How do I make measurements in Photoshop

[pgk]

I've been working on British and Irish Gobies for some time. Some are very difficult to differentiate (or rather define the differentiation of). I'm wondering if there are any tools/plug-ins which will enable me to make 'relative' measurements in Photoshop? Sometimes these would be of curved details (such as fin rays) which I need to measure the size of relative to the fishes' total length or another defined size. I'm using CS4 at the moment and any thoughts would be much appreciated. If this doesn't make good sense then I can post a couple of images showing what I need to measure.

These creatures measure from 2~30cm fully grown depending on species, so roughly fall within macro sizing.

[Charles Krebs]

Paul,

Straight lines are easy. Curved not quite as straightforward. I've seen some expensive "scientific" software that (if I recall correctly) can be used with Photoshop for many measuring functions. (Reindeer Graphics is one). I would think ImageJ would have this ability. And there are likely many other solutions I am not aware of.

But if you know the magnification at which the image was photographed, or (perhaps even better) if you can include an object of known size in the picture (a ruler, a coin... just about anything where you know a linear dimension) then there's an inexpensive program called "Universal Desktop Ruler" (http://avpsoft.com/) that can be very effectively used to do this. It can measure the length of a line in pixels (curves must be "entered" by clicking along in small straight line sections) and this measurement can be "calibrated" to a scale of your own. Then it will "read-out" in both pixels and in your units as well. It's not a PS plug-in, but can be brought up to measure anything that is displayed on screen.

[g4lab]

If you already have CS4 then Fovea Pro from Reindeer Graphics is the only thing to think about.

It does things that are amazing. Many things it does much better than software costing literally twenty times as much.

go to www.drjohnruss.com to read and download a lot of info on it.
Dr, Russ gives lots of stuff away free. There is a great pdf on Stereology.

If you like to program you can get all the same functionality for much less money in Reindeer's Image Processing Toolkit. You have to compile9C or C++ I think) the programs but they give you all the source code you need. IPTK is a book that you can get at university libraries so you might be able to get the disk from the book and compile only the functionality that you need.

Most of the functionality comes up as plug ins for PhotoShop and will work from PS 7 to the current edition.

I think the plug ins might also work in Image Pro from Media Cybernetics

[Charles Krebs]

Gene

If you already have CS4 then Fovea Pro from Reindeer Graphics is the only thing to think about.

Well, you may need to think about your credit card limit too

It's first rate, but if all that is desired is to get linear measurements from pictures then $ 250 (IPTK 5.0) to $800 (FoveaPro4) may be more than is really needed.

[g4lab]

I meant Reindeer Graphics not necessarily only Fovea Pro
But FP rocks!!

[Craig Gerard]

What about Photoshop Extended Version. Doesn't it have additional tools for such purposes? I haven't used such tools, so I can't really comment; just add another possible suggestion.

Craig

[elf]

Take a look at Paths in PS. They should be able to give you the length info you need.

[pgk]

Many thanks for all your replies. I'm looking at all the suggestions and will try to get my head around the relative merits of each. I should have said that I'm mac based. Also one of the problems is that I'm shooting underwater and its rarely possible to get any precise magnification data (its almost impossible to include a scale with skittish wild creatures) and because I'm shooting through a thick glass port any exif distance data will be wrong anyway (I'm using Canon so I don't think that distance data is recorded in any case).

[Charles Krebs]

its rarely possible to get any precise magnification data (its almost impossible to include a scale with skittish wild creatures)

This then is your biggest hurdle. Any software/photo measurement solution (highly sophisticated or very basic) will need some known reference in order to be "calibrated".

You may need to take a second shot away from the subject (without changing lens focus) of an object of known size.

If the lens offers a fine enough scale you might be able to record the focus distance (probably not really possible with today's lenses.) This would be better than nothing, but less accurate.

[rjlittlefield]

I'm wondering if there are any tools/plug-ins which will enable me to make 'relative' measurements in Photoshop? Sometimes these would be of curved details (such as fin rays) which I need to measure the size of relative to the fishes' total length or another defined size.

If I'm reading correctly, Paul does not need measurements on any absolute scale. What he writes sounds to me like the ratio of two arbitrary measurements made on the same subject. I am envisioning statements like ray length divided by total body length is between 0.1 and 0.15 .

In Photoshop, the basic Ruler Tool will provide straight line distances, but as far as I know you have to move them to some other tool to get the ratio. I am not familiar with how to use Paths as suggested by elf, but even if they can give the path length, there is still the issue of how to conveniently get the ratio.

I think what Paul is looking for is a tool that will directly report the ratio of two path lengths.

Paul, have I understood the problem correctly?

If so, does anybody know of such a tool?

--Rik

[Charles Krebs]

If that's the case Rik, then the inexpensive tool I mentioned ("Universal Desktop Ruler" http://avpsoft.com ) should work pretty nicely by simply taking two measurements.

[elf]

It turns out the length of the Path object is not shown directly in CS, but it is available from a script or plugin.

Here's a link to one such script: http://park12.wakwak.com/~shp/lc/et/en_ ... reasonably (you may have to scroll down a bit to see the Path Length script)

[Chris S.]

If I understand the need, PGK needs to measure both straight and potentially finely-curved lines relative to one another within an image of uknown scale. Universal Desktop Ruler would sort of allow this, by manually approximating the curve with a bunch of small straight line segments. But approximating a curve this way--likely on a repeated basis--seems tedious to me, and of limited resolution (resolution could be increase with the number of line segments, but tedium would scale right along with it).

I just tried a number of potentially easier approaches in Photoshop, using an open-source image of a goby fish. None of these approaches of mine worked. But each approach I tried used raster-based Photoshop features, and in a world of square pixels, measuring curves on square pixels seems likely to continue producing the kind of bad results I saw.

So I'd agree with a vector-based approach (such as the paths discussed already). But while Photoshop certainly has vector tools, its strengths are in raster-based editing--as evidenced by the need to add scripts or plugins to measure a path. Might it not be easier just to start with a vector-based program? I'd do this in Adobe Illustrator (a vector graphics editor) before I'd do it in Photoshop (a raster graphics editor with substantial vector graphics tools added), even though I'd walk at night through grizzly-bear country to avoid Illustrator.

On the other hand, this looks interesting--a program called "Inkscape":

http://wiki.inkscape.org/wiki/index.php ... nkscape.3F

It is a free, open-source vector graphics editor that does run on OSX (as well as other operating systems, but the the OP uses a Mac). I haven't tried it, because (though I don't like it much) I do know Illustrator enough to get by for what I do. But from what I see, Inkscape looks potentially good, and if I were trying to develop a quick, repeatable, accurate approach to what the OP needs, I'd give it a look.

--Chris

[Craig Gerard]

Paul,

I stumbled onto this application.....not sure if it is relevant to your requirements.

http://www.macnification.com/

Craig