Contact print versus digital (aerial stereophotos)

<p>Hi All,<br>

<br />Previously, our municipality has always had contact prints done of our aerial photos (9" x 9"). And the detail on the print was phenomenal. When seen through a microscope, the print was clearly better than the high end prints I usually get from our best photofinisher in town. <br>

But this year, the contractor flew with a digital camera. The file had incredible detail (even more than what we obtained from high end scans of the film from years before. But the resulting prints were terrible. (I've attached a combination 1,200 dpi scan of the two prints on either end, sandwiching the screen capture of the digital). <br>

<br />So I'm wondering if the image on the right is the best quality that's possible. I have my doubts. <br>

Thanks in advance.</p><div></div>

There is no reason a print cannot be made that demostrates the detail available in the digital image it is made from.

 

If I read what you write correctly, the right hand image was produced from the same source as the digital image in the center. If so the print is a very poor reproduction.

 

So the question is, how is that print being made? And for that matter, exactly how did you make the posted center image? What format were the digital images supplied by the contractor?

<p>I have encountered a similar situation when printing digital files. Consider that a gigantic digital file contains far more information than even a display monitor can show. Likewise, the digital printer will be presented with far more information than it can reproduce. The display board and the monitor software discard data. Likewise the print engine and its related software also will also discard data. You have no control over what the software discards. To fully reproduce meticulous image files you will need specialized software that you can control. Sorry, I have been away from the field too long, you must seek advice from someone with up-to-date knowledge. </p>

<p>Digital printing equipment is generally built to print where the fine detail is limited to about 300 dots per inch, which is pretty near as far as it needs to go for normal human vision. Contact prints from film can go way beyound this level of detail.</p>

<p>You can ask the printer how many dpi their equipment goes to, you may find commercial gear going to 450 or even 600 dpi, but probably not much further; there is little demand for it. I think your best option is to simply have them make larger prints.</p>

<p>Thanks for the responses. I think Bill is on to something. I suspect that the bottleneck is both the final printing area (which necessarily has to be less than a square foot, so that I can insert the images under the stereo scope), and the dpi of the printer. And as Alan has noted, there is probably a lot of digital info that gets wasted (for the prints, at least; we also use the digital info on our network, where we can easily zoom into the detail). <br>

Floyd, the center image was made via a screen capture after I had zoomed into the digital image enough that it was about the same scale as the other two. And the digital image was originally a gigantic tif file (4 gigs, I think), but later transformed into a much smaller sid image (about 350 megs). <br>

I will next ask the contractor what type of printer they used. </p>

 

<p>Like I always said if I were to make a 4x6 print from my 35mm negative with my enlarger there is no way any digital image in the size of 4x6 can have the same amount of details. Of course when it gets to about 8x10 then 35mm film lose out. So digital has the advantage when printing in large size not small size print.</p>

<p>So I found out that they used a Noritsu 1600 for the printing. It's listed as having a 400 dpi print output (though the contractor said that they just used 300 dpi, and the spec sheet says nothing about other dpi's). <br>

The contractor (Aerophoto) specializes in aerial stereophotography, so I'm puzzled as to why they wouldn't print to higher dpi's. On a daily basis, I use a mirrored stereo viewer with 4.5x magnification, so that's why the extra detail on the prints is critical.<br>

I see on this thread that higher dpi printers are around: http://www.photo.net/digital-darkroom-forum/00POtq<br>

But no one mentioned using a loupe to assess the difference. Has anyone here ever experimented that way?</p>

Hey Evan! Lets try to sort some of this out!

 

Digital printers don't do more than 720 Pixels Per Inch (a better term than DPI for reasons I'll explain) simply because the human eye can't see detail finer than that. HP and Canon printers (consumer and professional) print at 300 PPI for photographs and at 600 PPI for high resolution line drawings or text. Epson uses 360 and 720 PPI. Various commercial printers use resolutions from 200 PPI to 406.4.

 

You will see "DPI" values as high as 5670 listed for a variety of inkjet printers, but that is where each ink nozzle is considered a single "dot", and each pixel is a matrix of 8x8 or 16x16 dots. Hence a printer that is listed as 5670 DPI is in fact printing 720 PPI using an 8x8 matrix of colors to produce each pixel. That can cause significant confusion!

