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Tutorial - Do high megapixel cameras produce softer images ?

As cameras get increasingly more pixels packed onto their sensors one would hope that provided the manufacturer has controlled adverse qualities such as noise, the increased resolution will bring image quality improvements with each generation of camera.

However, several people I have spoken to feel that the latest cameras produce softer images and are more vulnerable to camera shake than their forebears.

Canon have produced an article on this topic here: Capturing the image : Pixels and image size/ quality. In it they say "Recent models have more pixels, which means that pixel size is smaller. Smaller pixels are more sensitive to camera shake, as a smaller movement will cause the image to move across more pixels."

It is important to view your images at full 100% resolution on the computer when assessing them, so could the image softness simply be due to our inspecting images at larger and larger sizes ? Let's take a look:

Uncropped starting image from the mkIV (reproduced here at 590x393 pixels)



100% crop of the 16 Mp 1DmkIV image (4896x3264)



Next, I have used photoshop's bicubic interpolation to reduce the size of the MKIV image down to mkIII size (10.1Mp). All images have been sharpened lightly and identically throughout. Does the image look sharper ?

100% crop of original image interpolated down to 10.1Mp 1DmkIII size (3888 x 2592)



Next the original image was simlarly reduced again to 1DmkII size(8.2 Mp). Is this sharper still ? I think it does, do you ?

100% crop of original image interpolated down to 8.2 Mp 1DmkII size (3504 x 2336)



Results

Despite undergoing (destructive) bicubic interpolation, the crops appear to get sharper as the image size decreases.The first 16Mp mkIV image does indeed look quite a bit softer than the last mkII sized image. However, as the images are all just resized from the one master image, we can only be looking at the consequences of image size rather than softness due to a camera megapixel issue.

Conclusions

When we inspect the high Mp images at 100% we are looking at a much smaller part of the image magnified on our screens. We are therefore looking a good deal more critically and can expect to see defects much more clearly - such things as camera shake, motion blur, mirror slap, lens quality shortcomings will all be amplified. If you want to inspect your images warts and all at maximum size, you need to carry on viewing at 100%, but if you want to see your images looking as good as they used to in the past you may have to start viewing them at a smaller size.

If you print out an image from the 16Mp camera and compare it to an 8Mp camera using the same lens, focal length, and aperture, sharpness will be be the same at all sizes but the higher pixel count camera will print larger due to higher resolution.

To satisfy yourself that your new 21Mp camera is not worse than your old 10Mp one, try viewing it at 50% on the screen or to see it looking really good, try this:

Take a good image and view at 100% (Actual pixels). Then Image> Image size >Ensure all the three boxes are ticked and then change the width to 1000 pixels and select Bicubic sharper
from the drop down menu at the bottom of the dialogue box. Click Ok. Finally sharpen the image
to taste and you will then see just how awesome your image can look on screen.