Spectrum Images

[mechman]

This will be a thread solely for spectrum images. I know that they're handy for some folks (Smokey ) and I'd like to keep them here for all to see and use if needed. Some of them are different formats as they were done using iMatch Software and exported to Excel where the graph was made. They make for much nicer looking graphs but unfortunately there is the possibility of someone accusing me of 'tampering with the numbers'. That's why I always have BabelColor images as well. I know of no way that I could tamper with those numbers.

Black Widow - AAA/Bermuda Beige


Auto Air Aluminum Fine


Black Widow - AAA/Bermuda Beige


Black Widow Trial using Essential Gray as the base


True Value Winter Mist


The HE558 compilations of Black Widow


HE558 on its own


True Value Winter Mountain with a Folk Art Pearlizing medium topcoat


True Value Winter Mountain


True Value Winter Mist with pearlizing medium topcoat


another of True Value Winter Mist


Behr Ultra Pure White 1050


My WhiBal card


mech

[mechman]

Sherwin Williams Soothing White


Behr Silver Screen


Wilsonart Platinum


CMRA's S-I-L-V-E-R


MississippiMan's Silver Fire


Same but from Harp and zductive


Kilz2 primer


Sherwin Williams Gray Screen


Wilsonart Designer White


CGiv


mech

[Harpmaker]

I'll be happy to add my charts to the thread as well.

I think folks should know how to read these things. For example, your chart of "Auto Air Aluminum Fine" just about gave cynical2 a heart-attack until he saw the scale it was drawn to!

The horizontal X-axis represents the colors of the spectrum the spectrophotometer measures. In my case, my spectro measures from 400nm to 700nm; mech's spectro goes from 380nm to 720 or 730nm. Ultraviolet light begins at 400nm and Infrared begins at 700nm, so mech's spectro can measure further into the Ultraviolet and Infrared spectra than mine can. Oh yeah, nm = nanometers, the frequency of the color.

The vertical Y-Axis represents the reflectivity value of each color and is where things can be misunderstood. In mech's "Auto Air Aluminum Fine" chart, the line doesn't look flat at all! It looks like it slopes steeply from the blue end of the spectrum to the red end; but if you look at the scale of the Y-Axis you will see that it only goes from 0.29 to 0.37 (from 29% to 37% reflectivity). Below is a chart of the same type of paint I made with my spectro that looks quite different, but if you look at the scale you will see the measurements are almost identical; the difference is my chart uses a Y-Axis scale of 0 to 100%. The smaller the values represented by the Y-Axis, the greater the color differences of the paint will be magnified on the chart.

[mechman]

Thanks Harp!

mech

[thxgoon]

Sorry if this is a total noob question but are the values of reflectance the same thing as screen 'gain'? In other words could you infer from your graph of the Black Widow that it has a gain of .5 (give or take)? Thanks.

[wbassett]

No you can't get gain from these charts. Their purpose is to show the spectral reflectance 'curve'. The flatter the line the better and it will reflect light back equally throughout the visible spectrum.

[thxgoon]

wbassett wrote:

No you can't get gain from these charts. Their purpose is to show the spectral reflectance 'curve'. The flatter the line the better and it will reflect light back equally throughout the visible spectrum.

That makes sense, I just read the thread where you explained in detail what gain is. Thanks! So what would be the difference between a flat curve at .5 and a flat curve at .8?

[Harpmaker]

thxgoon wrote:

That makes sense, I just read the thread where you explained in detail what gain is. Thanks! So what would be the difference between a flat curve at .5 and a flat curve at .8?

A Spectral Curve reading of .5 indicates the paint, or whatever is being measured, has a reflectance of 50 percent. A reading of .8 would be 80 percent. 0 percent is total black and 100 percent would be total white.

The reason one cannot interpret these reflective values as screen gain is the specto intentionally projects a measured color and intensity of light from three different angles so as NOT to get a "gain" (or specular reflective) reading, but rather a true value of the brightness/lightness of the paint regardless of it's flatness or glossiness.

When one measures screen gain, what they are measuring is the screens reflectance in a very narrow cone with the single light source not changing position; first at 90 degrees (face-on toward the screen) and then from other angles moving away from 90 degrees. If the reflective value of the screen decreases as the viewer angle changes, the screen has "gain". Generally, the higher the screen gain, the greater/faster the reflective difference changes as the viewing angle is moved away from 90 degrees.

In some cases the exact same spectrophotometer can take both spectral curve readings and gain readings (mine can't). The difference is in how they are taken; and one really has nothing to do with the other even though both are reflective readings.

The other way a screen can be said to have gain is to compare it's reflectance value to a block of magnesium carbonate (which is very white and has a gain of 1). A flat dark gray screen will have have less "gain" than a flat light gray screen, which will have less gain than a flat white screen.

As you can see, things can get very confusing very fast when discussing gain.

I don't know if I've answered any questions or just muddied the waters. I probably should have kept quiet and let wbassett answer.

[thxgoon]

Harpmaker wrote:

I don't know if I've answered any questions or just muddied the waters. I probably should have kept quiet and let wbassett answer.

That makes perfect sense. Thank you!

[mechman]

I was planning on chiming in here but it appears Harp has answered your question. and very well I might add!

mech