Digital Camera resolution vs Photoshope resolution

[Zebra]

I'm currently hinting strongly at Mrs. Z to get me a digital camera for Christmas.

This hinting will include circling items in catalogues and such.


However I'm looking at these digital cameras and they talk about Megapixels and then they talk about resolution as in "takes up 1200 by 1600".

And I'm thinking, that's not the resolution, that's the size.


You see I do some 'graphic' work using mostly photoshop and when something gets set off to the printers it has to have a resolution of at least 300 DPI. So to me DPI is resolution and camera makers don't seem to publish the DPI their cameras do.


So my questions.

What's the deal here? Is an image at say 3.1 megapixels going to look good when I bring the DPI up to 300?

Are there cameras that shot at other than 72 DPI?

Thanks.

[panache45]

The "1200 x 1600" is the measurement of the image in pixels. That number, along with the resolution, will give you the actual measurement of the print, in inches. For example, if your resolution is 100 ppi (not dpi), your image size will be 12 x 16 inches, and if your resolution is 200 ppi, your image size will be 6 x 8 inches, and if your resolution is 300 ppi, your image size will be 4 x 5-1/3 inches.

Once you've got the image in Photoshop, you can adjust the resolution or size to whatever you want. Of course, whenever you change resolution you should also sharpen the image.

The print resolution, dpi or dots per inch, is a totally different issue.

[pulykamell]

I would qualify what panache said. When you change resolution in Photoshop, make sure you have Resample Image OFF if you are going to a higher resolution. Otherwise, you're simply increasing the size of your pixels. You can get away with slight enlargements, but anything more than 120% or so and it starts becoming noticable.

I totally disagree about the sharpening advice, though. I almost never sharpen digital images -- even a little sharpening tends to make things look overly "stair-stepped", i.e. blocky in that digital way. Unsharp masking is mostly used for flatbed and film scanning, where a slight fuzziness is the image is inevitable.

[Colophon]

However I'm looking at these digital cameras and they talk about Megapixels and then they talk about resolution as in "takes up 1200 by 1600".

And I'm thinking, that's not the resolution, that's the size.


You see I do some 'graphic' work using mostly photoshop and when something gets set off to the printers it has to have a resolution of at least 300 DPI. So to me DPI is resolution and camera makers don't seem to publish the DPI their cameras do.

Well, they can't talk about the absolute resolution, because they don't know how big the finished image is going to be! Are you going to be printing at 6" x 4", 7" x 5", 10" x 8"....?

Basically, you should assume that 300dpi of native resolution (ie before upsampling) will give you prints that are too all intents and purposes indistinguishable from film prints. (In fact, I think they tend to look better).

So if you have a 1600 x 1200 pixel image, you could print at 1600/300 = 5.33" along the long side of the print.

In practice, you can print at twice this size and still get good images - I have a 1600 x 1200 camera and have made great pictures up to a foot along the wide size, with a bit of judicious resampling.

It's also worth remembering that digital cameras tend to have an aspect ratio of 3:4, as opposed to 2:3 of 35mm film. So if you print on standard photo paper, you'll lose a bit of the image at the top and bottom, or leave white strips at the sides.

[GaryM]

r_k mentions that digital cameras tend to have an aspect ratio of 3:4 rather that the 2:3 of 35mm which most of us are familiar with. And that's correct. But some cameras have a menu selection that lets you choose the 2:3 ratio format. The Nikon 995 that I currently use has this choice available. Not sure which other, newer, model have this feature. You can easily change aspect ratio from shot to shot with a menu selection. Of course you can select the acpect ratio of the crop tool in photoshop and get the same effect.

[Zebra]

Thanks

r_k That's the point that I didn't get but do now. The divide pixel size by dpi to get actual size.

Thanks.

[handy]

I can't add much to the above but have a look at Target's ad this week they have a great bundle, a HP Photosmart Camera, HP Photo printer (prints without a computer) & 32M memory card, all for $189.00 Camera is usually $150, Printer $150...

[Musicat]

Here's a photo spec primer. There are three specs for a digital image, in each dimension: dots, inches, and DPI (dots per inch).

Of course, inches can be any measurement, and dots are usually called pixels (picture elements).

There is a mathematical relationship between dots, inches and DPI:

dots / inches = DPI

Using simple algebra, this can be expressed as:

DPI * inches = dots

or:

dots / DPI = inches

As a broad rule, printers respect the number of inches, and screen displays respect the number of dots (of course these behaviors can be altered, but I think of this as a "native" characteristic).

