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Photo Forum / Digital Photography / DSLR Cameras / April 2006Understanding resolution
First a little background. I was asked to take a group photo. I have a D70 and a couple of lenses, the one I used was my Nikkor 24-120 VR. In previous years, the photographer (no longer with us) used a medium format (Hasselblad, IIRC) and I knew I couldn't approach the resolution with my 6Mp. I set the camera to minimum ISO (200), aperture priority, f/16. VR was off, it was on a tripod. I shot the picture, EXIF tells me the lens was at 34mm, then I asked them to hold still a minute longer. I zoomed in a bit and shot a series of 9 photos -- left, middle, right starting at the bottom, then middle of the group, then the top -- with a couple of extra shots in there for good luck. The lens was at 70mm for these exposures. On the pixelboard I converted the RAW images, equalized the exposures as best I could, then set CS2 to work photomerging the shots. In the end, it took me about 6 hours to complete the merge to my satisfaction (if people would only hold still... LOL) OK, enough background. I compared the original single image to the merged shot. I COULD NOT BELIEVE THE DIFFERENCE. I knew the merged image would be sharper but this was incredible. I don't understand it, but I would like to, so if anyone has an explanation... The merged shots were at 2x the focal length which to me would be 4x the resolution. But the image looks MUCH sharper than that. Here's a low-res copy of the original single shot http://faczen.smugmug.com/gallery/452395/2/62072792 Here the same sized merged photo http://faczen.smugmug.com/gallery/452395/2/62071409 and here's a detail out of the two pictures for comparison http://faczen.smugmug.com/gallery/452395/2/62072791 Comments? Glenn Photo gallery at http://faczen.smugmug.com Reply via the web portal at www.faczen.com or email usenet at faczen dot ca > OK, enough background. I compared the original single image to the > merged shot. I COULD NOT BELIEVE THE DIFFERENCE. I knew the merged [quoted text clipped - 8 lines] > > Comments? Interesting, if you scale the detailed one to 25% then back up it's still better in some ways but worse in others. I think the bayer pattern and AA filter have a lot to do with the differences. >> OK, enough background. I compared the original single image to the >> merged shot. I COULD NOT BELIEVE THE DIFFERENCE. I knew the merged [quoted text clipped - 13 lines] > still better in some ways but worse in others. I think the bayer > pattern and AA filter have a lot to do with the differences. Think of it in terms of the number of pixel per face. Your single frame is like 3000 wide? Looks to me like maybe 30 faces edge-to-edge? A generous 100 pixels side-to-side in a face? You say the composite consists in three shots side-by-side; with overlap, at least twice the number of pixels per face, right? Or maybe I don't understand...  SignatureFrank ess >>> OK, enough background. I compared the original single image to the >>> merged shot. I COULD NOT BELIEVE THE DIFFERENCE. I knew the merged [quoted text clipped - 20 lines] > overlap, at least twice the number of pixels per face, right? Or maybe I > don't understand... I was thinking twice the width but my math was for 4x the width so that makes the experiment even more dramatic that it was still better in some respects. The difference between say 6MP & 12MP would be relatively minor though, only 75% of the width. 12mp = 4000 x 3000 6mp = 3000 x 2000 I use this technique a lot for my very large photo collages, where I just can't get enough resolution out of my 8MP. Firstly you may have put the zoom into a range where you get a sharper result, widest position is also often the softest. But the big gain is also just in pixels. Shooting a 3x3 grid, even with overlap, from a (rough) 3000 x 2000 to a 6000 x 4000, or 6MP to 24MP. Depending on how you did the overlap it might be even more. Cheers, Wayne Wayne J. Cosshall Publisher, The Digital ImageMaker, http://www.dimagemaker.com/ Blog and Podcast http://www.digitalimagemakerworld.com/ Personal art site http://www.artinyourface.com/ > I use this technique a lot for my very large photo collages, where I > just can't get enough resolution out of my 8MP. Firstly you may have [quoted text clipped - 3 lines] > 2000 to a 6000 x 4000, or 6MP to 24MP. Depending on how you did the > overlap it might be even more. I have a panoramic head that make taking the shoots much easier. It holds the camera sideways which gives allows you to get more sky then otherwise. I find that getting a good 40MP image is very easy and 100 to 200 MP is not too hard. Others have pushed this way up getting well over 1 Gpixel. The method works so well because the lens is only imaging a small part of the image at any one time. The result is that a cheap zoom lens can produce an image that is far sharper, when stitching photos, then the very best lens can produce in a single photo. The part I get a kick out of is that a fairly cheap camera can produce an image that is far better then a $40,000 state of the art digital camera. Of course there are limits to what you can photograph when stitching, but not as many as what most people believe. The other thing this gives us is sharp wide angle shoots, there are no wide angle lenses that are really sharp all the way to the corners of the image, but with stitching we can get very wide angle shots that are sharp all over. Scott Exactly. A panoramic head sure helps, but even a normal tripod at reasonable subject distances and handheld even with longer subject distances usually works very well. The thing with hand holding is to try to pivot around the camera rather than your body, just as a panoramic tripod head does. Even the best lenses have resolution limits defined by diffraction and some digitals get very close to this already. So it is a great technique. Scott, you should enter some of yours (perhaps cropped) in the panorama competition running on my main site. Cheers, Wayne Wayne J. Cosshall Publisher, The Digital ImageMaker, http://www.dimagemaker.com/ Blog and Podcast http://www.digitalimagemakerworld.com/ Personal art site http://www.artinyourface.com/ > Exactly. A panoramic head sure helps, but even a normal tripod at > reasonable subject distances and handheld even with longer subject [quoted text clipped - 15 lines] > Blog and Podcast http://www.digitalimagemakerworld.com/ > Personal art site http://www.artinyourface.com/ Even with a P&S camera you can get good results like this. http://www.shuttertalk.com/forums/images/upload/Pano-1--smaller.jpg > Even with a P&S camera you can get good results like this. > > http://www.shuttertalk.com/forums/images/upload/Pano-1--smaller.jpg Yes indeed, I think the main two things that help for high resolution photos is a somewhat long lens and being able to set the shutter and aperture to fix setting. I find it interesting that under the right conditions a $20 lens can out perform a $2000 lens. Scott > First a little background. I was asked to take a group photo. I have a > D70 and a couple of lenses, the one I used was my Nikkor 24-120 VR. In [quoted text clipped - 9 lines] > extra shots in there for good luck. The lens was at 70mm for these > exposures. Well a 4X increase in the number of pixels is a pretty big gain, but added to that is the fact that zoom lenses at their wide angle point are much softer then at a more normal FL. Scott >First a little background. I was asked to take a group photo. I have a >D70 and a couple of lenses, the one I used was my Nikkor 24-120 VR. In [quoted text clipped - 38 lines] >Reply via the web portal at www.faczen.com >or email usenet at faczen dot ca You are experiencing something called "passing a detail threshold." If you take an image at 2x the magnification of another image, you will end up by seeing details 2x smaller than what you could with the image with lower magnification. However, if the image you are taking has numerous details that suddenly appear at a specific magnification, the image will appear even sharper than you thought it might. Had you taken a shot of something else, it might not appear so much more detailed. It all depends on the subject. |
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