Sensor MP vs resolution

[jetstream]

I'm hoping to get more response here than in the microscopy section, mods please feel free to move if needed.

Looking at some USB microscope cameras some have 5MP sensors another 1.3 MP (but more expensive) and I'm wondering about the relationship between the camera sensor pixel count vs actual resolution as seen on a screen? Does the screen itself play a role?

The 5MP is listed at 1600x1200 pixel array and the 1.3MP at 1280x1024 "resolution".

Any help or direction is greatly appreciated, Gerry

 

Could a mod please make the title sensor not sesnor

Edited November 17, 2019 by jetstream
Title is sensor

[Mr Spock]

Fixed your title - don't know much about microscope sensors though.

Usually sensor resolution depends on pixel size rather than the number of pixels. The smaller and more densely packed they are, the higher the resolution.

[vlaiv]

Not sure what the question is, so I'll just shoot some facts and maybe those will cover your question and give you answer. If not we can expand on that.

1. MP count is related to number of pixels on sensor. 1.3MP stands for roughly 1300000 pixels. 1280 x 1024 - means count of pixels in each row and number of rows. Multiply that two figures and you get total number of pixels. 1280 * 1024 = 1310720 or roughly 1.3MP. On the other hand 1600x1200 is in no way 5MP camera as 1600 * 1200 = 1920000, or 1.9MP camera. For camera to be 5MP you need something like 2500 x 1900 or similar "resolution"

2. Resolution is such a broad term and is used in many contexts - that sometimes leads to confusion. One of usages is related to pixel count of sensor. More pixels on sensor means more "resolution". It is used in similar context for computer screens - larger resolution means more display pixels / dots on the screen (like hd ready resolution is lower than full hd being 1280x720 vs 1920x1080 and that is lower still than 4K resolution - 4096 x 2160).

Another usage of the word of resolution is - how much detail there is in picture in the first place. Blurry image will have low resolution regardless the number of pixels used to represent that image. That can lead to funny construct like: "This low resolution image is recorded in high resolution"   (first usage of resolution is level of detail - second is pixel count).

In astronomy (or specifically astro photography) we have additional meaning of that word (could be related to microscopy as well) - resolution of the telescope / system (how much detail it can potentially reproduce at focal plane) and sampling resolution - which gives ratio of sky angles to pixels on sensor (after projection) - expressed in arc seconds per pixel.

3. Image can be viewed on computer screen in few different ways. One of those ways is 1:1 - or 100% zoom (sometimes referred native resolution - yet another usage of term resolution - btw native resolution can mean something else entirely ). This means that one image pixel corresponds to one screen pixel. Size of the portion of the image that can be shown like this is determined by screen resolution. If you view your image on 1920 x 1080 screen but the image is 1280 x 1024 - it will not take up whole screen. If image is on the other hand something like 3000 x 2000 and viewed 1:1 on 1920 x 1080 - you will only see 1920 x 1080 portion of the image  and you will be able to "pan around".

You can view image on computer screen in "another mode" - something often referred as "screen size". That is the size of the image adjusted so it fits as much of display screen it can. If image is smaller (in resolution - pix count) than screen resolution (again pix count) - it will be enlarged. If it is larger - it will be reduced in size. In any case - display resolution will be equal to screen resolution (both terms resolution mean pixel count).

Hope above is not too confusing and it answers your question.

 

[Alien 13]

I found this information regarding sensor requirements here, I do think there are subtle differences between astro and microscopy cameras due to the latters requirement to take dimensional measurements in some applications. The big plus with microscope optics is that they nearly all follow a strict DIN standard so camera compatibility is easier to get right.

Alan

[jetstream]

3 hours ago, Mr Spock said:

Fixed your title - don't know much about microscope sensors though.

Usually sensor resolution depends on pixel size rather than the number of pixels. The smaller and more densely packed they are, the higher the resolution.

Many thanks Michael.

[jetstream]

1 hour ago, vlaiv said:

Not sure what the question is,

Me neither lol!

I'm trying to figure out a nice USB microscope set up for the 10 yr old grand daughter, who has an interest in science, geology etc and I want to fan the flames with easy,early success and with a touch of "tech".

