Why is the SNES' or SFC's video output blurry?  I don't know!!  But for how and where it is smeared and blurry, read on as I run a technical diagnosis and explanation of the (RGB) video output of 2 generations of Super Famicom hardware.

1. MEASUREMENTS  |  2. EXAMPLES & EXPLANATION  |  3. GAME SCREENSHOTS

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1. MEASUREMENTS
 
OLD SFC / SNES
SFC Jr.

I connected the probes of my oscilloscope directly to the multi-AV-out connector on the rear of the two different Super Famicom models, and measured their signals.

The test images that I used had a single 8-pixel-wide bar, on a solid background. I tested all combinations of white, black, and grey bar/background.

As these images should show, on the old model SFC/SNES, pixels have a slightly longer (slower) rise and fall time overall compared to the SFC Jr (resulting in slight blurring).  However, for a rise/fall between zero <-> 100% in each RGB colour component, the old model SFC is not unreasonably bad compared to the SFC Jr.

This is unwanted, but it is not the main problem.

The biggest problem is apparent for a voltage rise or fall to a pixel of intermediary value (medium grey, orange, purple, etc.): The old model SFC has a very long rise and fall time to this level.

When going from a black background to a medium grey, the rise on the old SFC takes about 0.6 microseconds, making the left side of this transition extremely blurry.  The right side is still reasonably sharp.

This happens for any of the colour components independently, so a rise from black to bright red will be sharp, but from red to orange (as it has 50% green) will have the left side of the transition blurred on the old SFC/SNES.

The fall time on the old model SFC is similarly sluggish when going from extreme brightness to an intermediate value.

The result of this long fall time is a blurry right edge of graphics in this case.
The following sets of pictures go on to show the problem on the 1st-generation SFC / SNES: any transition towards black or white (etc) is sharp enough, but any transition towards grey or another muted colour results in a slow change towards that colour.
 
 
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2. EXAMPLES WITH COLOUR CHANNEL EXPLANATION

For a token example with screenshots from an actual game, see below, but I think SNES/SFC blurring is easier to spot using a controlled demonstration of different colours of text on coloured backgrounds.  Perhaps you too may have seen some SNES games where the choice of text and background colours was soo poor that it made the text harder to read...

In these examples, I displayed the text on my two SFC models, and took simple photographs of my RGB CRT monitor.  I'm sorry for their crudity. Oh well.
BITMAP
SFC Jr.
Old SFC / SNES

On the 1st-model Super Famicom, a colour transition from orange to red causes no additional blurriness, but one from red to orange does.

Hence, the right sides of the red text above are blurred on the old SFC, making the text look fatter.  Conversely, the red background blurs into the left side of the orange text, making the text appear thinner on the old SFC.

BITMAP
SFC Jr.
Old SFC / SNES

Here I made a purple background (both red & blue at medium levels) with cyan-tinged blue text.  Since the green component increases to a mid-level when going from purple, the left side of the text is smeared on the old SFC.  And since both the red & blue components converge to a mid-level when going towards purple again, the right side of the text is also smeared.


BITMAP
SFC Jr.
Old SFC / SNES

Finally, here is an example where the first-model SFC / SNES performs equally well as the SFC Jr. / SNES Jr.  Transitions from one primary colour to another (or to black) cause no colour smearing as the components settle into their extreme low or high values.

The only artifacts to be seen are the phosphor alignments clashing on my CRT monitor during the transitions.  Sorry about that. :-)
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3. SCREENSHOTS
 
SFC Jr.
OLD SFC / SNES
These are just a couple of quick photographs from my CRT screen of each SFC model through RGB.  Some more detailed close-ups are below.
Note how from the black outlines of Goemon's head, his face gradually fades in from the left on the old SFC.  The blue hair at the top of his head is also indistinct.  The SFC Jr. has clearer definitions here and in the gradation on the grey bell.
Blurring between the blades of grass and indistinct tones on the grey stone are of note here.

Finally on the title screen, the right-hand edges of any white pixels, and the left-hand edge of the blue sign blur quite strongly.  Bah.

 

 

Thanks for reading!

 

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