Recently I was at a local camera shop, and they had a number of photographs on a wall from a recent 'camera club' day out. Looking at prints that were only 5x7 inches I was struck just how "grainy" many of these images were when printed at such a small print (given their megapixel ability). A 5 megapixel camera should be able to print nicely up to 8x10 inches, so smaller than this should not be a problem.
The problem is that the image quality is low even though the image size is big.
The problem is, not all things are equal.
Well certainly there are advances, but in many ways things are kind of going nowhere in many ways nothing has really changed in digital cameras since about 2002. Image sizes are going up, but sensors are not getting any bigger. So image qualities are going down on most cameras except the DSLR's.
Back in 2001 a good compact camera could compete with a DSLR for image quality. A US$5000 top of the range professional DSLR cameras (like the Nikon D1) produced images only slightly superior in quality and size as those from compact (see for instance Thom Hogan's review). But today there is just no way that you can compare them. The reason for this is that image quality is being lost by using smaller sensors and squeezing more megapixles out of them. Because only megapixels seem to be the important marketing factor
Just as slicing the same pizza into more slices means smaller slices, divding the same sized sensor into more pixels means each pixel is getting less light.
This is exactly what has been happening with most digital cameras since about 2002.
In this chart you can see that while the Megapixels have been going up (from 2 to 8),
sensors in most cameras have not got any bigger in their size since 2002, in fact they have shrunk a little.
This means that each pixel of your camera it will get less of the light from the
scene, and that means a lower picture quality.
This is explained in more technical detail at Roger N Clarks website. If you are not scared off by the large amount of numerical data presented in there, he shows clearly why lager sensors (and therefore large pixel sensor sites) mean better images. Size matters, its not just the quantity of megapixels, its the size of the sensor.
So in this page, I'm hoping to add to the understaning people have on cameras. Hopelfuly if more people become aware of this it might help to reverse this silly trend and help people to understand that size matters, not just of the image, but of the sensor which is capturing that image.
With a common screen size of 1024 x 768 pixels, every digital camera from 2 megapixels up will make a picture that's much too big to see on your screen. Normally software reduces these images to fit onto the screen.
But when we get our images printed its different, to the screen. The printing machine can vary the amount of pixels per inch, that is where the DPI value means something. It is meaningless on screens (where because we can't vary the amount of pixels). In a print, the more pixels per inch the more detailed the printed picture becomes(assuming your picture is detailed to begin with) and the smaller it will be too.
This is what I am calling print detail, the number of pixels per inch that are printed on the paper.
People argue over the amount of pixels per inch needed, but it will vary depending on things like the distance at which you'll look at the print, and the sharpness of the image you have in the first place. I find that anything from 150DPI to 300DPI is a good range for photographs.
The chart below shows the relative size of print that can be made from an image based on how many pixels it has. It doesn't matter if you print at 150 DPI or 600 DPI, if you print each 3 or 5 Megapixels at the same DPI, this is the difference in print size you'll get.
I wasn't that long ago that a 5 megapixel image was considered a good size, even at the time of writing some DSLR cameras are still around 6 megapixels (although 8 and 10 are emerging). Looking at this chart, the difference between 3 and 5 megapixels isn't really that much. To put numbers on this, a print from a 3 MP camera would be about 7 x 5 while a print from a 5MP camera would be only about 8 x 6. ... not much in it is there?
Yet, looking at 5x7 prints recently at the local camera club I was struck by just how noisy and grainy many of these images looked. This was quite surprising as personally I have found that only 3MP cameras such as the Nikon Coolpix 990 can give great printed images at 5x7 sizes. Are things getting better or not?
The present trend is to try to squeeze more out of less. DSLR cameras are regarded as the bench mark of quality, importantly they have bigger sensors than the compacts. Even Canon's professional "pro-sumer" compact has had its sensor shrink from the G3 to the G10.
How much? well comparing the sensor of my old Coopix 5000 to my 20D is like this:
| the sensor sizes | the image size we get from the cameras |
|---|---|
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This should show you exactly how much more we are magnifying the little image falling on the small sensor to make an image nearly as large as that of the DSLR. With modern compact cameras the size ratio is even worse. In the figure below I have compared 35mm (Nikons FX format or Full Frame as it may also be called) with the sensors of my older Coolpix 5000 (2/3") and the newer compacts which are smaller sensor but more megapixels.
