Can anyone resolve a resolution problem I have?

[bobt]

Hi,

I may well have asked this before, but if so I either have forgotten or don't remember the answer. If so, my apologies.

I have a mental block about resolution.

As I understand it, resolution is essentially the density of pixels per square whatever. Therefore if a square inch contains 500,000 pixels it will be much clearer and sharper (i.e. higher resolution) than a similar square containing only 250,000 pixels.

Now ... if that is correct, what happens in the following scenario. I photograph a chess board at two different resolutions. I process them both on the PC and on the lower resolution image I cut out one of the squares. I copy a square from the higher resolution image and place it in the place of the removed square and then merge that image into one. What happens to that image? Does it have 63 squares all with 250,000 pixels - plus one square with 500,000 pixels? If not, why not?

Yours sincerely,

Confused.

[jjnic]

You answered your own question :-) The insert is merged into the image so it will have the same pixel density as the rest of the image. You can't have an image with 2 different pixel densities
jj

[arthurking83]

Well. technically I believe you can have two different resolutions for the one file.
The caveat will be tho, that the display of the image will need to be set to a minimum resolution of the higher resolution section of the image to be worth the effort.

That is, if the highest res section of the image is set to 500K ppi the image needs to be set so that this resolution is the minimum for it to display the detail in that square.
The rest of the image will be a mush detail tho of course .. so why you would do this is a questionable excersize.
So only the one square will display any detail, the other 63 squares will display fuzzy blobs of either splotches of ink(if printed) or light(if displayed on a screen).

If you normalise the entire image to be viewed in a commonly acceptable human friendly format, then as jjnic implied .. the lowering of pixel density will affect the display of the higher res square.


ps. you should try to limit your resolution values to about 70-100 or so pixels per whatsit (including inches)!
pps. for printing 200-300dpi is an acceptable standard


** For a rough estimate of ppi(screen) and dpi(print) values:
A good screen will have approximately 70-100(ish) pixels per inch.
This is not usually stated in sq inch values. For sq inch resolutions values, square the value of the screen resolution.

So if your screen has a 72 ppi resolution value, the it's sq inch value will be 72² (5184) .. etc, etc.

A high quality print will have been printed to 300dpi .. and if a larger size print is required, 200dpi can be acceptable with generally good results, but depending on the fineness of the detail within the image.

[jjphoto]

...

Now ... if that is correct, what happens in the following scenario. I photograph a chess board at two different resolutions. I process them both on the PC and on the lower resolution image I cut out one of the squares. I copy a square from the higher resolution image and place it in the place of the removed square and then merge that image into one. What happens to that image? Does it have 63 squares all with 250,000 pixels - plus one square with 500,000 pixels? If not, why not?

Yours sincerely,

Confused.

JJ answered your question. The larger image will have to be reduced in size to fit the smaller image.

BUT...

Hi,

I may well have asked this before, but if so I either have forgotten or don't remember the answer. If so, my apologies.

I have a mental block about resolution.

As I understand it, resolution is essentially the density of pixels per square whatever. Therefore if a square inch contains 500,000 pixels it will be much clearer and sharper (i.e. higher resolution) than a similar square containing only 250,000 pixels.
....

People often use 'resolution' and 'sharpness' interchangeably but they mean different things. You could have just two pixels, one black and the other white and their 'sharpness', 'definition', or 'acutance' would be as high as possible but with extremely little resolution (two bits of information). Conversely if you had lots and lots of pixels of information and all of them where very low contrast then even though they may have immense resolution (lots of information) they would still not look sharp.

Sharpness = Resolution x Contrast

But I digress...

[bobt]

Hmmmm .. thanks guys. This may well be one of those things that never penetrates! I guess I'll have to do some serious experimentation to see what happens when I copy and paste different layers. It's still a little clear like mud.

[nimrodisease]

FWIW, in real world you would almost never have 500,000 pixels per inch (PPI). A more common figure would be 300.

I don't really understand why anyone would want to do what you have suggested in your first post, so it seems somewhat irrelevant to me. I'm really not sure what is the heart of the issue that you're trying to understand.

I think a more sensible way of looking at it is in terms of dimensions. That is, if you compare a high-resolution image (say 3000x2000) to a low-resolution image (say 900x600), then (assuming all other factors are equal) you will be able to get a larger/higher quality print out of the image and/or display it well on larger monitors. Beyond this, I don't quite see what the relevance is.

[arthurking83]

FWIW, in real world you would almost never have 500,000 pixels per inch (PPI). A more common figure would be 300.

......

The often quoted 300dpi(for printing purposes) is quoted for each length of an inch.
For the value of 500000 pixels(or dots or whatever) as stated by Bob, you would use the square root of this figure (he's used a value of 500000 per sq inch).

I think that equates to about 700 anyhow .. which is massively over the top too anyhow.

While it would be more normal to think of Bob's question as only a curiosity, and not really applicable to a real world situation, it doesn't necessarily mean that the question is not applicable in the real world!