In photo editing software, it is possible to change any one of these parameters without altering any data, or resampling, which DOES alter the actual data. The mathematical relationships given above will always be true.

Example:

300 DPI, 1 inch (assume both height & width). This image, if blasted out to a printer raw, will print one inch wide. If displayed in a browser, will be 300 pixels wide.

Altering the dimensions without resampling could give you 100DPI, 3 inches -- no data changed (was 300 dots, still 300 dots). Sending this raw to a printer would show a 3 inch pic at a lower quality, but a browser would still show it at 300 pixels wide (we didn't change the number of pixels, did we?).

This same image could be resampled, which WOULD change the number of pixels (up or down).

[olefin]

Buying a digital camera.... get one with at least 4 Megapixels if you can afford it.
Rechargeable battery a must.

A good place to compare features.
http://www.steves-digicams.com/hardware_reviews.html

[KenGr]

Originally posted by olefin
Buying a digital camera.... get one with at least 4 Megapixels if you can afford it.
Rechargeable battery a must.

A good place to compare features.
http://www.steves-digicams.com/hardware_reviews.html

OK, I'll throw in a couple of personal opinion items here.

For those who take snapshots but still expect to occasionally make an 8 x 10, 3 megapixels is a reasonable size. I did some comparisons between my Canon A70 and 35mm and came out with some surprising results. You can see them here:

Digital Comparison (www.kengreen.us/photo/digital_comp/digcomp1.htm)

Also, I would say that the ability to use standard rechargeable batteries is a must. You can buy rechargeable AA NiMH batteries very cheaply now and the savings (over a dedicated rechargeable battery) plus the ability to use a set of alkaline AA's in an emergency make this the way to go. When I was comparing digital cameras, I severely penalized those with special dedicated batteries.

[SPOOFE]

I did some comparisons between my Canon A70 and 35mm and came out with some surprising results.
Question: What did you use to scan the film? I've been digging into film scanners for the past six months (a buddy of mine that has 50,000+ negatives lying around wants to get one).

Anyway, when it comes to a digital camera, 3.3 megapixels is what I consider should be the base minimum if you want anything more than spiffy pictures for your webpage (if that's all you want, just stick with 1.3). But if you want good digital images for 8x10s, to send to relatives or somesuch, or to take the family photo, get at least 5 megapixels.

[scr4]

One thing to keep in mind: pixel count is not always a guarantee or even a good indication of image quality. In an ideal world, a camera with a 1200x900 detector can resolve 600 vertical lines (two pixel columns to resolve one line: one black and one white). In reality, lens design, color filter design and image processing algorithms all degrade the image compared to the ideal. (Which isn't to say that camera designers are being sloppy, of course, there are always compromises to make.)

As a corollary, even if you just need a 1-megapixel image (e.g. web site work only), you are better off using a 2-megapixel or better camera and resizing the image down to necessary size. On my 1024x768 monitor, images from my 3-megapixel camera look noticeably better than those from my older 2-megapixel camera, and far better than those from my even older 1-megapixel camera. (Canon A70, Olympus 2100 and Nikon 900, respectively).

It also means you should look at sample images rather than pixel count when comparing cameras. Fortunately there are many good review sites who post sample images, like dpreview (www.dpreview.com/) and Imaging Resource (http://www.imaging-resource.com/).

[KenGr]

Originally posted by SPOOFE
Question: What did you use to scan the film? I've been digging into film scanners for the past six months (a buddy of mine that has 50,000+ negatives lying around wants to get one).

Anyway, when it comes to a digital camera, 3.3 megapixels is what I consider should be the base minimum if you want anything more than spiffy pictures for your webpage (if that's all you want, just stick with 1.3). But if you want good digital images for 8x10s, to send to relatives or somesuch, or to take the family photo, get at least 5 megapixels.

As I noted on my webpage, I have a Minolta Dimage Dual. At 2800 dpi and USB 2.0 interface, it's a tremendous bargain at less than $300. However, doing thousands of negatives would turn into a long term job. I'm not sure if there is something a lot quicker out there.

There are advantages to 5MP systems as far as cropping margin, and they probably tend to have somewhat better lenses, but I don't think most people will see a difference in 8 x 10's. At least that's what I've concluded in my work with the A70. It's not just megapixels over 3 MP. I'm really looking for a full 35mm system body converted to digital at a reasonable price. I'm not so concerned if it has 3MP, 6MP or 12MP as I want a full sized sensor so the lenses work the way they are supposed to. (From what I understand of the technical limits, it probably will be about a 12 MP camera to make this work.)

