# Take pictures at real-world size without a 1:1 lens



## Bedo (Oct 31, 2012)

For a university project I need to take photos in scale 1:1: in the computer screen they must have the same size that they have in the real word.

I have a D7000 with these lenses: 18-105mm, 50mm 1.4, 55-300mm, no macro lenses 1:1.

How can I set up my environment to obtain this result? How can I calculate the distance from the subject? Or how can I scale the final photo?


I hope there is a better solution than placing a ruler near the subject, because I have to shot and convert a lot of photos... :mrgreen:

Thank you


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## Tiberius47 (Oct 31, 2012)

Do you mean the image on the screen has to be the same size as the actual object?  If that's the case, then no problem, it's easy.

But if you mean that the image on the camera's sensor needs to be the same size as the actual object, then you're going to need a macro lens or extension tubes or something like that.


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## The_Traveler (Oct 31, 2012)

What are you taking pictures of?


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## Dao (Oct 31, 2012)

The_Traveler said:


> What are you taking pictures of?


I hope it is not an elephant.


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## jake337 (Oct 31, 2012)

Tiberius47 said:


> Do you mean the image on the screen has to be the same size as the actual object?  If that's the case, then no problem, it's easy.
> 
> But if you mean that the image on the camera's sensor needs to be the same size as the actual object, then you're going to need a macro lens or extension tubes or something like that.





Dao said:


> The_Traveler said:
> 
> 
> > What are you taking pictures of?
> ...



You will need a macro lens which will focus to 1:1 or a larger sensor film aka medium, large format or larger.

If it is an elephant you'll need something like or larger to shoot at 1:1...

MAKE | A Camera Large Enough to Live In


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## tirediron (Oct 31, 2012)

It will take a little trial and error to get exactly 1:1, but the most economical solution is a reversing ring.


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## Dao (Oct 31, 2012)

But I think we still do not know what OP really need.

Is the assignment require to display an object on the screen in 1:1 ratio or the image need to be recorded at 1:1 ratio.

I can take a photo of my mobile phone and then display it on my computer screen and adjust it so that it is same size when I put my real phone next to the image on the screen.

Of course, when I display the same image on my TV, the image is going to be bigger than my phone.


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## unpopular (Oct 31, 2012)

You are not going to be able to reproduce the same size on every screen without programming.

On any given screen, you can reproduce at 1:1 by factoring in the screen pitch, the screen size and the size of the image. For example, if you have a 16:9, 15" screen with a display resolution of 1440x900, the dot pitch in dpi would be around 110 dpi. This means that at 100% enlargement, every inch will be equal to 110 image pixels. A five inch subject in any dimension would thus be 110p x 5" = 550p. However, if I set the resolution of the monitor lower, then the each _image_ pixel will represent more physical space, higher each _image_ pixel will represent less. So if you're trying to get 1:1 reproduction on the web, for example, it's not going to be possible without first knowing the monitor's dot pitch.

The most reliable way to reproduce on one screen actual size is to photograph a ruler, and resize at 100% viewing size until the ruler in the image lines up with a real ruler held up to the screen. Provided that the photograph the the ruler and the photograph of the subject start out with the same magnification and file size, you can resize the subject by the same factor as you had the ruler.

For absolute assurance, photograph a ruler with the subject for scale, and crop out the ruler.


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## 480sparky (Oct 31, 2012)

1:1 means the image projected onto the film plane or digital sensor is the same size as the subject is in real life.  An optical method to achieve this 1:1 ratio can be a macro lens, close-up lenses, reversing ring, extension tubes or bellows.  There's no magic way of creating a 1:1 ratio without the gear to do so.

Your D7000 sensor measures 23.6mm x 15.6mm.  This means a subject that is 23.6mm x 15.6mm in size will fill the frame when a 1:1 system is used.  Cropping a 1:2 image in post is not the same.  It would still be 1:2.  By the same analogy, you can't shoot with your 300mm lens, crop it in post, and say, "I shot this with a 500mm!"

Not sure what you mean by 'converting' photos.


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## unpopular (Oct 31, 2012)

^^ I think OP means reproduction size, not magnification. For this, you wouldn't need a macro.


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## 480sparky (Oct 31, 2012)

unpopular said:


> ^^ I think OP means reproduction size, not magnification. For this, you wouldn't need a macro.



