Estimating fish size

[MuskieBait]

Thought I post this reply up from another forum. Someone claimed to have caught a 31" Smallmouth Bass...while the Ontario record is only 24" long, 18.3" girth and weighing 9.84lbs.

So this person is claiming (not aloud) that his fish is pushing the Ontario record.

Another member did some pixel calculation on his pictures...

rybak Wrote:So ... I took a stab at analyzing the photo by using some common human anatomy measurements like the average width of eye and length of an ear to come up with the following:

eye: 15/32" to 15/16"
ear: 2.52"

In pixels on the photo:

ear: 80
visible eye: 30
fish: 840

fish to ear ratio- 1: 10.5
fish to eye ratio- 1: 28

According to average ear length the fish is: 26.46"
According to average visible eye width the fish is: 26.25"

So, my crackpot science sort of confirms that the fish was a BEAST! nice catch.

The folly in that estimation...the issue of perspective is not considered. In pictures, objects closer to the camera appears bigger (I don't need to tell you that)...so even though the fish was estimated at 26" in 2D, it really isn't 26" in real life.

So I took on the challenge...

Certain common objects can offer some estimate of the fish...regardless of how big or small the person in the picture may be. People often claim they are such and such height and weight and grossly overestimate fish size. I just had to look at the size of the ball cap visor and say BS because an unbent ball cap visor is usually 7"-7.5" wide. When bent, it ranges from 5.5"-6.5" wide...depending on the size of the "roof top".

Otherwise...to prove a point...I set this experiment up...

2 American pennies (Don't have Canadian pennies anymore [] ) set on a piano bench exactly (measured) 12" away from each other in "depth", and 1" slightly offset with each other laterally.

First picture was taken with the camera lens set exactly (measured) 22" above ground, and exactly (measured) 12" away from the closer penny (and exactly 24" from the further penny). This is a fairly unrealistic situation where the object (fish and angler) is so close to the lens...but use here to illustrate a point.



In this case, the closer penny is 191 pixels in diameter, while the further penny is 101 pixels in diameter. If we use the further penny as comparison for "actual size", then the penny that is closer is enlarged 89%...it almost doubles in size! I don't really need to tell you that. You can probably see that the penny that is further away is 1/2 the size.

OK...let's bring the camera back from the pennies.

Second picture was taken with the camera lens set at the same height (22"), and exactly 36" away from the closer penny (and exactly 48" from the further penny).



In this case, the closer penny is 68 pixels in diameter, while the further penny is 51 pixels in diameter. Again, using the further penny as comparison for "actual size", the penny that is closer is enlarged 33%! Again, I don't need to tell you that the penny that is further away is about 3/4 of the size.

So...as you can see, the enlargement factor is quite severe. I don't think I need to tell anyone that holding a fish closer to the lens makes the fish look bigger...but I don't know if people are aware just how much "bigger" the fish looks.

The further you set apart the pennies, the bigger the discrepency in size. I love how people always mention how big they are in the picture. If you claim you are taller and wider in built, it also implies your arms are longer and the fish is held out further...which means the actual size of the fish is actually smaller than it appears. It works against you...not for you.

But still, rybak's estimation has merits. If we take my measurements and enlargement ratios to what rybak has measuered, assuming that the photographer was 36" away from the fish and the fish was held out a reasonable 12" from the face (which I'm being generous...because with arms from a 6'1" body it is more than 12"...after all, a ball cap brim is about 5" long)...then you have an enlargement ratio of 33%...or flip it around we should shrink the fish to 75% of the apparent size...

That means the fish is 19.8" (round up)...Which is what I estimated without doing all that silly photography and calculation anyways.

Again, I'm being generous here assuming that the fish was ONLY held out 12" from the face.

All that to say...the smallies looks to be 4-5lb fish...and people should not overestimate an Ontario record breaking fish length without a tape measure...because that estimation certianly looks fishy. A 31" smallie it isn't unless you can show some pictures of the fish beside a tape.

BTW, if you really claimed the smallie is 31" long, then your forearm must be 24" long. You must be an orangutan...

[OldTimer]

Hey MB - Guess that would be your two cents worth huh?......................smile

Admit it.......... you expected this comeback..........grin.

Also note that your calcs are a bit off..............American pennies are presently 8% larger than Canadian.

Cheers,

OldTimer

[MuskieBait]

That makes a lot of cents, OT.

Wise guy...I should put this on my blog and name it "My two cents on fish photography" Thanks for the inspiration.

[MichaelAngelo]

(08-13-2014 04:01 PM)MuskieBait Wrote:  That makes a lot of cents, OT.

Wise guy...I should put this on my blog and name it "My two cents on fish photography" Thanks for the inspiration.

LOL not bad! Definitely get that posted

[OldTimer]

Or use $1 bills to see if you can buck the theory............... bada..boom

[Dave Bailey]

Caught a 22" smallmouth up in Killarney PP last week, measured it with a tape, but from looking at the video there's really no way to tell the size accurately. I wouldn't trust any measurements made from a picture or video.