[Algernon]

I'm really looking for a full 35mm system body converted to digital at a reasonable price. I'm not so concerned if it has 3MP, 6MP or 12MP as I want a full sized sensor so the lenses work the way they are supposed to. (From what I understand of the technical limits, it probably will be about a 12 MP camera to make this work.)Ken, could you say more about this? I have resisted the move to digital from SLR 35mm for two reasons.

First, the time lag between depressing the shutter button and the capturing of the image in digital is (for the cameras I've tried) unacceptably long.

Second, I like my Canon interchangeable lenses. I've seen some recent advertisements that Canon has a digital camera now that can use existing lenses. Your comments lead me to conclude that there is more to the story. Can you elaborate?

[handy]

I have a Fuji Finepix 1.3 If I run the photos through a photo program auto adjust the photos stay the same. Now that's what I call a great camera.

BTW, if you're doing 2800 dpi x 2800 dpi your image file size is going to be 7,840,000 dots per square inch, quite a large image file size.
e.g. 8 x 10= 80 x 7,840,000 = 627,200,000

[scr4]

Algernon, Canon has several digital cameras that use the EOS series interchangeable lenses. But most of those cameras use detectors that are smaller than 35mm film, simply because large detectors are extremely expensive. So if you put a 50mm lens on it, it'll act like an 80mm lens (have the same view angle). This might be good if you like telephoto lenses, but not good if you paid big bucks for a quality 20mm lens. There is one model, the EOS 1Ds, which has a full-frame (35mm size) detector but that's an $8000 camera.

The same is true for Nikon. Kodak makes a full-frame (35mm detector size) digital body with a Nikon F lens mount. Nikon and Fujifilm make digital bodies with smaller detectors.

By the way, I don't notice any shutter lag on my Fuji S2 digital SLR camera. I'm not into action photography though, so I may not be as sensitive to this as you are. I believe the Imaging Resource web site has measurements of shutter lag on many of their reviews, if you're interested.

[scr4]

handy, KenGr is talking about a film scanner. A 35mm film scanned at 2800 dpi is 3860x2750 pixels, or approximately 10 million pixels. It's not excessively large.

[Musicat]

Originally posted by Algernon
First, the time lag between depressing the shutter button and the capturing of the image in digital is (for the cameras I've tried) unacceptably long. Turn off the automatic focus (and maybe automatic exposure on some cameras?) and it'll work just like an SLR.

[Algernon]

Musicat, that may be true, but I'd like the shutter response to be similar to a film SLR with auto focus and auto exposure. It's pretty darn close to immediate with a film camera. With the digitals I've tried, the lag is significant.

I'll go to the camera store and try out the Fuji that scr4 recommended and see if it is better.

[scr4]

Originally posted by Algernon
I'll go to the camera store and try out the Fuji that scr4 recommended and see if it is better.
Um, actually I'll have to take that back. I just dug out my old film camera (Nikon F90x) for comparison and it does feel faster than my digital camera. I still think the lag on the S2 is acceptable, but compared to the F90x it feels as if the shutter button is "sticky" or "heavy." It's not something I perceive as "lag" per se, but it's there.

[pulykamell]

There is no real noticeable lag on the high-end digital SLRs, such as the Nikon D1X, D1H, D100 or the Canon EOS series. This is what the pros use at sporting events. Of the bunch, the D100 is the cheapest, retailing at around $1500 or so.

These cameras work very much like their 35mm counterparts the main difference being that lenses act 1.5x their normal focal length. And the frames per second are slightly less. Other than that, there's not much difference between taking pix with an F5 and a D1X.

[KenGr]

Several people have answered correctly about the digital systems based on 35mm bodies. The affordable ones have small sensors, shifting effective focal length. When my $600 20 mm lens act like a 35mm focal length, it's just not what I had in mind.

I'm guessing we'll see bodies with full size sensors under $1000 within two years.

The problem with large sensors is interesting. I questioned why we couldn't have a 6 MP sensor that was the full size of a 35mm film frame. It turns out the optimum size of the sensor elements ("pixels" I guess for lack of a better term) is such that you need to go up to about 10 or 12 MP for 35mm equivalent. Larger "pixels" result in excessive noise and image degradation. So the options are a large sensor or a completely new system that uses short focal length lenses.

