How to callibrate scale bar?
How to callibrate scale bar?
I'm considering making the cross over from automontage to HF for my scientific illustration of insect specimens.
One necessity, however, is that I be able to obtain accurate scale bars relative to the magnification of the images. I'm shooting with a c-mount JVC digi cam running through a third ocular of a Lecia stereoscope with a zoom range of 7.11x-115x.
So, for example, if I'm zoomed in at 80x, I need a scale bar that accurately reflects that magnification, as opposed to if I were zoomed in at 75x or 82x or any other amount.
Anyone got ideas?
One necessity, however, is that I be able to obtain accurate scale bars relative to the magnification of the images. I'm shooting with a c-mount JVC digi cam running through a third ocular of a Lecia stereoscope with a zoom range of 7.11x-115x.
So, for example, if I'm zoomed in at 80x, I need a scale bar that accurately reflects that magnification, as opposed to if I were zoomed in at 75x or 82x or any other amount.
Anyone got ideas?
That seems like a major limitation compared to the calibration options available in software like Automontage. While it might not serve as an inconvenience for the artist, the scientist is generally required to show the scale of the illustration in any publication. I had been hoping to buy the pro version of HF as an alternative to Automontage, but without a simple scalebar callibration, it would be hard to justify.Ariel wrote: What you need to do is size the scale on-screen to match the actual subject. It's a manual job, no two ways about it.
Any creative work-arounds?
The only factor that should affect the length of the scalebar relative to the length of the subject is the magnification (zoom). The absolute size of the scalebar will vary according to printing, viewing, etc., but the size relative to the subject should always remain constant.Ariel wrote:Okay, depending on focus and lots of different elements (not to mention printing or viewing size), the scale will be different.
You're right. Printing doesn't matter here. However, no matter what zoom, objects farther from the camera will appear smaller than objects near the camera. Are you suggesting a feature which calculates the average DOF of the shots, coupled with camera and focal length, to automatically make a scale?ndemik wrote:The only factor that should affect the length of the scalebar relative to the length of the subject is the magnification (zoom). The absolute size of the scalebar will vary according to printing, viewing, etc., but the size relative to the subject should always remain constant.
I could see how that could theoretically work, but it wouldn't be accurate often enough, for the following reasons: A camera might not record the focus distance. A camera might incorrectly display the focus distance. Different cameras have different sized CCD sensors, focal lengths, and other specifications (meaning "5x zoom" on one camera with a 30-300mm lens would be significantly different from '5x zoom' on a camera with a 100-600mm lens), so it would only work with a list of specific cameras and, for SLRs, specified lenses. Using add-on lenses would also lead to incorrect results.
What you as a scientist have to do is measure the object you are working on yourself and then simply size the scale to match. Maybe the feature you are looking for can be added, but I'm not one to say. I think it is much more practical and reliable to do the measuring yourself. Or, you can do as many people do and include an actual measure in the photographs next to the subject. (You can even do just one photo with the measure and use this info to correctly scale one in the completed image.)
But seriously, I don't know if any programs exist which can do what you're looking for.
Thanks for helping me think about some of these issues. The program I use now, Automontage (Synchroscopy) allows for presetting as many calibration sets as needed. I've added a few screen shots to illustrate the feature.Ariel wrote: But seriously, I don't know if any programs exist which can do what you're looking for.
Basically, I image a micrometer at different zoom intervals, then use one of the program's measurement functions to measure a unit (i.e. 1mm). I then plug in the value of the measurement (i.e. 1mm) and the software calibrates the value to the magnification. So, if I'm zoomed in 45x, I select the preset calibration I made for that magnification, and the software gives me a calibrated scalebar.
I should also mention that I am working with a microscope zoom, not a camera zoom. The difference in focal length between the closest element of the subject and the farthest element is a matter of microns, and I don't think it significantly changes the scale.
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I see. That looks like a nice tool for micro photography where the user can pre-define microscope or zoom settings. I'll post a suggestion, maybe it will be added in the next version.
Comment on it here: http://forum.helicon.com.ua/viewtopic.php?p=3159#3159
Comment on it here: http://forum.helicon.com.ua/viewtopic.php?p=3159#3159
If the scale bar function in HF would accept some basic parameters such as sensor size, number of pixels/frame width, and magnification it could all be done automatically.
