Christmas tree buds, using a ruler to provide scale

[Stanley]

I always like to see something included in the photograph to indicate scale. Here, I used a ruler. You can also print a scale on the image as well. Note that the bud in the foreground measures to be a bit less than 10 mm across its width.

Also observe the sap on the buds and stem.

[rjlittlefield]

Some indication of scale is good, especially for unfamiliar or surprising subjects. Rulers get the job done, albeit with some downsides that may or may not be important for any particular application. One of those is that a raw ruler tends to be visually intrusive no matter where it's placed. Another is that at higher magnifications, a ruler can be difficult to get into the same frame and the same focus plane as the subject.

What I usually do is shoot some sort of ruler as a separate image using the same optics, then use layering in post-processing to put in whatever length and style of scale bar seems best for the final image. If you search the forum archives for scale AND bar* , you'll find discussion of various alternatives. The method I use is described in the first half-dozen postings HERE.

Anyway, getting back to your image, because of the ruler and your comments about what to look at, I'm thinking this image is intended as a piece of technical documentation. This prompts some questions.

What kind of tree this is? Even though I don't recognize the exact species, these buds appear to my naive eye to be a typical size for the ones I do know. Is the size unusual or diagnostic in some way? Is the sap a normal condition, or does it indicate something unusual going on?

--Rik

[Stanley]

Hi Rik,

Thank you very much for your reply to my Christmas tree photo.

Actually, I don't mean this photo as technical documentation, because I am not a biologist of any kind. I just wanted to share a few macro shots that I have done over the years.

However, the issue of scale bars does interest me greatly. I know a bit about statistics, and I love to measure things.

Indeed, using rulers does get in the way of my photographs. There is the DOF issue, and my rulers set off horrible glare. I still have a number of photographs to post, and they often have rulers accompanied by these problems.

So, your explanation of what to do could be very useful. You say to "make a reference image by shooting a scale using the same optical setup as for your real subject."

The problem is that I do not have anything very sophisticated at all. Just a digital camera that I hand-hold close up. It is quite difficult for me to shoot even two consecutive photographs at exactly the same distance. Since we are shooting so close, then the movement of even one or several millimeters would render my hand scale bar inaccurate.

Wouldn't it? I would love to avoid having to use the ruler. But since I hand-hold it from one shot to the next, I don't see what else I can do.

Please advise, one and all.

Stanley

[rjlittlefield]

Are you using manual focus? If so, then just don't touch the focus control between shooting your subject and shooting your ruler. Instead, focus by moving the ruler. At macro scale, DOF is usually quite small compared to the distance from lens to subject. Making the ruler sharp will also make it be the same distance and thus the same scale as the subject.

If your camera has manual focus, but you're not using it, then I recommend to learn. There's definitely a place for auto focus in macro. I often use it in the field, especially for "arm's length macro" when lugging around a big backpack (like in this posting). But if you're working in a situation where you can stick a ruler next to your subject, then you're probably also in a good place to use manual focus.

Another trick that works even with auto focus is to take two pictures, one with the ruler and one without. The one with provides scale, which can then be added to the one without, in whatever form looks good. In this case the scale doesn't even need to be a ruler. Any object that can be measured after the fact will work fine, a coin for example. Once in a while you get lucky and even get to leave the scale object in the picture, as HERE.

Hope this is helpful. What sort of camera & lenses are you using?

--Rik

[Stanley]

Hi Rik,

I am using a Nikon Coolpix 4500. I know that that is definitely not cutting edge anymore, but it still works great. I enjoy the swivel on it.

I have never used the manual focus on it. I will check, but I don't think it is convenient to do on it.

Let me sort out what you are saying about using auto focus, in your last major paragraph.

Right, if I use manual focus then I would necessarily be at the same distance. Thus, as you point out, I would have the same scale, so that I could overlay the two images which would be on two layers using Photoshop Elements. I hadn't previously considered doing this, so that is a very useful idea.

However, if I use auto focus, then I may very well end up even slightly changing my distance. Then the scale would be different and I would not be able to overlay the two images, right?

The point is, I will see how easily I can switch over to using manual focus on my Nikon Coolpix. But if it is not convenient, I would like to continue using auto focus, but not have to continue to have the ruler in the same shot.

Thank you for your reply.

Stanley

[rjlittlefield]

However, if I use auto focus, then I may very well end up even slightly changing my distance. Then the scale would be different and I would not be able to overlay the two images, right?

True, at first blush. So what you do in that case is to use the subject itself to transfer measurements between images.

There are two ways to go, one graphical and one computational.

The graphical approach starts with overlaying the two images even though they don't have the same scale. Make one layer partially transparent. Then use whatever tool your image editor provides (in Photoshop it's Edit > Transform) to scale, rotate, and shift the image containing the ruler until the two images of the subject line up. The ruler goes along for the ride, and when the subjects line up, the ruler is then the proper size to construct a scale bar.

The computational approach starts with picking two easily identified features on the subject, as far apart as possible. Use the image that contains the ruler to measure the distance between those features. Then go to the picture that does not contain the ruler, and measure the distance in pixels between those same two features. Now you know the relationship between pixels and millimeters in the second picture, and you can use that to draw the scale bar.