Thanks much for the info- I was actually wondering about the advertised 5mp and it seemed low on pixels to me, but I know zero about this stuff.

1 hour ago, vlaiv said:

3. Image can be viewed on computer screen in few different ways. One of those ways is 1:1 - or 100% zoom (sometimes referred native resolution - yet another usage of term resolution - btw native resolution can mean something else entirely

Ok, some info says the final "magnification" is dependent on the screen size? how so?

she has a small tablet- can this limit the resolution depending on its own screen pixels?

I have piles of questions actually, including how to automatically stack the images taken at different focus points to produce a razor sharp image across a 3d object... one manufacturer provides a on click stacking function at a deadly expensive price though.

And...lol! and I wonder if the "f ratio" or f stop as in photography plays a role with these cameras in regard to a large portion of the target in "focus". I would imagine but dont know that the f ratio or stop is fixed in these?

Thanks Vlaiv

[jetstream]

1 hour ago, Alien 13 said:

I found this information regarding sensor requirements here, I do think there are subtle differences between astro and microscopy cameras due to the latters requirement to take dimensional measurements in some applications. The big plus with microscope optics is that they nearly all follow a strict DIN standard so camera compatibility is easier to get right.

Alan

Perfect and thanks Alan, you obviously have this stuff figured out- very nice image of the slide in the other thread. Much to read and learn now, great info on Nikons site.

[vlaiv]

Seems that above link has enough info on the topic that I wanted to touch on - mind you, I know next to nothing on how it works with microscopes

I'll just talk about resolution then.

8 minutes ago, jetstream said:

Ok, some info says the final "magnification" is dependent on the screen size? how so?

she has a small tablet- can this limit the resolution depending on its own screen pixels?

In my initial answer I mentioned that there is two ways of seeing image on the screen (there is actually whole ranges in between but those two are significant "points" on this scale) - 1:1 and screen size.

If you view image in "screen size" - then resolved detail and size of objects will be related to two things - size of your screen (and it's pixel count resolution) and size of your sensor - that is physical size. Number of pixels on sensor will not matter as image will be either enlarged or reduced to fit the screen.

"Zoom factor" is therefore function of device screen size. With resolved detail its a bit more complicated and depends on pixel resolution of screen and camera. If camera has less pixel resolution (number of megapixels) then screen - it will be limiting factor, but if it has more - then screen pixel count becomes limiting factor. This is all provided that microscope resolving power is greater or equal to what sensor can record (sampling rate - also mentioned above).

Huh, this is becoming really complicated real fast . I was hoping to explain it in simple terms, but not sure if it can be done. I think we need to approach this from the other end. I'll again make number of points - it's sort of easier for me that way.

1. Target size and sensor size. With telescopes it is about mapping angles on the sky to the sensor - target is at "infinity". With microscope, target is at finite distance - and has some physical size. Sensor has some finite physical size as well. Magnification in this case will be ratio of two things - physical size of target (expressed in mm for example or um) and size of that image on sensor or in focal plane (again expressed in mm, um or whatever units of length). Let's say that you observe object that is 50um in size and you do that with x100 magnification. Image of that object in focal plane will be - 50um * x100 = 5000um = 5mm. It will be 5 millimeters long (diameter, side, whatever dimension we are talking about). If sensor is large enough (some sensors are for example: 7.4mm x 5mm, that would be ZWO ASI178 sensor) it will capture whole image.

2. pixel count of the sensor. Let's imagine that object has it's length 50um and that we observe it at x100 - then, it will cover 5mm on our 7.4mm wide sensor - there is plenty of room.  How many pixels will that image be long? You can answer this question in two ways. First is to use camera pixel count resolution (mega pixels, or rather width x height spec), another is to use pixel size (or sometimes called pixel pitch). Let's use first approach - mentioned ASI178 has 3000 x 2000 pixels - we can use proportion to get how many pixels object will use up: 3000:7.4mm = X : 5mm (sensor x pixel count : sensor width = target pixel count : target width) => X = 3000 * 5 / 7.4 = 2000 pixels wide. Another approach is to use pixel size. This camera has 2.4um pixel size so size of target in pixels will be 5mm / 2.4um = 2083.333

These two differ a bit, so which one is correct. In fact - both are probably slightly off as manufacturers never give you precise sensor size nor pixel size, so in fact this sensor might be 7.3982 mm in width and pixel size could be 2.3925 or something like that - they always round things up, but that is good enough for rough estimation. We can say that image of our object will be 2000 pixels across (give or take).

