Lawrence Photographic



Back to Articles Page

   Optimum Image Quality!


 Last Updated  - 25th June 2013

It is great fun to just shoot camera produced jpeg images, especially for family events and social trips but for any serious work, I prefer to shoot ONLY 'RAW' files. They provide the 'optimum' starting base for image quality and by using the correct software to post process them, I can control the final output for printing.

There are limits as to the amount of editing control that a camera can apply to the final camera jpegs bearing in mind that some users will edit their own settings in the camera menu (saturation/contrast/noise reduction/sharpness) which may increase the final camera jpeg image quality but also may decrease it. There is no doubt that post processing 'RAW' image files and 'tweaking' to suit (resolution/noise/print size/viewing distance) will deliver greater control and often produce a more desirable result. Very often images are judged by their appearance on a digital display (at various sizes) but in reality they should be judged by their final print on the wall.

I like reading professional reviews, following certain 'gear' forums and generally keeping up with the latest camera and lens technology. Invariably at the core of most of these discussions is the relationship between a new camera's digital sensor noise versus the final image quality at high ISO ratings. However, there is much more to image quality and in the real world, the final quality of a digital image file is determined by a number of factors which control it's production, not least -

  • The amount of available light in a scene (low light considerations)

  • Noise reduction

  • Camera exposure meter + digital sensor  

  • Lens quality

  • Subject Distance vs. Resolution

  • Camera autofocus system 

  • Shutter speed + image stabilisation' limits

  • Tripod considerations

  • The processing mechanism - prints - digitals displays

Light + Low Light
Light plays an important part in the ability of a lens to deliver optimum resolution. With low light conditions and just like your eyes, the lens will struggle to take in all the scene data, especially in the shadows and dark areas. The lens has to be opened up (wider aperture) to take in more light and in the process the resolution that the lens delivers to the sensor is usually weaker and especially if the subject distance is increased. A lens tends to have an 'optimum' aperture for 'optimum' resolution and very few lenses will maintain that resolution at wider (f1.4 - f2.8) apertures. To compound the problem of using a lens at wider apertures -
low light photography (e.g. night street shots) demands a higher ISO rating (especially for camera hand held shots) and as it rises, towards ISO:3200 and beyond, digital noise starts to creep into the image and noise reduction is applied (in camera or in software post processing) to reduce it's visibility. Even in good daylight, sport or wildlife photography may also push up the ISO rating towards ISO:3200 if the lens is forced to operate at a 'stopped down' aperture of f5.6 towards f22 due to it's design, whereas a lens with a 'wider' aperture of f2.8 can keep the ISO rating lower as the lens lets in more light.


Noise Reduction
In light conditions where the
camera sensor and the lens push the ISO rating of the camera up from the preferred ISO:100 towards the less preferred ISO:3200 (or higher) the resulting digital sensor noise invariably has to be reduced either in-camera or in software post processing. Any applied noise reduction will impact on the resolution in the image, push it too far and the image becomes mushy and loses it's resolution when viewed or printed at 100% - keep it too low and the noise remains visible. There is a fine balance regarding the amount of noise reduction versus the final image quality that can be applied in relation to the size of the printed or digitally displayed image and the final 'viewing' distance.


Exposure Meter + Digital Sensor
The accuracy of the camera's exposure metering system is essential to determine an accurate exposure setting for the light in a scene. In normal light conditions, the correct exposure will provide the best conditions for the sensor to deliver it's optimum resolution and dynamic range. Some sensors have a very high dynamic range that can operate in a large number of lighting scenarios whilst others struggle. However in light conditions that are VERY uneven like a dark foreground and a bright skyline, the exposure metering might struggle to balance the two and invariably errs on the side of a bright foreground and a blown sky where any cloud outlines have been lost in the data captured and usually cannot be recovered in-camera or in software post processing.  The photographer will take exposure meter measurements of both the foreground and the sky and select an exposure reading in-between which invariably will be an under-exposed reading (for the foreground) which in turn weakens the final image resolution. To work around this dilemma, some photographers will use a
graduated filter to darken (only) the skyline which balances out the overall exposure reading and avoids the under-exposure of the foreground. The graduated filter is great for using for even lines between the sky and the ground but if there are any high trees or building in the skyline, then their tops in the sky tend to be darker than their base in the foreground - even soft graduated filters struggle to avoid this.