Reproduction size IS magnification.  1:1 repro is the same as 1x mag.


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## unpopular (Oct 31, 2012)

The two terms are erroneously used interchangeably, and likely this arises from large format when contact printing was common.


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## The_Traveler (Oct 31, 2012)

I think that the OP is not clear about what he/she wants to do.
Posing solutions to ambiguous questions is a waste of time.


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## unpopular (Oct 31, 2012)

With all fairness, I think some of the ambiguity comes from the terminology issue I mentioned above.


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## Mully (Oct 31, 2012)

The OP is saying it must be the same size as in real world, not too difficult.


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## TCampbell (Oct 31, 2012)

You may want to clarify the instructions with your instructor.  Normally, when we discuss "1:1" image scale in photography, we're talking about the size of the object on the CAMERA SENSOR and not the object size on the computer screen.  That's a huge difference.

Let's just assume your instructions were correct and your instructor did mean the computer screen (which would be odd, but we'll go with this idea for now.)  The resolution accepted for monitors is generally 72 dpi (dots per inch).  HOWEVER... most modern monitors have surpassed that by quite a bit.  My own monitor is doing just slightly over 100 dpi.  You'd need to use an editing program (e.g. photoshop) to resize the photo based on this.  For example... suppose you snapped a product photo of your mobile phone.  Let's suppose the mobile phone is 5" tall.  Based on a 100 dpi monitor resolution (or whatever dpi you're working with) you'd resize the image so that the area phone itself occupies 500 lines from top to bottom (not the full image size... just the phone.  So if the full image had an extra 1" margin above and below the phone you'd need to account for that.)

HOWEVER... I suspect you mis-heard your instructor and when he/she asks you to get an image at "1:1" scale, he/she is really talking about macro photography.  In macro photography, the image size on the CAMERA SENSOR is the same size as the object in real life.  

Let's use a &#8364;0.01 coin as an example:

The coin has a diameter which measures 16.3mm.  Your Nikon D7000 has an APS-C size sensor which measures 23.6mm x 15.6mm.

That means that if you were to take a photo of this coin at 1:1 scale, the count would fit horizontally (with room to spare) but it wouldn't actually fit in the image vertically... the coin is .7mm larger than the height of the sensor -- so you'd slightly clip off the top & bottom of the coin.

After taking such a photo, when you display it on the computer screen, the coin will be huge!

There are numerous ways to take close-up photos.  The highest quality method is to use a true 1:1 scale macro lens (be careful, because lots of lenses advertised as "macro" can't really do 1:1 scale... generally if it's a "zoom" lens that also claims to be a "macro" lens then it's not really a 1:1 scale lens.  But usually the prime (non-zoom) lenses that claim to be "macro" are 1:1 scale (I do know of a few exceptions so you still have to be careful.)

You can buy close-up diopters.  These are generally single-element lenses that thread onto the end of the camera lens.  While they do let you get closer, the single-element design has drawbacks.  If you've ever used a simple magnifying glass to look at the text on the pages of a book, you might notice that the center is magnified, but the edges show color fringing around the edges of the letters (even though the print is supposed to be black print on a white page.)  The color "fringing" is caused by the dispersion (chromatic aberration) of the edges of the lens behaving like a prism and splitting light into it's constituent wavelengths.  Close-up diopters are generally very inexpensive.

You can use "extension tubes".  These are simple hollow barrels.  You attach the extension tube to the camera body, then attach the lens to the other end of the extension tube.  By moving the entire lens farther from the camera you are effectively reducing the closest focusing distance allowed by the lens and creating a larger image (actually they reduce the entire focusing range -- the lens will generally not be able to focus out to "infinity" when attached to an extension tube).  There is no glass or lens element of any kind in an extension tube -- they are completely hollow (nothing but air inside).  Since there are no lenses, there's no degradation of optical quality (well... that's not entirely true... lenses are technically optimized for a specific back-focus distance.)  Let's just say the degradation would be minimal -- especially when compared to "close-up" diopters.  Extension tubes also tend to be very inexpensive because of their simplicity (they usually do have electronic contacts so that they do pass the camera's communication pins through to the lens.)

