Fishfinder resolution, definition and screen sizes.

ronje · Post by **ronje** » Mon Dec 23, 2024 8:53 am

FISHFINDER DISPLAYS

This isn’t meant to be definitive (there’s that word) words on fish-finders but it might help some of us explain to Santa what we want for Xmas.

Working out what fishfinder to buy can be a daunting experience if it’s our first purchase. A lot of uncertainty and we rely on advice mostly. Phone a friend.

If we’re upgrading then we already know some of the shortcomings that we want to fix. Screen too small or not enough detail shown plus always a bit apprehensive about the cost. We want to fix the shortcomings at minimum cost.

Think of the similarities between a painting and a fishfinder.

What is it that a painting shows us? It’s a permanent landscape image of a scene frozen in time eg trees, creeks, grass, hills, sky.

The detail contained in the image tells us about the painting (birds, clouds, water) and that fills in the gaps which make up the overall image.

If you have a painting that’s big enough, you can tell what sort of birds. That's the level of detail that most expect from a sounder.

Our fishfinders do a similar thing (an underwater painting) except that they don’t use paint (too messy) AND ‘cos what they display isn’t a permanent image

Fishfinders/sounders use little building blocks of electronic “gizmos” called pixels instead of paint. These pixels (thousands of them imbedded in the back of the screen display) can be individually energized to produce colours on the screen AND to give size.

Its just an image of a scene at a particular instant in time and the image changes as time moves on (along with the boat) so all the pixels need to be energized differently, frequently and simultaneously.

The more frequently that pixels need energizing simultaneously, the more sophisticated the digital processing ability of the fishfinder needs to be.

More pixels also mean greater detail of whatever object the fishfinder can “see” and pass on to the viewer (us) ‘cos it’s the amount of detail that’s important to us.

As we live in an increasingly technological world, surely there are more informed, less confusing ways of referring to detail.

There have been many suggestions ranging from descriptive words with which we all nod in wise agreement (but we don’t really understand). eg resolution, clarity, definition, acuity, sharpness, separation, screen size and pixels - to name a few.

They’ve all been used with abandon but these different words all mean the same thing, don’t they? "You know what I mean even if I’m a bit mixed up in describing it".

No, technically they don’t so any conversation about the subject goes round and round in circles until our heads hurt but nothing has even come close to hitting everybody’s “meaning” bullseye.

The result is that confusion reigns. Just as confusing as the meaning of lure “action”, maybe?

The one word that comes closest and simplest to what we all mean (to me anyway) is detail. Whilst probably not technically correct, it conveys the meaning of what we are referring to.

How much underwater detail does the screen show us? More detail means more “building blocks” (pixels) that are needed and more pixels means bigger screens simply to fit them all on the display.

Having settled on the pixel arrangements (large numbers of them), it’s OK for the screen to be able to display all this detail but we’ve got to be able to see it clearly else its meaningless.

A smaller screen with less pixels means that we sit hunched over with our nose up against the screen just to work out what the display is showing us.

If the sounder, transducer and signal processing can’t deliver the detail to the screen display anyway, then don’t be disappointed if all you can determine is the water depth.

A larger screen means that we can see the detail displayed but from further away.

So there’s an electronic data processing side AND a physical side (eyesight, viewing distance, display size) to seeing detail on a sounder screen.

Here’s an example. The tendency these days is to use a separate sounder while standing up casting eg live image fishing.

How many times have we seen these live image guys standing up yet bent over to see what the screen is displaying?

Bent over because the screen isn’t big enough to see properly from a standing position. Eye strain and sore backs seem inevitable.

For some of us of advancing years, standing up on a casting deck means going for a swim if we get the zigging out of step with the zagging boat motion. In some waters, that’s OK but in other waters that’s not ok ‘cos “something” may try to get us.

Compare sounder screens to television screens. TV screens are big enough to be able to see detail from 3-4 metres away. As a result, we sit further away to watch TV but up close to see detail on a sounder.

Having gotten those physical things worked out, it’s time to look at the display screen pixel arrangements so determine if sufficient “detail” to satisfy our needs is processed and displayed in the first place.

There sure are some large numbers of pixels thrown around there. Big enough to impress the hell out of us.

Numbers like 1024 x 800 pixels per 12inch screen making over 800,000 pixels per screen! A 16 inch screen may have over 2 million pixels.

I guess its also time to get the screen size sorted out as well. Here’s a typical 12 inch sounder.

Screenshot (518).png

Easy peasy? Screen size is measured diagonally in inches.

So how are these pixels arranged? Like so (from ScientiaMobile).

Screenshot (523).png

A 12 inch screen has a lot more pixels per inch (PPI) on the RHS than 10/20 PPI on the LHS.

Even though it’s the same object being displayed on each screen, much more detail of the object is being displayed on the right hand image (125 pixels per inch).

Put a 1inch (25.4mm) postal stamp on the screen and how many pixels are covered?
Also easy peasy. 125 x 125 = 15,625 (and all covered by a postage stamp).

Every sounder tells us how many vertical pixels and horizontal pixels make up the screen. Its easily found on the fishfinder specs in the advertising.

Some maths will tell us the pixel density but we don’t want to do maths. I’ll give you a link to a magic formular calculator if you like but we want to fish.

Meanwhile I’ll just put up a simple data sheet about common screen sizes and pixels that tells us roughly what we want to know.

They make up 2 of the 3 important bits of info with the third being cost.

Don’t try to understand or memorise the following. The lesson to remember is simply that bigger is better.

How can we compare the screen detail on different sounders?

Say screen A is a 13 inch with a pixel count of 1920 wide x 1080 vertical making a total of just over 2 million of the little buggers ( 1920 x 1080) spread evenly across the screen which is 75.6 sq inches in area.

A bit of hocus pocus maths shows that if we paste a 25mm x 25mm (1 inch x 1 inch) postage stamp on the screen, then there are 27,000 pixels covered by that stamp.

27,000 pixels per sq inch ------13 inch screen
……………………………………….

Screen B is a 12 inch with a pixel count of 1280 W and 800 V making a total of 1 million pixels (1280 x 800) spread evenly across the screen which is 65.7 sq inches in area.

More hocus pocus shows that our 25mm x 25mm (1 inch x 1 inch) stamp covers 15,600 pixels.

15,600 pixels per sq inch ----- 12 inch screen
……………………………………

Screen C is a 9 inch with a pixel count of 1024 W and 600 V making a total of 614,000 pixels (1024 X 600) on the screen which is 60 sq inches in area.

We’d be getting a bit tired of licking 1 inch postage stamps by now but if we did it one more time, there’d be 10,240 pixels covered by that stamp.

10,240 pixels per sq inch ------------9 inch screen
………………………………………….

Screenshot (528).png

These figures are mathematical works of art and wonderful but they are simply indicators. That’s all they are.

The real test is how well we can see what the screen is displaying.

I look at it this way.

HD means that we’ll have our nose up close to the screen with 9 inch or under screens and we’ll also be most likely cross-eyed.

With HD 10 and 12- inch models we’ll still have our noses close to screen but probably not X-eyed.

With Full HD models, we can be further away from the screen (probably up to 600mm) before we start to struggle seeing detail.

With UHD models it gets much easier to view detail from a bit further away but…there’s a real price that you pay for that.