I confess, I sometimes end up using one or the other of these techniques even when, in theory, I didn't need to. That's because I will often forget to do the overlay before I crop and resize the image. Then I find myself, for example, with a piece of a frame that has been resized down to 796 pixels, while my ruler is still sitting back in a full frame at 3072 pixels. Rather than repeat all the editing before the crop and resize, I'll just transfer the measurement from the full frame images of subject and ruler down to the cropped and resized frame, using one of the approaches described above.

--Rik

[Stanley]

Hi Rik,

But hold on.

The point is that one of my photographs has just the image of interest (let's say, a bug). The other photograph has only the ruler.

If one of my photos had both the bug and the ruler, then there would be no problem in my constructing a scale bar. Indeed, I could choose not to include a scale bar. Actually, I could simply use the photograph that had both bug and ruler, just as I have been doing.

What I need to get are two images (one with just the bug, and the other with just the ruler) -- and they need to have the same scale. Once I have achieved that, then I would be able to overlay the two photos and construct the scale bar. I could then choose either to show the ruler, or not show it, in my final photograph.

The issue is to get the two separate photos (one of the bug, and the other of the ruler) to have the same scale. There is my problem.

I appreciate your helping me with this matter.

Stanley

[rjlittlefield]

It may help to spell out my assumptions.

I assume the goal is to produce an image of the subject with an accurately sized scale bar that is placed, colored, etc. so as to detract minimally or not at all from the aesthetics of the subject.

If you can leave the optics unchanged between exposures, then this goal can be reached by shooting one picture of the subject alone and one picture of a ruler alone, using either limited DOF or measuring subject-to-lens distance so as to get the same scale for both pictures.

Under any other conditions, you have to shoot the subject and the ruler together in one image to determine scale. However, you can then transfer that scale onto an image of just the subject, using either of the methods I described and no doubt many others.

Notice that I'm focusing on the end result: how to get a picture of the subject with an accurate and attractive scale bar.

In some cases this can be done by combining subject-only and ruler-only images. In other cases the ruler-only picture is not adequate and one must use a subject-plus-ruler picture in its place.

You mention that you "could simply use the photograph that had both bug and ruler". But earlier you mentioned "my rulers set off horrible glare." That's one example of why the final image ends up better if you start with two pictures, one of them of the subject alone. There are a lot of other essentially aesthetic issues having to do with composition, colors, relative emphasis between subject and scale, and so on.

As an example, in the image that started this topic the ruler is bright, bold, and in the foreground. I may not be typical, but that ruler keeps yanking my eyes away from the buds and down to the tick marks and numbers. I suspect this is not really what you'd like to have happening.

By removing the ruler and inserting a much less obvious scale bar, you can keep the emphasis on the buds without losing the size information.

If you'd like, I can post a modified version of your image to illustrate what I'm talking about.

--Rik

[Stanley]

Hi Rik,

OK. Good answer. Now I understand what you are saying.

And yes, please by all means, post an edited photo of mine to illustrate your point. That would be useful.

Thanks again.

Stanley

[rjlittlefield]

Here are some variations on the theme.

10 mm bar, light:


5 mm bar, light:


5 mm bar, dark:


8 mm dimension lines, black:


For really busy images, sometimes you have to make a blurred-out space for a scale bar, like HERE. Sometimes I wrap up a scale bar with my signature, so there's only one blot on the image, like HERE. Or line 'em up, like HERE. Probably I'd reserve the black dimension lines for some case where that particular measurement was really significant. But there are no ironclad rules on these things; it comes down to a matter of personal taste and intentions.

For that matter the original image with the ruler works just fine for many purposes, and it's a lot quicker and easier to prepare. The archives at BugGuide.net have quite a few of them. I wish they had more, since many of their images don't have scale at all.

--Rik

[Stanley]

Hi Rik,

OK. Very nice and very instructive.

You've given me a goal to work for, to substitute my photos that already had or that will have rulers in them for scale bars. I will proceed to work on this technique.

You really have been very helpful, and I appreciate it.

Stanley

[waltknapp]

Indeed, using rulers does get in the way of my photographs. There is the DOF issue, and my rulers set off horrible glare.

On the business of glare and rulers the crime scene rulers are matte finish and come in several shades, at least the ones I found were like that. I keep a few of each shade in my kit. Here's a supplier:
http://www.lynnpeavey.com/index.php?cPa ... =3a&page=2

Walt

[Stanley]

Hi Walt,

Thank you very much. I have now looked at their site, and they have many measurement products that would be useful to me.

Stanley

[Stanley]

Hi Walt,

I have spent some time looking carefully at the website that you mentioned in your reply to my post.

I want to make sure that I order just what you have in mind. Many, many items are displayed (which is good, of course), but I am getting a bit overwhelmed as to what the best thing to purchase would be. Of course, if I could see firsthand what the products were, I imagine that I would be all set. But just from the photo, I am not quite sure.

It seems that the best thing for me is the following:

6" Vinyl Ruler 10-Count (05145, 05150, 05146, 05142, 09242, 05160, 05220)

The picture almost certainly shows a metric scale as well, which is all that interests me. I would get #09242, which is white, black, gray, and clear.

Is this the product that you mention keeping around?

Thanks.

Stanley

[waltknapp]

6" Vinyl Ruler 10-Count (05145, 05150, 05146, 05142, 09242, 05160, 05220)

It was a couple years ago I last ordered, but that appears to be the same as what I ordered. I also ordered one of their right angle rulers, but that's not seen much use. At the time I ordered a fair supply so it will be a long time, if ever before I need more.

Walt