Re: A "slanted edge" analysis program

Don wrote: 
On Wed, 28 Sep 2005 02:00:41 +0200, "Lorenzo J. Lucchini"
<ljlbox@xxxxxxxxxx> wrote:


It is customary to use a different weighting than the (R+G+B)/3 average. The ISO suggests the calculation of a luminance channel, so a ratio of approx. 3R:6G:1B is closer to what we experience as luminance.

I suspected this. This is also easy to do, so I'll fix it right now. 

I've only been skimming this thread and not paying too much attention
because the MTF of my scanner is what it is and there's nothing I can
do about it... So, with that in mind...

Well, but I don't plan to stop here. What I'd mostly like to obtain from all this is a way to "sharpen" my scans using a function that is tailored to my scanner's specifics (rather than just "unsharp mask as I see fit").

So, you see, there is a practical application of the measurements I can obtain, it's not just about knowing how poor the scanner's resolution is.

In general, if you're doing measurements it makes much more sense to
use the average. You are *not* measuring your *subjective*
*perception* of the pixels but their *objective values*.

Applying perceptive weighing is counterproductive in this case and
will only skew the results. Or, as I like to say, "corrupt" them! ;o)

I'm not sure. Besides Bart, I think I've read somewhere else that luminance should be used in this process. Perhaps it's even in the ISO recommendations.

And why do you say I'm measuring the "objective values" of the pixels instead of their "perceptual values"? I'm mostly trying to measure resolution, in the form of the MTF. People usually cite the MTF50 and the MTF10, because these are points where it *makes perceptual sense* to measure: MTF10 is about the point where the human eye cannot discern contrast anymore, Bart said.

So you see that I'm *already* doing measurements that are inherently "perceptual". So why not be coherent and keep this in mind throughout the process?

In any case, it makes sense to conform to what other programs of this kind do, so that the results can be easily compared.

Perhaps I can put an option to use plain RGB average instead of luminance. But anyway...

Actually, what I would do is measure each channel *separately*!

.... I'm doing this already.
The "gray" channel is measured *in addition* to the other three channels, and is merely a convenience.

> [snip]

by LjL
ljlbox@xxxxxxxxxx
.

Relevant Pages

  • Re: "near field" speaker measurement
    ... measure latency for the channel connecting to the speaker terminals. ... There is an infinite number of things to do with the frequency measurements so I figured ... of the low pass filter is actually 1/2 the bandwidth of the sweep measurement. ...
    (rec.audio.tech)
  • Re: Kenmore Microwave Oven - 2 failures in 2 years
    ... guide. ... I have seen pictures of guides - a small channel to direct the ... AKA a duct to carry the RF into the oven ... measurements. ...
    (sci.electronics.repair)
  • Re: Kenmore Microwave Oven - 2 failures in 2 years
    ... guide. ... I have seen pictures of guides - a small channel to direct the ... AKA a duct to carry the RF into the oven ... measurements. ...
    (sci.electronics.repair)
  • Re: How bad is that Behringer Crap, anyhow?
    ... IME there is a lot of bad gear that measures good, ... varied either up or down from channel to channel. ... variability of cheap linear pots. ... My hope was that there would be something really bad in the measurements ...
    (rec.audio.pro)
  • Re: A "slanted edge" analysis program
    ... >results of *both* guessing and using measurements. ... I personally don't use any sharpening at all. ... perceive high contrast as sharpness. ... >to "reshape" every color channel based on the positions of the ruler ...
    (comp.periphs.scanners)