But here is a possible work-around.
ndemilk.... if you go to my site here:
http://krebsmicro.com/
you will see a link to a spreadsheet for scale bar calculations under "Articles and Resources". One reason I put this together was for determining scale bars using HF. Since HF uses either the # of pixels, or a percentage to create the scale bar size desired, that is what the spreadsheet provides.
Since I assume with your setup you normally use the same camera, the values for pixel width and sensor size will remain the same. The only variable in you case is the magnification. So while not completely "automatic" you can very easily see the value (in pixels or percentage) you need to produce the correct size scale bar. You could even modify the spreadsheet slightly and print up a chart (or create a file) that would cover the range of your magnifications.
BTW the latest Photoshop CS3 Extended offers some capability in placing calibrated scale bars (if that is ever an option in your case).
But here is a possible work-around.
ndemilk.... if you go to my site here:
http://krebsmicro.com/
you will see a link to a spreadsheet for scale bar calculations under "Articles and Resources". One reason I put this together was for determining scale bars using HF. Since HF uses either the # of pixels, or a percentage to create the scale bar size desired, that is what the spreadsheet provides.
Since I assume with your setup you normally use the same camera, the values for pixel width and sensor size will remain the same. The only variable in you case is the magnification. So while not completely "automatic" you can very easily see the value (in pixels or percentage) you need to produce the correct size scale bar. You could even modify the spreadsheet slightly and print up a chart (or create a file) that would cover the range of your magnifications.
BTW the latest Photoshop CS3 Extended offers some capability in placing calibrated scale bars (if that is ever an option in your case).
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Danylo,
I forgot to log in when I replied above. But I would like to add some additional thoughts.
While I appreciate the ability to place a scale bar in Helicon Focus, I too feel it would be much more useful if it were more "automated".
It is a simple calculation, and all that is needed from the user standpoint is the camera sensor size, the number of pixels on a side of the sensor, and the magnification at which the picture was taken.
Since for most users the camera sensor information remains the same, the program could save and display those values (of course they could be changed as needed). Then, all the user would need to input would be the magnification at which the picture was taken, and the desired size represented (ie: ".5mm", "100 micron") by the scale bar. The placed bar would then meet the users needs without the need for them to calculate values outside Helicon Focus.
For now, I think the spreadsheet I referred to above works well for those needing this info.
Charlie Krebs
I forgot to log in when I replied above. But I would like to add some additional thoughts.
While I appreciate the ability to place a scale bar in Helicon Focus, I too feel it would be much more useful if it were more "automated".
It is a simple calculation, and all that is needed from the user standpoint is the camera sensor size, the number of pixels on a side of the sensor, and the magnification at which the picture was taken.
Since for most users the camera sensor information remains the same, the program could save and display those values (of course they could be changed as needed). Then, all the user would need to input would be the magnification at which the picture was taken, and the desired size represented (ie: ".5mm", "100 micron") by the scale bar. The placed bar would then meet the users needs without the need for them to calculate values outside Helicon Focus.
For now, I think the spreadsheet I referred to above works well for those needing this info.
Charlie Krebs
Charles, thank you for pointing me towards your most illuminating website. Really brilliant work! I do think it will be possible to make a "cheat sheet" for plugging in accurately calibrated scale bars into HF.
If automating scale bar calibration seems feasible in the future development of HF, I can imagine it saving a nice chunk of time and transcription error in the long run.
If automating scale bar calibration seems feasible in the future development of HF, I can imagine it saving a nice chunk of time and transcription error in the long run.
Charles,
Thanks for your contribution to the discussion.
I personally do not trust formulas that includes several parameters. I think error of 10-15% is too high for me.
I think the best solution would be to calibrate the whole optical system in several points (x10,x50, x80) and then use the nearest calibration point if you need scale bar for some different magnification (x70). The program can calculate the scale bar by simple linear formula.
Thanks for your contribution to the discussion.
I personally do not trust formulas that includes several parameters. I think error of 10-15% is too high for me.
I think the best solution would be to calibrate the whole optical system in several points (x10,x50, x80) and then use the nearest calibration point if you need scale bar for some different magnification (x70). The program can calculate the scale bar by simple linear formula.