You can also use a "reversing ring".  This simple little gadget is a ring that has the camera's bayonet style mount on one side of the ring, and camera lens "filter" threads on the other side.  So screw it on to the FRONT side of your lens (as though you were attaching a filter.)  You now have a bayonet mount on the FRONT of your lens.  Turn the lens around and connect it to your camera body.  The downside is that since the lens is mounted backwards, you have no control over it.  You manually focus it.  You can't control the f-stop.  

Back up at the top, I mentioned using a true "1:1" macro lens.  With that option there are no compromises.  You have full control of everything.  The auto-focus works.  The f-stop works.  You don't have optical compromises.  You get to use the full focal range of the lens.  BUT... while this is certainly the most fully-functional / least compromises path, it's also the most expensive.

If you were really doing macro work seriously, then get the true macro lens.  For a class project, use one of the other methods (especially since students are supposed to be poor & starving and not enough money to buy gear.)


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## Bedo (Oct 31, 2012)

Thanks for all the replies. 

First of all I apologize because I didn't write the question very well. 

I actually don't need to take photos in 1:1 scale (in the sense that my image shouldn't be at real size on the CMOS sensor).



What I really need is to use the well-know relation:


1 pixel = 0.264583333 millimeters 


So if I place a 100mm ruler on the photo, it must be saved with ( 100 / 0.264583333 ) pixels on length.


How can I obtain this result?


By the way I need to take pictures of human-ear in order to perform a psychoacoustic experiment.


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## unpopular (Oct 31, 2012)

If the exercise is not about pixel relationship to physical space, then I'd just use a scale.

I had a project that required 1:1 reproduction. I quickly learned that using a physical scale is really the only way to go. I had all sorts of complicated means of doing this, but in the end it just wasn't reliable. There are so many factors involved with magnification, it's much easier just to photograph a ruler or some other known size in the scene and use it as a reference.

This is why when you see scientific and forensic photographs there is often a ruler or square in the frame.


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## Helen B (Oct 31, 2012)

Assuming that you mean what you say - ie 1:1 on your computer screen - it is quite easy to set up to do repeatedly and quickly. First display any photo you have taken with the D7100 on your screen in the exact way you intend to show the future images. Then try to take a focused picture of that picture, filling the whole frame, or if the aspect ratio doesn't match, one side of the frame. Try all your lenses. It doesn't matter if you can't get an exact match - just select the picture that gets closest. Note the distance from lens to screen, and make yourself a little rig to hold the camera that distance from the object. It can be a piece of string, a short chain, a simple wire frame - use your ingenuity.

Now, whatever standard process you use to resize the newly taken image so that it fits the original screen image (ie the new screen image is identical to the original screen you took the picture of) can be applied to the pictures you take using your rig. 

This is a minor adaptation of old, proven techniques used to churn out images at an exact, repeatable magnification without having to do individual measurements or calculations. I've been brief, so ask if anything is unclear. The principles are really simple.

Edit: You wrote your clarification while I was typing that. The above will work for you, with a slight modification to account for any difference between the screen you use for the original test and your 'standard' pixel pitch.

You might want to get a simple diopter. It sounds like you won't need much more, if anything.


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## amolitor (Oct 31, 2012)

Yes Mully. But what is 'it'?


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## 480sparky (Oct 31, 2012)

amolitor said:


> Yes Mully. But what is 'it'?


...............


Bedo said:


> ........By the way I need to take pictures of human-ear.............


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## The_Traveler (Nov 1, 2012)

Bedo said:


> First of all I apologize because I didn't write the question very well.
> I actually don't need to take photos in 1:1 scale (in the sense that my image shouldn't be at real size on the CMOS sensor).
> *What I really need is to use the well-know relation:
> 
> ...



This is all proving quite illuminating to me.
I can't, however, concede that a single pixel is .264 etc mm. 
If that were so than a D800 sensor would be several times larger than a D700 sensor but we know that the physical dimensions are very close to the same.
My D700 sensor is  36 mm and 4000 pixels long, thus a single pixel is .008456.

If you save something so that the dimensions in pixels is the same size as the object in millimeters that would mean that a 100 mm ruler (approximately 4 inches) would 
look like this 

but the actual display in size on your screen would be dependent on the screen size and resolution.
Thus a human ear (about 70 mm) would be 
  but also dependent on screen size and resolution.

