Pixel density - can the playing field be leveled???

Started Jun 6, 2009 | Discussions thread
Johan Borg Senior Member • Posts: 2,718
Re: The answer of your question is right here

Graystar wrote:
I appreciate the time taken to prepare your samples.

Johan Borg wrote:

Here we go


Since you pointed them out, I will use the still life pictures at
Imaging Resource as an example (there may be better real-world tests,
but it gives us a common ground).

Which ones? You need to start with the RAW files because the Venus
JPEG engine is horrible.

As I said, there may be better examples to use, but from my experience it doesn't matter, the conclusion will be identical if you follow the same process as I outlined. Do it yourself with any input you want if you need a personal confirmation.

What I did with the pictures:
1. First, I resized the G10 picture to the exact same size as the
LX3. According to my theory, this image should now contain inherently
more per-pixel detail than the LX3 picture.

If the images are the same size, then what you have is different
detail, not more. The question is which one is a more accurate
rendition. Also, it has to be kept in mind that the images came from
two completely different cameras. If you compare the mosaic from the
Muscat bottles you’ll see that the G10 mosaic is taller after being
resized. This isn’t a resizing issue...it has to do with the
different lenses. So you have to recognize that when you compare the
Muscat mosaics the G10 image contains more pixels than the LX3 image,
even though you resized the G10 image to match.

I didn't choose the pictures, I used your examples. I didn't choose the cameras, I used your examples. Even then I came to the same conclusion as before

This is always the problem with these types of comparisons...it’s
impossible to create a 100% equivalent transformation. To compare
the two Muscat mosaics by height you have to reduce the G10 image by
0.76723, rather than the 0.8273 that the resolutions difference would
suggest. However, if you do that then the LX3 image is wider. Due
to the different lenses, it’s very difficult to compare the images
and come to any indisputable conclusion. When the resized images are
compared against a crop from the Canon 5D MII, there are areas where
the resized G10 looks a hair more accurate and areas where the LX3
looks a hair more accurate.

I agree that the cameras are very different and therefore complicated to compare. However, this is all irrelevant , since you can confirm this test with a single camera and a single picture. Here is the result if you upsample the 10MP G10 image back up to original size and overlay the original:

As you can see, the loss of detail when going from 14.6 to 10 MP is very similar to the LX3 going from 10 to 6.4MP, and a lot less than when you downsample the G10 image from 10 MP to 6.4 MP.

2. I resized both of them to 80% in each direction, to 2918x2189
pixels, 6.4MP.

Not sure why you did that, but okay.

Turberville mentioned that out-of-camera images lose very little detail when resized to 64% of pixel size, so I decided to use the values we already discussed in the thread.

3. I resized both 6.4MP files up to the original LX3 size again.

Not sure why you did that. Any difference that going to show up
after the resizing acrobatics was there before.

Correct, but I'm not looking for that, I'm looking for whether one of the pictures lost more detail than the other in the process. That would mean that the significance of each pixel in that picture was higher than in the picture where less detail was lost in the process.

4. I copied the original image as a layer on top of the
down-then-up-sampled image and set the blending method to
"Difference", so areas where the sampling had no effect on detail
would be completely black.
5. I cropped both images around an area where they had lost image
detail due to the sampling, the Muscat Wine Vinegar bottle.
Here is the crop from the LX3, showing that there is very little loss
of detail when an image is downsampled to 64% of original size and
then upsampled to original:
Here is the crop from the G10, showing that there is significantly
more loss of detail when you continue to downsample the image from an
already downsampled version:
I don't know whether it's the CFA interpolation or the AA filter that
is responsible, but it certainly seems like a 15MP camera is able to
deliver more detailed 10MP pictures than a 10MP camera.

I’m sorry, I just don’t follow how you come up with that final
conclusion from the previous statements.

The conclusion is: The quantity of information per pixel is significantly higher in the 10 MP picture from a 15 MP sensor and that detail will inevitably be lost in a down-then-up-sample process, as the posted images clearly suggest. What I cannot tell is whether that information is more correct or not, that depends on other parts of the camera, but I can tell that all-other-things-being-equal (which we can agree they never are), a 15 MP camera may deliver more detailed 10 MP pictures than a 10 MP camera.

Comparisons like that mean nothing to me. All you’ve shown is that
something happened. But we have no idea what. I want to see the
images, and I want a control image to show me what’s really supposed
to be there. My own review of the IR RAW files shows that the LX3
native image and the G10 resized image have enough variation from
“true” that I consider them both to be of equivalent image quality.

Now you are comparing various qualities of different cameras, I was only comparing quantity of information per pixel in a 15 MP picture downscaled to 10 MP and a 10 MP original.

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