You could easily imagine a high profile photographer in the process of printing a massive 10 meter wide mural, which would normally be printed at a low resolution value ... more so for cost purposes than anything else. But the low res print output, usually at about 72dpi or so for massive poster sizes, is done so more because of the viewing distance. At say 5 or so meters viewing distance, 72dpi would still give quite good image detail to the viewer looking at the image as a whole.
But this high profile photographer may also want folks to walk up closer and examine some hidden detail amongst the wide aspect of the mural, and may then want to print some areas at a much higher resolution.

If the image is created large enough, then there would be no reason for the resolution scenario that Bob's question pertains too doesn't hold true. You should in theory have the ability to view an image at multiple resolutions, as long as the finest resolution is actually something that can be seen by the human eye. If the human eye can't discern those fine details, then having them there is wasted data.

I don't have CS as an image editing option so I can't confirm this, but an easy test to see if multiple resolutions within the one image is possible is (or should be quite easy to do, even on an image that is within the realm of sanity.

Take any image and downsize it to something small .. the downsized image should be 600x400 or something very small. Then with this downsized image, use CS to upsize it(say 3000x2000 so that the resolution of this image turns the details into a mushy mess.
Then using a part of the original image again, crop out a section and overlay a small high resolution portion back over the upscaled mushy version fitting nicely where its supposed too.
I don't have ready access to any software with the ability to layer images in this manner.

I would have to think that creating an image in this manner should allow for Bob's hypothetical question to work to a certain degree.
Why someone would want to create an image in this manner .. well why do people shoot with LoFi cameras, or still use antiquated processes for their photography .... etc, etc.

One example of how I can see this question having been used(already) is in those mosaic images where you keep zooming in onto a murky yet understandable image, and each time you zoom in, you see a smaller image of something else that is also discernible.
This was quite regularly done a few years back when it was an interesting idea, where an image of a person as a whole was made up of smaller images of other people as you zoomed in. And the more you zoomed in, the more detail was seen of other people making up the image of the person you just zoomed into.
The last one of these types of endless zooms was one of a series of faces making up an image of the Earth.

Earth waves at Cassini
This one only has the one layer of zoom, but I've seen other images with more layers of zoomability.

[nimrodisease]

I do agree with everything you've said Arthur. But, it is still a very obscure kind of thing to be asking about, and I'm still not really quite sure what the misunderstanding was in the first place.

Perhaps the original question was more concerned with potentially confusing terminology (PPI, DPI, pixels, resolution, etc) and we're thinking too much about it..?

[bobt]

Perhaps the original question was more concerned with potentially confusing terminology (PPI, DPI, pixels, resolution, etc) and we're thinking too much about it..?

Thanks for all those answers ...... I think I'm just trying to establish in my own mind the mechanics (or physics) of what actually happens - and although I'm talking in terms of pixels I am imagining the whole thing in a very physical way rather than in a digital way. Therefore, if I were to use pieces of paper rather than digital images I could have one chessboard constructed of squares containing 500 dots each (the number is irrelevant really) and I could then stick a single square on top of one square which would perhaps have only 50 dots. Physically, that's certainly possible, and from a distance the square with 50 would look entirely different to the other squares.

I'm just not sure why that doesn't happen if you use layers of dots (or pixels) - somehow those different squares no longer have differing numbers of dots.

I'm probably missing something obvious - but that's my understanding of pixels and dots anyway.

[swifty]

I'm not so sure your first assumption is correct.
The resolution should be the total pixel count (ie. no. pixels length X no. pixels width).
You can then display that total resolution at various densities depending on your display medium.

On a given monitor, this density is fixed (its a physical specification of the hardware). Essentially when you display a photo at 100%, you're displaying one photo pixel per display pixel.
So in your chessboard example, with both the low resolution file and high resolution file displayed at the same magnification percentage (lets say 100%), the high resolution square will not fit on your low resolution cut out. So you couldn't combine the two in a way such that the high resolution square fits the low resolution chess board cut out exactly (it will be bigger).
To do so, you'd upsized the lower resolution chessboard file to a size where the chessboard cut out now equals the higher resolution square. Now you could combine the files such that the square fits the cut out exactly. But you've only done so by upsizing that low resolution file to a high one.

If you did the above with a subject with lots of detail (not a chessboard unless the chessboard had lots of fine wood grain or something). Lets say a portrait of a person, one in low resolution, and one at high resolution but otherwise identical. Then you just cut out the eye on the high resolution file, upsized the low resolution portrait to the resolution of the high resolution file such that the eye from the high resolution file will now fit correctly and combine it. You'd now end up a file equal to the high resolution file but lacking in detail everywhere except for the eye where you've substituted with the high resolution image.

That's my understanding of it anyways. I was going to go into 'arc minute' resolution which is more relevant when talking about viewing distance but I think that may confuse even further.