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UltravioletPhotography

UV & IR Channel Recording Comparison


Andrea B.

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Experiment: Take a typical UV and IR foto and compare the channels to see where UV and IR light is being recorded by a typical converted digital camera.

Rather broadly defined, yes. But it will be fun to look at.

 

Result: In both UV and IR fotos, light is recorded in all three channels.

 

Please comment and do point out errors!! I have no embarassment about screw-ups and am happy to make corrections. If I don't try, I don't learn. [Anyone embarassed about screw-ups should not be making experiments before the well-educated UVP readers!]

 

 

Equipment: Nikon D600-broadband + Coastal Optics 60/4.0 + Sunlight

 

REFERENCE FOTOS: As shot with my usual in-camera WB settings which are for convenience. No conversion, no profiling, just Jpg extraction shown in these Ref fotos.

 

Visible Reference: Baader UV/IR-Cut Filter

f/8 for 1/1000" @ ISO-100

My in-camera convenience WB setting for Visible work is fairly accurate.

testFilter_vis_sun_20160205wf_4237602.jpg

 

Infrared Reference: B+W093 IR-Pass Filter (830nm)

f/8 for 1/200" @ ISO-100

The preceding Visible setting was used for the IR (which is monochrome).

testFilter_093IR_sun_20160205wf_42380.jpg

 

Ultraviolet Reference: BaaderU UV-Pass Filter

f/8 for 1/15" @ ISO-100

My in-camera convenience WB for UV work is used because it is as close the actual raw composite as I can push a Nikon in-camera white balance (at this time).

testFilter_baadU_sun_20160205wf_4238801.jpg

 

 

 

RAW COMPOSITES:

Here is what was really recorded as seen by Raw Digger after demosaic, gamma curve and end-point balance (which are required to make the raw suitable for human eyes). Minor alterations have occured due to resizing and stuffing into an sRGB Jpg box. Raw Composites look dull. NO white balance has been applied.

 

Visible Raw Composite:

There is 1% underexposure in the Red channel, .5% underexposure in the Green channels,

and 3.3% underexposure in the Blue channel.

testFilter_vis_sun_20160205wf_42376_nef.jpg

 

Infrared Raw Composite:

There is no under-exposure or over-exposure.

testFilter_093IR_sun_20160205wf_42380_nef.jpg

 

Ultraviolet Raw Composite:

There is 12.7% underexposure in the Blue channel and 1.3% underexposure in the Green channel.

The Red channel has come close to overexposure.

testFilter_baadU_sun_20160205wf_42388_nef.jpg

 

 

 

CHANNEL HISTOGRAMS:

The x-axis shows EV in increments of 1/3. The y-axis count is linear. The overall range is based on the D600. Channels seem to oversaturate around EV+3.

 

The histograms for the entire photo do not seem particularly interesting to me. After this I'll take some samples so we can better compare how UV and IR are recorded.

 

Visible Channel Histogram:

testFilter_vis_sun_20160205wf_42376-Full-6034x4028.jpg

 

Infrared Channel Histogram:

As per the way I have RawDigger set to Auto-analyze over- & under-exposure, this shot is neither. Still in the real world I think I could have let in a little more light.

testFilter_093IR_sun_20160205wf_42378-Full-6034x4028.jpg

 

Ultraviolet Channel Histogram:

testFilter_baadU_sun_20160205wf_42388-Full-6034x4028.jpg

 

 

SKY SAMPLES:

Now, to me, things get interesting when you look at sampled portions of the photographs.

I took a small squarish sample from the sky in the upper left corner so I could compare the UV and IR recordings.

In UV light, skies go bright. In IR light, skies go dark.

So we should expect to see this in the sample histograms.

 

The sky samples are shown as a raw composite with no white balance applied.

 

Visible Sky & Histogram

The Visible sky is recorded as raw cyan with blue leading just a bit.

The EV between 0 and 1 is between the IR and UV values which follow.

Screen Shot 2016-02-05 at 5.08.01 PM.jpg

testFilter_vis_sun_20160205wf_42376-Sel-763-127-133x86sky.jpg

 

Infrared Sky & Histogram

The IR sky is recorded as basically monochrome and darkish around EV -3.

Red and blue lead just a bit over raw green.

Screen Shot 2016-02-05 at 4.49.23 PM.jpg

testFilter_093IR_sun_20160205wf_42380-Sel-767-133-133x86sky.jpg

 

Ultraviolet Sky & Histogram

The UV sky is recorded as bright orange-red around EV +2.

The large amounts of blue & green desaturate the raw red.

Green leads blue to give the orange push.

Screen Shot 2016-02-05 at 4.50.19 PM.jpg

testFilter_baadU_sun_20160205wf_42388-Sel-763-127-133x86sky.jpg

 

 

SHRUB SAMPLES:

This comparative sample is taken from the evergreen Euonymous shrub.

In a manner opposite to the sky, in UV leaves go dark. In IR, leaves go light.

Again, we should see this in the sample histograms.

 

The sky samples are shown as a raw composite with no white balance applied.

 

Visible Shrub & Histogram

The Visible leaves are dark brownish-green around EV -2.

Screen Shot 2016-02-05 at 7.42.25 PM.jpg

testFilter_vis_sun_20160205wf_42376bush.jpg

 

Infrared Shrub & Histogram

The IR leaves are monochrome and moderately bright in winter light at EV +1.

Screen Shot 2016-02-05 at 7.37.23 PM.jpg

testFilter_093IR_sun_20160205wf_42378bush.jpg

 

Ultraviolet Shrub & Histogram

The UV leaves are very dark red around EV -2.5.

Screen Shot 2016-02-05 at 7.39.37 PM.jpg

testFilter_baadU_sun_20160205wf_42388bush.jpg

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So what would the three original fotos look like if converted & edited?

Just test scenes, so nothing much to write home about. :)

 

testFilter_vis_sun_20160205wf_42376pn.jpg

 

 

There is a woodpecker in this foto.

testFilter_093IR_sun_20160205wf_42380pn.jpg

 

 

This one too.

testFilter_baadU_sun_20160205wf_42388pn.jpg

 

 

Unresized excerpts 2/3 of which contain a Downy Woodpecker.

Vis/IR/UV

testFilter_vis_sun_20160205wf_42376pn01.jpg testFilter_093IR_sun_20160205wf_42380pn01.jpg testFilter_baadU_sun_20160205wf_42388pn02.jpg

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