Instead of trying to put this in terms of resolution, why not just tell us what you are trying to accomplish and that will give us a better hint of how to respond.


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## Bedo (Nov 1, 2012)

We are using this conversion value: Meter Pixel Conversion -- EndMemo



> Instead of trying to put this in terms of resolution, why not just tell us what you are trying to accomplish and that will give us a better hint of how to respond.



We need to calculate the time that the sound needs to go from the external pinna to the ear focus point. We calculate it as distance / sound_speed.

So we need to calculate the exact ear size (width, height, ... ) starting from a photo.

We could place a ruler but we need to take a lot of photos so I would like to know if there is a way to calculate the correct focal lenght and subject distance with a particular lens to obtain a conversion value of 1 pixel = 0.264583333 millimeters


By the way I'm also curious to understand how the relation 1 pixel = 0.264583333 millimeters has been calculated. I searched for it on Google but I didn't find an answer...


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## unpopular (Nov 1, 2012)

Bedo said:


> We are using this conversion value: Meter Pixel Conversion -- EndMemo



I am not sure what to make of this calculator, but I am pretty sure it's not doing what you think it is.


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## Bedo (Nov 1, 2012)

Yes, I would really like to know how the conversion 1 pixel = 0.264583333 millimeters has been calculated.

I'm going to ask to [FONT=Helvetica, Tahoma, Arial, sans-serif]my postdoctoral student and let you know![/FONT]


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## Helen B (Nov 1, 2012)

The standard method I already suggested will work for you. Now that you have explained more (why didn't you do that to begin with?) it is even simpler. You make a wire frame that holds the camera (with pre-focused lens) a fixed distance from the ear. First you use it to take a picture of a ruler. This tells you your real pixel dimension to use for later image pixel-distance conversion (ie _your_ pixel to mm conversion). (Forget that equivalence you found somewhere - it isn't appropriate for you and you are simply confusing yourself with it.) Then you take pictures of the ears, framing them in the wires. Use the longest lens you have to limit errors caused by distance. This is all tried and tested practice.


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## amolitor (Nov 1, 2012)

The pixel size of 0.264mm is, I think, a pretty standard dot pitch for monitors at some standard resolutions. I assume from this that the OP is interested in rendering things in "real life" size on a monitor.


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## Helen B (Nov 1, 2012)

amolitor said:


> The pixel size of 0.264mm is, I think, a pretty standard dot pitch for monitors at some standard resolutions. I assume from this that the OP is interested in rendering things in "real life" size on a monitor.



That's what I thought the first post sounded like (1:1 on the monitor). Now it sounds like all that is required is a simple way of quickly converting from image pixels to distance. The 0.26 mm thing is a red herring, and the sooner the OP realizes that the better. The quoted 9 sf precision is kinda worrying, however. Also strange is the absence of a response to the various methods already suggested.


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## amolitor (Nov 1, 2012)

Helen B said:


> amolitor said:
> 
> 
> > The pixel size of 0.264mm is, I think, a pretty standard dot pitch for monitors at some standard resolutions. I assume from this that the OP is interested in rendering things in "real life" size on a monitor.
> ...



Yes, to all of this


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## The_Traveler (Nov 1, 2012)

Helen B said:


> The standard method I already suggested will work for you. Now that you have explained more (why didn't you do that to begin with?) it is even simpler. You make a wire frame that holds the camera (with pre-focused lens) a fixed distance from the ear. First you use it to take a picture of a ruler. This tells you your real pixel dimension to use for later image pixel-distance conversion (ie _your_ pixel to mm conversion). (Forget that equivalence you found somewhere - it isn't appropriate for you and you are simply confusing yourself with it.) Then you take pictures of the ears, framing them in the wires. Use the longest lens you have to limit errors caused by distance. This is all tried and tested practice.



What Helen said is totally right on the money.
I have done this exact thing (with teeth rather than ears)

Fix the camera to object distance (preferably as close as possible to filling the frame but at some distance to minimize placement error but maximize size, so using a 105 macro or a macro adaptor on available lens )
Take a picture of a high accuracy rule that is on the same plane as the subject.
ABFO No. 2 Photomacrographic Scale - Arrowhead Forensics   or  Motion Control Systems and Components
Working at known size of viewed image, measure with the PS built-in ruler (record x and y values) and record

(Ideally you could place the ruler over the ear and take a image of the rule with each subject.  That would maximize accuracy and minimize effects of subject distance error, etc. but require extra measurements. This could be an advantage by writing the subject number on the rule and thus identifying each image.)

