Beginner Tutorial 4

It is easy to be impressed by the huge number of megapixels (MP) offered by the latest digital cameras – and even some smartphones! However, there are more things to consider before you choose which camera to buy, as image performance is determined by several other factors such as sensor size.

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Does sensor size or pixel count make a difference?

One of the great subjects of debate about modern digital cameras is pixel count and/or sensor size.

All your friends will have an opinion on this, but rarely do you get a true answer as to what the numbers mean and why!

With the lens removed, you can see the rectangular image sensor.

With the lens removed, you can see the rectangular image sensor.

So, let’s explain a little about what pixel count means and how it relates to sensor size and picture performance.

Each pixel represents an element of a digital image that, when grouped together, create a recognisable picture. In the case of a digital camera, the information for each pixel is gathered by corresponding, light-sensitive ‘photosites’ arranged on the surface of the camera’s image sensor.

There are usually more photosites on the sensor than pixels ultimately making up the final image, but for simplicity we’ll refer to each photosite as one pixel. The resolution of the image depends on the number of pixels and the quality of the information each contains. So one may think that more pixels means better quality pictures – but this is not always the case…


Size vs. quality

Image sensors come in a number of sizes and relate to the size of lens and the distance from the back of the lens to the sensor.

The smallest sensors are used in ultra-slim smartphone cameras and increase in size up to the professional Digital SLRs that have sensors the same size as an old 35mm film frame (so called full-frame).

Medium and large-format cameras also exist with even larger sensors, but these are generally used for specialist work (and priced accordingly).

Sensor Size text

Image Sensor Size Comparison - Illustrations shown to scale

Image Sensor Size Comparison – Illustrations shown to scale

The size of the sensor divided by the number of pixels/photosites determines the size of each pixel. Modern digital sensors typically contain millions of pixels – 1 megapixel (MP) = 1m pixels – but smaller sensors limit the number and size of pixels. This diagram shows a selection of common sensor sizes used in cameras today.

On the image sensor, larger pixel size means more light photons get captured, resulting in a better ‘dynamic range’ (which we shall examine in later tutorials) and better signal quality – outweighing unwanted picture ‘noise’. Also, heat building up on the sensor is more easily dissipated; this also reduces noise.

The tiny sensors in compact cameras often have the same pixel count as the larger ones in interchangeable lens systems – but each pixel must be smaller and mounted closer together. This results in less light-gathering capability and makes heat-dissipation more difficult.

Megapixel comparisson

The most noticeable improvement in picture quality when comparing compacts and system cameras is seen when shooting in low light. The larger sensor is better able to capture the available light and generates much less noise in the final images.

To put this in perspective, a ‘Micro Four Thirds’ sensor containing 16 megapixels has the same size pixels as an ‘APS-C’ sensor with 24MP, therefore they both have the same picture performance potential (right). Simply adding more pixels to a sensor is no guarantee of a better picture and is likely to reduce the performance rather than improve it.

So, if the size of pixel is more important than their number, why are manufacturers offering more and more megapixels on their devices?


Megapixels vs. quality

Because each pixel is a tiny part of the whole picture, it is important to have enough of them to capture every tiny detail. The more parts of the picture we have, the more detailed the picture becomes.

You can appreciate the improved picture when looking at HD compared to a standard TV – because an HD signal and HD TV screen contain about five times as many pixels as the old standard. However, HD TV pictures are made up of only 2 megapixels – while digital stills cameras now offer up to eight times that many. What matters is what you want to do with your photos – whether the resolution will be good enough to see the detail you want.

So, a 2 megapixel HD TV picture looks amazing, but if you print it at the same size as the screen, it will look terrible – because printed ink needs a certain density for our eyes to view the individual colour dots as a merged image.

The density widely used for good-quality photo printing is 300dpi (dots per inch). In printing, dpi is not the same thing as pixels per inch (ppi), but for our purposes we shall equate the two.


Printing sizes vs. pixel count

4” x 6” @300ppi = 1200 x 1800 = 2.16MP
5” x 7” @300ppi = 1500 x 2100 = 3.15MP
8” x 10” @300ppi = 2400 x 3000 = 7.20MP
8.25” x 11.75” (A4) @300ppi = 2475 x 3525 = 8.72MP
11.75” x 16.5” (A3) @300ppi = 2475 x 4950 = 12.25 MP

Once you know the pixels per inch needed for good-quality printing,
simple maths tells us how many megapixels are required for different
paper sizes. The table (right) shows popular photo paper sizes and how many pixels are required to achieve good quality prints.

As you can see, most modern cameras can produce an image that will
print up to A3. But don’t forget that if you want to crop, this could reduce
the pixel count by as much as half –which is why cameras exist offering
12MP and more. However, if you are planning to send pictures for
printing, some companies work on 200 or even 180ppi, so it is best to check with them first.

Of course, many photographs these days are never printed. If you are
only going to view them on screens, there is no need to shoot at
maximum resolution all the time. This can save you a lot of storage space
and make images easier to email.


It’s not all about the sensor

We have learned that the size of the sensor makes a big difference to the size of the pixel, and the number of pixels has a bearing on the size of the image. But neither of these, on their own, ensures good picture quality. The quality of the lens as well as the image processor, in conjunction with the sensor determines the overall picture quality.

Lenses must provide high optical performance for accurate image reproduction, with high light transmittance and low distortion / colour aberration.

Next, the image processor is the engine driving the cameras performance. It must be capable of quickly processing sensor data – applying correction and filtering noise – then converting it into the images that are saved on the memory card.

So, the camera that produces the best result will use high-quality optics and a sensor of the optimum size for maximum light capture, yet offer enough pixels to capture all the brilliant detail of an image – and incorporate cutting-edge image processing to deliver the final result at the amazing high speeds demanded by today’s photographers!


The LUMIX Advantage

The LUMIX G’s excellent image quality is built on three pillars: optical performance, derived from Leica lens design; optimum system and sensor design; and image processing experience.

Panasonic’s lens and camera manufacturing expertise garners worldwide acclaim, with the Micro Four Thirds system construction and sophisticated lens accuracy ensuring light arrives on the sensor at a perpendicular angle – the most efficient way for it to capture images (see below).

The powerful Venus Engine processor then takes over – interpreting, refining the image data with complex algorithms that control textured areas, edge processing and tonal reproduction.

Remember the points raised in this tutorial – don’t just buy the highest megapixel camera you can, as you now know there’s a lot more to it than that!

Sensor comparisson2

Classic lens design without high refractive glass lenses leads to light arriving in an angle that the sensor cannot receive

Sensor comparisson1

LUMIX G lenses are designed to have the light hitting the sensor perpendicularly

 

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Written by Steve Lucas for Panasonic ©