PhotoShop CS4 is not very accurate at calculating pixel counts using the color range tool. Has there been a lot of concern about this?

As you have suggested, I have registered at the BlobFinder site to to get a password to download and install the password.

Thank you for your advise,

John





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Mike Gondek
Re: Entering specific RGB values to calculate pixel counts
on Jan 25, 2010 at 11:14:41 pm

I did not mean that Photoshop is not accurate in counting pixels, but that color range cannot be set to choose exactly the value of your target color adn no other color.

For example if your foreground color is 255R 255G 255B and you do a color range selection with fuzziness set to 0, color range will not only select the exact color of 255R 255G 255B, but also colors close to that value if they exist in your document.


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Theo van Laar
Re: Entering specific RGB values to calculate pixel counts
on Jan 27, 2010 at 1:31:40 pm

"Color range can give you a selection, but not a count of pixels. Even if you set the fuzziness down to zero color range will select more pixels than the EXACT value in your foreground color

Another post about medical research about 8 down suggests using blobfinder, give that a try:
http://www.cb.uu.se/~amin/BlobFinder/index.htm"


Blobfinder is used to automaticly recognize and count blobs like fluorescent spots in a tissue, derived from immunofluorescency or the qPCR-based PLA.
To calculate the area (which is "the number of pixels") of a staining (like e.g. the area of bloodvessels in a tissue measured by CD31 staining), a program like ImageJ is more suitable:

http://rsbweb.nih.gov/ij/download.html

Theo


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