1200mm: Digital Teleconverter

Started 8 months ago | Discussions thread
Eric Nepean
Eric Nepean Veteran Member • Posts: 5,655
Re: Not Interpolation Re: 1200mm: Digital Teleconverter

OutsideTheMatrix wrote:

Eric Nepean wrote:

Note that the Digital Teleconverter function is only for JPEG files, it is not available for RAW files.

There is a reason for that.

Typical JPEG processing discards well over half the image detail.

Building a really good interpolater is an expensive and tricky job. Hard to do and hard to maintain.

It would be downright crazy to throw out much of the image data, and then develop an expensive and tricky interpolation function to bring it back.

IMO what Panasonic and Olympus have done is selected the center portion of the image, and tweaked the JPEG engine to keep much more of the detail.

JPEG typically averages color values are typically average over at least 4 adjacent pixels, simply not averaging will provide the required detail.

In the Luma channel, much of the detailed information is discarded by normalising the DFT results with the quantisation matrix and rounding. Changing the quantization matrix is a straightforward way to keep a lot more detail.

This explains why the DTC is not available in RAW.

But it is only throwing away data that is outside the area of interest and which may not be of any interest to the photographer. I shoot RAW+JPG now (only the JPG file part shows the DTC), why doesn't Oly make the x2 DTC filter available in Work Space so people can apply it to their RAWs? It should work the same way! Also, I sometimes use M size 5 MP for x2 DTC to get a nearly non interpolated result (5 MP vs 4 MP not much different) to get a much faster burst shooting rate, especially with the fully electronic shutter on my EM10Mk2.

But when using x2 DTC at the full 16 MP I do see more crater detail on the moon than I see without the DTC.

The RAW image contains the RGB values of every pixel. This is all the detail that was captured. Some of it is already interpolated, because every pixel is either Red or Green or Blue, and the other two colors are interpolated from adjacent pixels.

No more detail than this can be extracted from the sensor.


You have a G9, which has a 20MP sensor and no lowpass filter. You have mounted a good quality 25mm lens, and it is focussed on a wall 41 feet away.

The vertical field of view is 21 feet 3 inches (6.5m), and the sensor has 3872 pixels in the vertical direction.

Each pixel covers an area 1/16 x 1/16 inch (1.67mm x 1.67mm)

Pasted to the wall is a sheet of paper with two lines of text, printed 1/16th of an inch tall:

Donald Trump will win the USA 2020 election

Donald Trump will lose the USA 2020 election

The camera takes an image.

With 1 pixel per letter height, there is no interpolation software in the world that will bring the information in these lines back. You could just as well have written

Outside the Matrix will be the next US president

However if you add in 4x optical teleconvertor, there will be 4 pixels per per line of text, and 3-4 pixels per character, you should be able to read that.

Building a 2X or 4X Digtial TC  for a RAW image isn't possible.

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