Record x and y distance so that rotation and displacement problems are minimized. Then calculate hypotenuse to get real distance and normalize using the original measurements of the ruler.

All of the calculations can be done just by entering the x and y values in a spreadsheet and using formulae to calculate it all easily.


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## Bedo (Nov 1, 2012)

Helen B said:


> The standard method I already suggested will work for you. Now that you have explained more (why didn't you do that to begin with?) it is even simpler. You make a wire frame that holds the camera (with pre-focused lens) a fixed distance from the ear. First you use it to take a picture of a ruler. This tells you your real pixel dimension to use for later image pixel-distance conversion (ie _your_ pixel to mm conversion). (Forget that equivalence you found somewhere - it isn't appropriate for you and you are simply confusing yourself with it.) Then you take pictures of the ears, framing them in the wires. Use the longest lens you have to limit errors caused by distance. This is all tried and tested practice.



Yes I think that I will try this approach! Thank you



amolitor said:


> The pixel size of 0.264mm is, I think, a pretty standard dot pitch for monitors at some standard resolutions. I assume from this that the OP is interested in rendering things in "real life" size on a monitor.



Maybe it is a pretty standard for 72ppi monitor but I tried to calculate it and obtain the same result, without any luck... Are you able to obtain this *magic dangerous value*? It is interesting...



Helen B said:


> amolitor said:
> 
> 
> > The pixel size of 0.264mm is, I think, a pretty standard dot pitch for monitors at some standard resolutions. I assume from this that the OP is interested in rendering things in "real life" size on a monitor.
> ...



I insisted on the 0.264mm because it has actually been used on a IEEE scientific publication, so I will definitely investigate about this.

Thank you a lot for the help  I'm going to try/ask something and then let you know


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## unpopular (Nov 1, 2012)

^ as I said, I'm sure 0.264mm/p is *something* I'm just not sure it's what you need.


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## The_Traveler (Nov 1, 2012)

Here is an excellent procedural article on how to do anatomic measurements and correct for distortion in placement but it requires the ABFO-2 ruler. 
Roger D Metcalf DDS JD D-ABFO - Bitemark Photography Tips 1


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## unpopular (Nov 1, 2012)

^^ which is cheap.

http://www.crimescene.com/store/index.php?main_page=product_info&products_id=342

I really think that's the best approach. since this is dealing with scientific imaging there's no aesthetic reason not to just use a scale.


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## enzodm (Nov 4, 2012)

Bedo said:


> I insisted on the 0.264mm because it has actually been used on a IEEE scientific publication, so I will definitely investigate about this.
> 
> Thank you a lot for the help  I'm going to try/ask something and then let you know



if you found that value in a scientific paper, it is because in their case this was their value -it's not like pi. If you have to show on your computer, you have to calculate your value (and however maybe will not be valid on your teacher computer). Measure the size of your monitor (e.g., on horizontal - pixels are not exactly squared, but for your needs you can approximate), divide for the number of pixels you are using (e.g., 1280), and that's all.

For the "difficult" part, Helen's method is the right way. If your exercise allows it, you might even apply a known marker close to the ear (e.g. an adhesive circle of known size). You may eve use ImageJ to calibrate the image size (Analyze/Set scale).


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## EchoingWhisper (Nov 4, 2012)

What screen can fully show the elephant in life size a meter away?


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## unpopular (Nov 4, 2012)

EchoingWhisper said:


> What screen can fully show the elephant in life size a meter away?



this screen should work.


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## The_Traveler (Nov 4, 2012)

If I had to do a great many of these I would buy an additional metal lens hood and create a wife frame attached to that with a plexiglass with cutout for ear and the scale above cemented in place.
Lift the camera, place cutout over ear and shoot.
We used things like this for clinical stuff but I can't find an illustration of it.


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## enzodm (Nov 4, 2012)

The ruler is needed in each picture only if something changes in the geometry (distance or focal length). If not, you may calibrate once. On the other side, if there is a ruler, there is no need for the wireframe thing, aimed at maintaining geometry.