Lens Quality
Unfortunately (so far) I have not had the pleasure of using a perfect lens. All my lenses have certain imperfections, and not just the kit lenses, I have some lenses which are very expensive. Lens resolution is a complicated business to judge, even by reading the reviews and the technical charts. One person's most excellent kit lens is another's nightmare. A lens has limits, like diffraction,
depth of field amongst others and it is learning those limits through constant use that eventually delivers excellent image quality for the photographer. Lenses of the same focal range vary in price and it is a rare case indeed when an in-expensive kit lens can out resolve and deliver less imperfections than a professional grade lens. However, I found this interesting -
"Most importantly, even though MTF charts are amazingly sophisticated and descriptive tools — with lots of good science to back them up — ultimately nothing beats simply visually inspecting an image on-screen or in a print. After all, pictures are made to look at, so that's all that really matters at the end of the day. It can often be quite difficult to discern whether an image will look better on another lens based on an MTF, because there's usually many competing factors: contrast, resolution, astigmatism, aperture, distortion, etc. A lens is rarely superior in all of these aspects at the same time. If you cannot tell the different between shots with different lenses used in similar situations, then any MTF discrepancies probably don't matter. Finally, even if one lens's MTF is indeed worse than another's, sharpening and local contrast enhancement can often make this disadvantage imperceptible in a print — as long as the original quality difference isn't too great" more


Subject Distance vs. Resolution
Every lens, even a zoom lens at varying focal lengths has it's established distance limitations for maintaining optimum resolution. For sure the optimum aperture setting plays an important part BUT recognising the distance limitation is paramount. If the primary subject or that distant landscape is pushed too far back and beyond the optimum resolving limit of the focal length used (prime or zooms) then as the print is enlarged the quality of the image may appear mushy. Cropping the image (e.g. a distant eagle in the air to see more of it's head detail) can stretch the quality of the image even further. Most photographers' quickly establish the distance vs. resolution capabilities of a lens and maintain a strict methodology in it's use thereof.


Camera Autofocus System
The camera's autofocus relationship with the lens fitted is paramount. As we move forward with digital sensors which have larger numbers of pixels which are smaller in pixel size, the accuracy of the autofocus required becomes more focused, if you will excuse the pun. Learning the little wrinkles of your camera's autofocus system and also using lenses in manual focus is a continual learning curve, especially if you also use other cameras in your photography.
This is an interesting tutorial about autofocus - "A camera's autofocus system intelligently adjusts the camera lens to obtain focus on the subject, and can mean the difference between a sharp photo and a missed opportunity. Despite a seemingly simple goal—sharpness at the focus point—the inner workings of how a camera focuses are unfortunately not as straightforward. This tutorial aims to improve your photos by introducing how autofocus works—thereby enabling you to both make the most of its assets and avoid its shortcomings"  - read more

Shutter Speed + Image Stabilisation Limits
Shutter speed has to be taken into consideration, especially when photographing moving animals, people and trees waving in the high wind. If you set the shutter speed too slow the image will probably be blurred or at the very least sharp enough in a small print size but blurred in enlargements. However there are occasions when a slower shutter speed can blur a background but capture the moving subject very sharply but this involves panning the camera to match the subject's speed when the shot it taken. Image stabilisation built into a camera body or a lens has shutter speed limitations before a 'hand held' shot will blur the captured image. The photographer has to learn those limitations, especially for 'hand held' night street shots where there is a combination of balancing for 'hand holding the camera and also taking into account the movement of a car, person, animal or even back to waving trees in the high wind in the shot.

