A friend asked me this question:<br><br><blockquote><font size=1>In reply to:</font><hr><p>Is there any way to tell in photoshop to get pixel quantities for a certain color?<br><br> I have a gif and what I would like to know is how many pixels are black is there any automated way to find that? I doubt it but figured it couldn't hurt to ask.<p><hr></blockquote><p><br>Thanks<br><br>my photos
I don't know of any way to count actual pixels of one particular color. I doubt that there's a feature for that, because I can't think of a single reason why your friend would want to. You could tell him to zoom in real close and count manually, but that could take a while! <br><br>The Graphic Mac for your Mac and graphics news, tips and more.
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I would ask the same question, why? There are ways to do it and if you wanted to set up to do it to thousands of images then there is scientific software out there to count them. But this won't be cookbook. You could start with low end stuff and google "NIH image" and see what people have added on or extended that program. Then google "image density" and there might be something.<br><br>Do they really want a count or do they want a histogram slice through the picture? Density comparisons have more information than a simple count. (Which isn't so simple.)<br><br> I would think a better question is, "does this picture have more black than this other one?" This can easily be done by comparing the histograms. Or select black and remove all other color.<br><br><br><P ID="edit"><FONT SIZE=-1><EM>Edited by polymerase on 01/15/08 07:48 AM (server time).</EM></FONT></P>
Loc: United States
How many pixels in the color black - is that what he's asking?<br><br>Pixels aren't dependent on the color your using, they rely on the size of the image - go under 'Image Size' in Photoshop's menu and you'll see the pixel size right there...<br><br><br><br>[color:purple]Work With ____! </font color=purple>
Here is more info:<br><br>The reason why is that my image is basically a blank map that is filled as you climb peaks and the blank area essentially corresponds to a geographic area. See this map for Oregon for a general idea:<br><br>http://www.pbase.com/ericnoel/image/68896145<br><br>For purposes of the hobby, it would be quite handy if I could get an approximation of each area in pixels and then extrapolate geographic area from that. I figure I could paint each area with a unique color not found elsewhere in the image and then record that number if there were some way to find it. I do know that when you use SAVE FOR WEB that it orders the pixels colors by popularity or how often they appear if you desire. So somewhere Photoshop is or can calculating that info which is where my question came from. <br><br><br>my photos
Loc: United States
Um....huh?<br><br>If he's looking to fill each area with a unique color, tell him to use the magic wand, click anywhere inside the border of the shapes, and fill it with whatever color he wants.<br><br>This business of counting the pixels seems like a wasted exercise. I'm still not clear on what exactly he wants to do.<br><br><br><br>[color:purple]Work With ____! </font color=purple>
Let me get this straight: what you want to do is for a given map (which is an image doc), calculate the area of the 'visited' parts, which have been coloured in a single solid colour, by using the pixel count for that colour or colours in the map image and calculating geographic area on the basis of 'n kmsq/pixel' or whatever. So you end up with a map image, and a figure that says e.g.: red visited area on this map=300 pixels=15kmsq visited.<br><br>As I understand it, your problem is not anything to do with getting the pixels onto the map, it's all about calculating the area/pixelcount of a particular colour that represents a geographical area visited, yes?<br><br>(I've no idea how to do this, I'm just trying to clarify the question so that someone else can try to answer it )<br><br>- padmavyuha<br><br>[color:purple]A lopsided man runs best along the little side-hills of success<br>- Frank Moore Colby</font color=purple>
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Ah, you want to delineate a specific area and measure the area. Google for "NIH Image" which is a National Institutes of Health program which does this as a menu item. I think you can calibrate it and it will give you square feet of a non regular shape. It will help find the edges too. <br><br>I have not used the program in years and do not know what upgrade path there is. I do know people are still using it to measure gels. It may have upgraded to another program or multiple programs.<br><br>The program is free. If it does not exist there has to be free replacements since this is a common scientific application.<br><br>Claim to fame: I had some input into some of the preprogramming that went into this in the early 80s. I needed to measure plasmids on electron micrographs and was using an Apple IIe and a tablet with clicking cursor which sat underneath a negative enlarger. Pretty much what you want to do except I was doing perimeter instead of area.<br><br>
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