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## The_Traveler (Nov 4, 2012)

enzodm said:


> The ruler is needed in each picture only if something changes in the geometry (distance or focal length). If not, you may calibrate once. On the other side, if there is a ruler, there is no need for the wireframe thing, aimed at maintaining geometry.



I have found that the advantage of having a ruler (we didn't use abfo-2 because it wasn't yet available, just used a segment of plastic mm. rule) in every shot is that every individual shot, if necessary, can be verified as to geometry.  

Our typical process was to pick a few samples at random, verify that the lens-subject distance was the same (we were using fixed focal length lenses on much more primitive cameras) and we were confident that the situation was stable.  The plexiglass surround also was a convenient place to put a piece of tape with the subject number. Thus each slide (film) was self-verified and self-identified with no worries.


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## Buckster (Nov 4, 2012)

This conversation has all been very interesting to me.  I don't know that I have anything to really contribute here, but I thought I'd run an experiment on my own here to see what happens.

First, I used Photoshop to view the final image and, importantly, I used a view of "Print Size" for accuracy.

To prepare for that, I'll note that my monitor size is calibrated in Photoshop so that when I'm viewing something in "Print Size", 1" = 1" and can be confirmed on the Photoshop ruler.  For those who don't know how to achieve that, it's pretty simple: Measure the physical screen area of your monitor.  In my case, that's 23.5" wide by 13.25" tall.  My screen resolution is 1920 X 1080.  1920 divided by 23.5 inches means that I have 81.7 pixels per inch on the horizontal measurement.  1080 divided by 13.25 means that I have 81.5 pixels per inch on the vertical measurement.  In Photoshop, go to Edit > Preferences > Units & Rulers > Screen Resolution and plug in 81.5 (in my case).  That completes the "Print Size" calibration in Photoshop.

Next, I took a photo of my ear with a ruler just below it, then brought it into Photoshop.

I straightened it using the edge of the ruler, then zoomed in and cropped it precisely at the inch markers that would include the whole ear.  That made the image 3" wide, per the ruler visible in the shot.

So I resized the canvas to precisely 3" wide to properly size it.

Then I viewed it in "Print Size".  When I held my real-world ruler up to the screen, sure enough, it matched the Photoshop ruler and the ruler in the photo - precisely 3" wide; The photo of my ear on the screen at that moment was 1:1 - "actual size".

Then, just for giggles, I printed it.  Placing my ruler beneath the ruler in the print, they matched, 1:1 - both were 3" wide.  The print of my ear was "actual size".

Don't know if that's at all useful, but it was both fun and enlightening on this end.  :thumbup:

Here's the cropped picture of my ear that I used for the experiment:






Note that it won't be 1:1 on your screen unless your screen really IS 96 ppi, which is what the image was saved at for web viewing, AND your browser is displaying at 100% size.


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## Bedo (Nov 10, 2012)

Buckster said:


> This conversation has all been very interesting to me.  I don't know that I have anything to really contribute here, but I thought I'd run an experiment on my own here to see what happens.
> 
> First, I used Photoshop to view the final image and, importantly, I used a view of "Print Size" for accuracy.
> 
> ...



This is really interesting! Thank you a lot!

I've just measured my screen size and it looks like I have 93ppi. My measure is quite accurate

However some software (e.g. Matlab) reported that I have 96ppi! And Photoshop should display the ruler correctly when I set it at 96ppi, not 93ppi! I think I'll use 96ppi.

By the way I discovered that "magic conversion factor":

pixel to meters: 1/96 * 2.54 / 100 = 0,0002645

But this doesn't work in general.

See: matlab - convert pixel to cm - Stack Overflow


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## Bedo (Nov 10, 2012)

Helen B said:


> The standard method I already suggested will work for you. Now that you have explained more (why didn't you do that to begin with?) it is even simpler. You make a wire frame that holds the camera (with pre-focused lens) a fixed distance from the ear. First you use it to take a picture of a ruler. This tells you your real pixel dimension to use for later image pixel-distance conversion (ie _your_ pixel to mm conversion). (Forget that equivalence you found somewhere - it isn't appropriate for you and you are simply confusing yourself with it.) Then you take pictures of the ears, framing them in the wires. Use the longest lens you have to limit errors caused by distance. This is all tried and tested practice.



I think we will use this method!


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