So you can see that the sensors in cameras like Canon's 10 megapixel G7 is actually smaller than the one in my 5 megapixel camera, while having a bigger image pulled out of it.
No wonder the DSLR image is better. But it doesn't have to be this way, we are not constrained to have small sensors in compact cameras.
Looking at this image, it would at first seem that it was taken during the day,
but this is actually taken at night by the light of the full moon from my verandah.
The camera (a 2 megapixel camera) is set to it highest ISO setting(ISO 320).
The camera was a
Coolpix 950,
which when it was released in 1999 was one of the top cameras but it's
not a DSLR.
I was quite surprised when I reviewed this photo to see how blue the sky was, when to my eye it seemed just a normal evening. Clearly the blue cast of the sky can appear in any picture as long as there is enough light. Anyway, back to the image quality, notice how clean it looks?
There is almost no noise in the image, compared to the images I was seeing in newer 5 megapixel cameras today (the quality is almost like a DSLR). Now, it is this lack of noise which effects the image quality, and makes prints from these cameras look better than noisy newer cameras.
As an example of the noise effects on image quality, I took a quick test image from my Canon A520. This image unlike the one above did not push the camera to its limits, as the exposure time was significantly shorter. This is important because the longer the exposure the more likelyhood of noise. Even given this, and scaled down for the web it looks like its grainy and noisy.
Now on close inspection this image shows quite a lot of noise. Sure sure, everyone knows that compact cameras have noise at higher ISO.
Ok, look at the side by side of these two images below. The older camera has much less noise than the newer one. Even though the exposure time was much longer.
| segment from 1999 camera | segment from 2005 camera |
 |
 |
The exposure for the Canon was only 1/5th of a second compared to 8 seconds that the Nikon used. Yet despite having an exposure time more than 6 fstops longer, the image from the nikon is so much cleaner.
The Canon has a smaller sensor than the Nikon, so it divides the light falling onto its 4 Megapixels rather than the 2 that the Nikon does. This shot might look noisy at a small size but the details show a noise fest ... Yuck, no way you could make a decent print from this one.
This is what I mean when I say that we are kind of going nowhere in the development of digital cameras.
Thom Hogan pointed out in his review of the 990, not everyone wants spend US$5000 on a camera, and this has been addressed with amazing price falls in DSLR cameras. New DSLR's now cost half what compacts like my Coolpix 990 did when it was new.
However personally, after using "pro-sumer" quality digital compact cameras, I'm well and truly a believer of this new format. These cameras offer fantastic image making tools which extends the ways that I can make images. I don't want to abandon my SLR style camera, rather I want to augment it! With a competent compact portable image making tool. For me the advantages of a compact, high quality image camera are:
So compact cameras are getting the bum end of the deal, and if you want to get good quality images from a current digital then you really have to buy a DSLR.
Not everyone wants or needs a big heavy DSLR for taking their pictures. Its not just me, other photographers out there are also wondering why we can't have a compact cameras that make good images. Thom Hogan also has a page talking about an ideal "compact camera", and suggests that there's thousands of people writing to him agreeing that they want better compact cameras too. What ever happened to companies being interested in the customers?
By not having access to RAW, we are not getting the best image from the sensor we have. Back in 2003 (over 4 years ago now) I read an article by David Burren on how to get better images from an old (Nikon Coolpix 950) by using RAW captured from the sensor. The differences were startling.
This changed my views of what was happening inside the camera, and unlike film based images, , there is opportunity to modify what has been captured by the sensor easily. I realized that there were other important factors involved in putting together those pixels. That grid of sensors sees each of the colors separately, so these can be moved from where they were recorded, to where they "should be". Having played with the Adobe RAW converter, I found that issues such as chromatic aberration can indeed be corrected. Common digicam problems such as "color fringing" were probably created by "chromatic aberration" which just like the Hubble telescope, could be 'fixed' in the software RAW conversion process.
Also some of that the noise that's apparent in many images is actually an created by the signal processing used in the camera that converts the sensor data to a JPG file. In another article I discuss the 'noise' introduced by many in-camera systems.
So to Mr Camera maker, please, consider that not everyone wants ONLY a DSLR, and that if you put decent sized sensor in compact camera and give us back decent compact cameras, you might just sell more of them.