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Old Jun 16, 2004, 9:09 PM   #1
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What about this logic?

If I use a 2 megapixel camera to take 2 photo's then join them together with the CanonPhoto Stitch program doesn't that equal what ones gets from a 4 megapixel camera with the same optics? (if we ignore the loss in the overlap)

If this logic is correct then a good zoom is even more useful as one could zoom up on an object, take several pics that are stitched together and the result is a high resolution picture from a cheapish camera.
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Old Jun 16, 2004, 11:44 PM   #2
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well....the stitching isn't very easy...and unless the subject and you stay completely still (your camera has to stay at the exact height it's at for all the shots...and it can't move side to side...) a tripod is necesary...

but i'm pretty sure the logic is correct....2x2=4
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Old Jun 17, 2004, 8:02 AM   #3
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The only problem with that logic is that a picture is a two-dimensional object. By joining two images side by side you only increase the resolution in one dimension. You would need two more images to increase the height also. You would need to stitch four images together to match the resolution of a 4MP image. It may be easier just to buy a 4MP camera.
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Old Jun 17, 2004, 8:53 AM   #4
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If you could stitch them with no overlap you would get 4Mp from two 2Mp shots. I often take two shots with the camera held vertically to get a 28mm shot from a 38mm lens. The resulting image is about 8.5Mp from a 5Mp camera because of the overlap.
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Old Jun 17, 2004, 10:19 AM   #5
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Combining 2 pictures does not change the original resolution of either picture. It creates a larger picture with the same resolution (pixels per inch).
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Old Jun 22, 2004, 11:06 AM   #6
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With regard to tod651's comment, I think pixels per inch is a term that really only applies to printing a picture, and then it depends on what size print you are making. By stitiching pictures together you do get more pixels in the image. I think you have to consider other factors, like zoom level. Two 2MP pics, taken vertically and stitched together, would make about a 3 or 4 MP pic, with allowances for overlap and maybe a little different height to width ratio. You could take a similar picture with a 3 or 4 MP cam if you were at a wider angle zoom, since you would have had to zoom in to get about half of the image in the frame with the 2MP cam, whereas you want the entire image in the frame of the 3 or 4MP cam. So the number of pixels defining each particular feature or detail in the picture would end up similar, which is what resolution really is.

I've read stories about pics made by stitching together hundreds of highly zoomed shots to geta final result inthe hundreds of MP range. You could take the same shot at a much lower resolution with one click by using a wide angle zoom. Pixels per inch has no bearing on this issue until you try to print an image - more pixels = bigger possible prints.

Of course, as noted, there are downsides to just assuming you can easily come up with high resolution pics this way. Movement in the frame, clouds coming in to give different exposures on each shot, water ripples not matching up, cloud shadows not matching up, and so on.

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Old Jun 22, 2004, 2:18 PM   #7
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Technically, you would have about 4 million pixels, but the picture is also twice as big, so you still have 2MP quality, just bigger.
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Old Jun 22, 2004, 4:06 PM   #8
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Quality- dpi? An image stored in the camera is a group of pixels - no such thing as dpi in camera, no difference in "quality"- just more pixes when theres 4 million of them than when there's 2 million of them. Pixels is pixels until you go to print.

1st picture: 2,048 x 1,536 pixels (3,145,728 total pixels) or 3.14 Mega (million) pixels

Put 2 pictures next to each other (for simplicity assume no overlap) and stitch them together and the new image size is:

4096 x 1536 pixels or (6,291,456 total pixels) or 6.29 mp

Unfortunately you need 2 more pictures to stack on top of these 2 to print normal print size. So - 2 more on top stitched together and your final stiched picture is 4096 x 3072 or (12,582,912 total pixels) or 12.58 mp.

To campare- printed at 4x6":

A 4mp camera: 2272 x1704 pixels - has to be cropped (since the camera takes at a 3/4 and we're printing at 4/6): Total Pixels 2272 x 1515. Translates to 379 dpi when printed (dpi only uses one coordinate measurement as opposed to sensor pixels which is total pixels or x times y).

Now our stitched together photo from our 3mp camera ended up 4096 x 3072 - crops to 4096 x 2731 to reach the correct aspect ratio and prints at 683 dpi when printed 4x6". (of course your printer maxes out eventually and most places are happy with 300 dpi.)

In jpegs the dpi setting is a text tag and very nearly meaningless (I don't know a printer anymore that reads that as the final resolution to print at- they usually just look at your order and print as high as dpi as they can with what pixels they're given up to the limit of the printing device.)

Hope this isn't as confusing as it looks.


edited: math error.
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Old Jun 22, 2004, 7:24 PM   #9
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Quote:
Unfortunately you need 2 more pictures to stack on top of these 2 to print normal print size. So - 2 more on top stitched together and your final stiched picture is 4096 x 3072 or (12,582,912 total pixels) or 12.58 mp.
Actually you don't if you hold the camera vertically. This is a stitch of 2 5Mp images. The result is about 8.5 and it takes my 38mm to about 28mm.


You and ir are correct that PPI is immaterial in an image until you size it for printing or display. If you stitch two 2Mp images together to get a 3.5Mp image it is the same size as any other 3.5Mp image and will give the same resolution for a given print or display size.
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Old Jun 23, 2004, 11:23 AM   #10
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I think there is a subjective factor at work here.

Pixels per inch is a valid concern even in the camera. The CCD that senses the light through the lens and creates the stored image in the camera produces a given quality for the number if pixels it contains - 5m cameras produce a higher resolution (more PPI) image than a 2m camera can.

For any given picture size, quality is resolution is PPI, whether in the camera, on a screen or on a printer.


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