3. Actual resolution / details in the image. This is very tricky one, and I have no clue how to go about it with microscopes. It is related to sharpness of objective and other things that I know nothing about with microscopes, but it limits how much detail you can have. You can't zoom to infinity and get sharp image - at some point there simply wont be any more detail in image even if you zoom more (same as with telescopes - there is maximum magnification that can be used).

Given link as far as I can tell provides you with some guidelines on this. It will limit pixel size that you should use - any smaller pixel will just make object be larger in pixels (in number of pixels across - see point 2) but image will look blurry.

4. Now that we have our image with certain number of pixels - in our example it is 2000 pixels, we need to look at it on screen. How large will it be? That depends on how you present that image on the screen (viewing application).

Let's say that we use tabled with 1280 x 720 resolution. If you use screen size and put whole image on screen, then object on the screen will take up same relative amount of space as it took up on sensor. Sensor size was 7.4mm and object image was 5mm (or sensor x pixel count was 3000 and object was roughly 2000 pixels) - so it took up 2/3 of sensor width. It will take 2/3 of screen width as well (this is why we call it screen size - sensor image is just mapped to screen so object sizes on image will be relative to size of the screen). Actual object size in pixels will be 1280 x 2/3 = ~853px.

Although you have 6mp camera and you used quite a bit of zoom - you ended up observing object with only 853 pixels in this case.

What if we use the same tablet but our viewing application allows us to use 100% zoom or 1:1 pixel mapping? Then you won't be able to fit whole object onto the screen as it is 2000px across while screen shows only 1280. You will only see a piece of object at one time - and you will be able to pan /scroll around to see all parts of it (but never whole). This is showing you the best "resolution" - or most detail (provided that system could resolve target to that level).

There is range of zooms in between these two points (and actually further out on both sides) - so you can have more zoom out than screen size - image becomes smaller and applications usually fill rest with black frame or similar. You can zoom in more than 100% zoom. Stuff on screen will be larger - but there will be no additional detail, things will get blurry. Best is to keep zoom between 100% and screen size - that way you can see things at best resolution, fit whole object of interest on screen and also observe whole "field of view" (at screen size).

Again, hope that above is understandable.

[vlaiv]

Ah forgot to add.

Depth of focus layering is also used in macro photography with fast lens - maybe look that up online to see if there is any free software that you can use?

Often called focus stacking as well.

Here is what quick search gives on this topic:

https://www.cambridgeincolour.com/tutorials/focus-stacking.htm

Edited November 17, 2019 by vlaiv
forgot to paste link :D

[jetstream]

Many many thanks and now its time for me to learn.

[Alien 13]

58 minutes ago, jetstream said:

Me neither lol!

I'm trying to figure out a nice USB microscope set up for the 10 yr old grand daughter, who has an interest in science, geology etc and I want to fan the flames with easy,early success and with a touch of "tech".

Thanks much for the info- I was actually wondering about the advertised 5mp and it seemed low on pixels to me, but I know zero about this stuff.

Ok, some info says the final "magnification" is dependent on the screen size? how so?

she has a small tablet- can this limit the resolution depending on its own screen pixels?

I have piles of questions actually, including how to automatically stack the images taken at different focus points to produce a razor sharp image across a 3d object... one manufacturer provides a on click stacking function at a deadly expensive price though.

And...lol! and I wonder if the "f ratio" or f stop as in photography plays a role with these cameras in regard to a large portion of the target in "focus". I would imagine but dont know that the f ratio or stop is fixed in these?

Thanks Vlaiv

You mention a tablet there, can it run the required capture software?

Alan

[jetstream]

2 hours ago, Alien 13 said:

You mention a tablet there, can it run the required capture software?

No idea Alan, they are 800 miles away atm and I need to find some more things out. I wonder what requirements are needed to run the programs? The nice thing is there is room to grow in many aspects of this project, but I do want early success.