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You are here: Home / The Last Word / Sony a7S dark-field images — ISO 100

Sony a7S dark-field images — ISO 100

October 29, 2014 JimK Leave a Comment

In the previous post, I showed plots of data derived from a series of Sony a7S images of the back of a lens cap at various ISO settings. Now I’d like to show some of the filtered images themselves. Since there are 540 images represented in the plots (10 ISOs, 18 kernel sizes, and 3 kernel shapes), I’ll have to be selective. All the images you’ll see in this post have been scaled into the range [0,1],  have had a gamma curve of 2.2 applied (imageGamma = imageLinear^0.45), been res’d down to 640×480, and JPEG’d.

First, the ISO 100 unfiltered image:

a7SISO100-1

What looked pretty awful on the graph doesn’t look bad at all in the flesh.

Here is the ISO 100 image with an 11×1, 1×11, and 11×11 averaging kernel applied:

11 pixel horizontal averaging kernel
11 pixel horizontal averaging kernel
11 pixel vertical averaging kernel
11 pixel vertical averaging kernel
11 pixel square averaging kernel
11 pixel square averaging kernel

Both horizontal and vertical low-frequency variations are visible.

Let’s make the kernel bigger and see what we can see:

107 pixel horixontal averaging kernel
107 pixel horixontal averaging kernel
107 pixel vertical averaging kernel
107 pixel vertical averaging kernel
107 pixel square averaging kernel
107 pixel square averaging kernel

Now let’s look with a really big set of kernels, like those that produced the rise in standard deviations shown in the previous post.

871 pixel horizontal averaging kernel
871 pixel horizontal averaging kernel
871 pixel vertical averaging kernel
871 pixel vertical averaging kernel
871 pixel square averaging kernel
871 pixel square averaging kernel

It’s unusual in modern Sony sensor designs that the vertically-oriented read noise features are visibly more objectionable than the horizontal ones, but we see it here.

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