 

The problem you have is the need to use a stereo viewer with magnification. You are probably going to see individual pixels on a 12"x12" image using 4.5x magnification if it is printed at 300 PPI.

 

I'm not at all familiar with a sid image format. And I'm not sure if you meant Giga Pixels (image size) or Giga Bytes (file size). Pixels is an exact quatity, but if that is file size it might be compressed by as much as 2:1 in a TIFF file, and perhaps more in a sid format.

 

Whatever, these are seriously large images, almost certainly in terms of both size and resolution. If you can view it sharply on screen from the digital file, it absolutely can be printed with that resolution on paper too. But it will either be one huge piece of paper or a huge stack of small pages!

 

Here's the deal, if you want a 12"x12" print that is just as sharp as the digital display, then for a 300 PPI printer you have to crop out 3600x3600 pixel sections of the image and print each of them individually. For a 10"x10" print, 3000x3000 pixel sections.

 

Be aware that a lot of printing software programs are not very clear about whether an image is resampled or not. The print you have has clearly been resampled, and not with a particularly good software algorithm either. There are two things to keep in mind about resampling. First is that downsizing an image (keep the entire scene, but make the pixel dimensions smaller) absolutely will reduce resolution by the same ratio as the size reduction (it is essentially a low pass filter and removes high frequency spatial detail). Any time that is done the sharpness of edges is changed, and usually a pass with an Unsharp-Mask tool is useful. The second thing is that upsizing cannot increase resolution because it has to manufacture new data, but cannot add detail that did not exist. If is best done with an entirely different resampling filter that downsizing. Generally a pass with a Sharpen (high pass) filter is more beneficial than Unsharp-Mask (but both will probably be somewhat useful for either up or down sampled images).

 

A highpass sharpening tool works on something like a picket fence that is a sequence of multiple tone changes. An Unsharp Mask tool considers the picket fence to be the average of those tones and does little to the pickets, but it will see the single tone change at the top of the fence (for example separating the fence from the sky). In an image that has been made larger it helps to differentiate between the pickets, while in an image that was downsized the pickets might be too close together to even see anymore, but every single edge will benefit form changing the contrast around it with Unsharp Mask.

 

It would appear that what you want is maximum resolution. That will only happen without any resampling, though one or both sharpening techniques may help at least some. The problem then might be that you get too little (or maybe too much) ground surface area covered in each single 12x12 print. You will have to decide what works best for your purposes. It might be that downsizing, to put say 5 or 10 times as much ground area onto a single print, would be convenient for initial analysis to locate things of interest, and then a full resolution that is much less ground area on each print might be used to detailed analysis.

<p>The clear answer is no. I have actually scanned aerial 9x9's on my drum scanner, a high end Aztek Premier. There's plenty of detail in there. There were scanning devices made to scan these things in - with the film still on a roll, there were also printing devices made to do the same. None of them were designed for high resolution or high quality. <br>

The people who made the print didn't even bother to sharpen the image. The digital image is clearly sharpened and has had the contrast enhanced. If you take the contact print, there is at least as much detail. With sharpening and a little curve-ing one could get to the same image. There is no reason to lose detail in the scanning process with a proper scanner.<br>

Hope this helps.</p>

<p>Thanks guys. The other restriction I have to live with is the total number of prints. Our county's surface area at a scale of 1:20,000 (plus some overlap for the stereo effect) gives me about 1,000 fairly thick sheets. And we do this every 3 years. So I have to watch our filing cabinet space. Digital is fine for comparing what happened out in the county between 2010 and 2013 (for example), but for a quick stereo assessment of things in 3-D, nothing seems to compare with a couple of good prints (I have seen 3-D stuff on the screen with the high-tech goggles that the big boys in the provincial building have, but I think that that is way out of our budget range). <br /> I guess the answer I was looking for was the 720 dpi that Floyd mentioned. If my math is correct, that gives us about 5.7 times the amount of detail as the 300 dpi print. So I will hunt around locally for a place that will do that, get a sample, and report back.<br>

I should also mention that the file sizes I talked about earlier related to areas larger than that which gets printed off on the 9" x 9" sheets. Our GIS guys amalgamate the individual photos to make a bigger one of a single township. And the whole lot for the county has to be carried around in a multi-terrabyte hard drive. But suffice it to say that we have more than enough digital pixels to play around with. <br>

<br /> <br />Thanks again.</p>