[scr4]

Originally posted by KenGr
It turns out the optimum size of the sensor elements ("pixels" I guess for lack of a better term) is such that you need to go up to about 10 or 12 MP for 35mm equivalent.
Do you have a cite for this? This doesn't sound right to me. Thermal noise scales as pixel area ("pixel" is the correct term, by the way), and readout noise is pretty much constant regardless of pixel size. Signal also scales as pixel area, so larger pixels should result in lower noise. On the other hand if you try to make the pixels too small, readout noise starts to dominate and S/N ratio goes down. Astronomical CCD detectors often use 10 or 15 micron pixels. With 15 micron pixels, a 35mm-size detector would be 2300x1750, or 3 megapixels.

Usually the limiting factor is the cost of making a large chip. Typically with processors and other ICs, cost per chip decreases over time because new technology allows smaller chips to do the same job, by packing more transistors per unit area. Cost per area hasn't changed much. But if you do that with a CCD you end up with smaller and smaller detectors with smaller pixels, which is exactly what's been happening with consumer (point & shoot) digital cameras. A 35mm size CCD has 6 times the area of an Athlon XP die, and remains expensive. On the other hand, if you're willing to pay for such a large chip, you don't save any money by putting fewer pixels on it. Whether you fill the chip with 3 million 15-micron pixels or 12 million 7.5-micron pixels, there isn't a huge difference in price. Which is why we may never see a full-frame 3-megapixel camera.

[rjung]

Just one minor contribution from a neophyte here: when buying a digital camera, make sure it has a good flash. My otherwise wonderful Canon Powershot S40 has a dinky flash, which makes most indoor photos a bit on the dim side. Given how digital cameras have more "noise" visible the darker the image gets, this is a definite minus IMO.

[vasyachkin]

when in photoshop, you can go to "image size" or "canvas size" and change the units from DPI to Pixels.

alternatively use a pocket calculator to multiply DPI by size of image in inches to get pixels.

not rocket science :)

[Early Out]

Originally posted by r_k
It's also worth remembering that digital cameras tend to have an aspect ratio of 3:4, as opposed to 2:3 of 35mm film. So if you print on standard photo paper, you'll lose a bit of the image at the top and bottom, or leave white strips at the sides. Another thing to remember on the subject of aspect ratios is that none of the standard paper sizes, 5x7, 8x10, 11x14, or 16x20, has the same aspect ratio as either 35mm film or digital cameras. In fact, those paper sizes don't even have the same aspect ratio as each other, other than 8x10 and 16x20, which are both 4:5. When you print your image to any standard size photographic paper, you either lose some of the image in one dimension, or you have some white paper along an edge or two.

If you take your images (either electronically or as negatives) to a good processing lab, they can do what's called "full frame" enlargements. So, for example, you can get an 8x12, where the aspect ratio matches that of a 35mm negative. If you ask them to print a full-frame 11x14, they trim the white edges, and you end up with a print that's actually 9.33x14 (2:3 aspect ratio).

[KenGr]

I've seen several sources that say that although larger pixels have lower S/N ratio, that doesn't get much better after a pixel pitch of about 6 microns. As pixels get larger, you begin to get problems with aliasing and aberations. I think the most in depth source on line for this and a lot of other photo stuff is Norman Koren:
Norman Koren (http://www.normankoren.com/Tutorials/MTF7.html)

Here is a summary paragraph from that web site:
The optimum pixel size for high quality imaging seems to be in the 6-9 µm range. Larger pixels have problems with aliasing and can't take advantage of high quality lenses. Smaller pixels have more noise and less dynamic range and sensitivity, though they can still produce decent images. They are used in compact and low cost cameras-- 2-3 megapixel digital point-and-shoots with sensors as small as 5 mm diagonal as well as the sophisticated 5 megapixel cameras listed above. Digital SLRs will stick with 5-9 µm pixels and evolve towards larger sensors with more pixels. A 24x36 mm sensor with 16+ megapixels (7.4 µm or less pixel spacing) will have performance approaching medium format (see the analysis, below), but it won't come cheap for quite some time.

I am aware that astronomical equipment has larger sensors but my understanding is that these are actual pixel arrays, typically a square of 4 pixels linked. I'm not entirely clear on why this is done but it may have just been a way to avoid the optical problems without increasing the amount of data that needs to be handled. Video cameras have used this approach to get faster response and higher sensitivity, since they don't need the high resolution.