Tripod Considerations
A tripod can be used to assist in producing 'optimum' image quality by keeping the camera and lens 'rock steady' but there are technical considerations to take into account. The ability of any camera or lens 'image stabilisation' mechanism to operate when fitted to a tripod, (e.g. IS may required to be switched off) the method of pressing the camera shutter button
, even a hand press can create tripod movement whilst a camera self timer, remote cable or wireless shutter operation are preferable. Some wind conditions might vibrate a tripod enough to spoil the resolution in the image, especially if it is a long exposure and the weight ratio of the tripod in relation to the camera/lens used is wrong because the tripod is too lightweight and not suitable. Most photographers who have a lightweight tripod for hill walking, invariably use a heavy back pack or other heavy object (bag of stones) to tie under and to the tripod to add weight to it, causing the tripod legs to be firmer on the ground.


The Processing Mechanism - Prints - Digital Displays
The 'RAW' image file retains the maximum data to produce the optimum image quality. There are post processing actions that will impact on the final image quality, such as correcting lens distortion which inevitably results in cropping out a section of the image. Other include, cropping (in-camera or PP), correcting lens imperfections, adding software graduated filters, adjusting the exposure and/or texture to parts of the image and conversion to a jpeg image file which compresses and reduces the available image data. Most of this work cannot be seen in reasonably sized prints (tiffs or jpegs) even up to A3 with 16Mpixel digital cameras but could impact on larger print or digital display sizes, especially if there is some HDR software post processing in there. Some camera manufacturers are fully aware of the limitations of their cameras and lenses, especially fixed lens cameras and they will recommend maximum print size limitations to ensure the resolution and image quality is not over stretched. Problems arise when the user (digitally) pixel peeps the image at 100% size which is way beyond the manufacturer's print limitations and expects the same image quality. Viewing distance (digital and print) plays an important role in all of this, stand further back and the display or print can be larger, stand closer and the display or print should be of a size to match the viewing distance.

A 'Raw' file converted to jpeg will reduce the data level, especially if the image is re-sized and reduced in % capacity for the web. When images are re-sized for the web, many photographers forget to re-sharpen them at the time. This often leads them to think that the image is sub standard. Re-sharpening will improve the images but re-sharpening them too much can often lead to artifacts or halos such as compressions as well as
the possibility of jaggies (known as the stair case effect) in non vertical/horizontal lines appearing in certain areas of the web image - in the end it is always about balance in post processing an image for display or print at the correct and expected viewing distance.

Some photographers prefer to use lenses that are designed to soften an image and in many cases there are photographers who produce 'Photo Art' and 'Fine Art' prints, who use post processing to soften and even reduce the amount of material in their images for effect. When post processing a 'RAW' image file some photographers will add a  software graduated filter to the sky to darken it down to put more detail in the clouds, they may even add a colour and it works very well, although in some cases the software (and hardware) graduated filter will not only darken the sky, it also darkens the tops of trees and houses or hills. Many photographers will use a software graduated filter in reverse and apply it with increased exposure (in the filter area of coverage) to a dark foreground to lighten it. Some may even use an adjustment brush to dodge, burn and create different lighting effects but invariably this weakens the enlargement capabilities of the image as very often the adjustment artifacts become more visible in a larger frame size, especially around the adjustment edges. It takes great skill in software to make digital adjustments to images and a great deal of patience to apply the adjustments correctly to produce flawless print enlargements. These days you get what you pay for, so if the software is expensive, there is usually a very good and sound reason.  

Many professional artists use software that can dodge and burn as well as masking and layering the 'RAW' image file -

Check out the Adobe CS Tutorials for more on dodging, burning, masks and layering and for photographers who wish to take post processing to an even higher step, check out Corel Paint and Tablets.





If this article has assisted you in any way - please donate to my Charity of Choice   -   The Sick Kids


Richard Lawrence
United Kingdom


Back to Articles Page