multispectral cucumbers

[Fandyus]

I have been taking a lot of photos lately. This time I decided to investigate a pair of cucumbers. I illuminated them with a halogen spotlight, which emits enough light for IR, visible and UV.

IR tri color is using my GRB3 method

UV is taken with a ZWB2+QB39 stack (which surprisingly does not leak significantly, even with halogen)

I will also be including the individual pictures if anyone else wanted to take a shot at processing them (please, do post). I'd especially appreciate if someone managed to stack all 7 channels continually. I only could stack them by binning the visible and the IR part of the spectrum together.

The pictures are in full hd so if you still have a 1080p display, you might want to enlarge.

 

visible

 

IR tri color

 

850nm+720nm+red

 

Aerochrome simulation

 

GBUV

 

full spectrum

 

 

individual color channels:

 

950nm longpass

 

~850nm band

 

~720nm band

 

red band

 

green band

 

blue band

 

UV band (400-350nm)

 

 

I also decided to stack the images in Photoshop and pick the range stack mode, I got interesting results.

All of the bands stacked:

 

All of the bands except for UV stacked:

 

IR only stacked:

 

IR only stacked (normalized):

 

Bonus: IR stacked, normalized and processed with Topaz Denoise AI:

 

Here's the IR range mapped on the visible image:

 

Here's the range between 720 and 850 bands mapped on the visible image:

[Fedia]

The GBUV looks delicious ! It has the color of a nectarine.

 

A question though, why does the sheet turn yellow in full specrtum ? I understand that the sheet doesn't reflect UV very well. But the influence of UV in fullspectrum is close to zero...

[Andrea B.]

great investigation. And fun !!

[Andy Perrin]

8 hours ago, Fedia said:

The GBUV looks delicious ! It has the color of a nectarine.

 

A question though, why does the sheet turn yellow in full specrtum ? I understand that the sheet doesn't reflect UV very well. But the influence of UV in fullspectrum is close to zero...

It is starting to darken even in blue, so I think that’s your answer. IR through green are the majority, so it reflects mainly yellow (red/iR + green)

[Fandyus]

15 hours ago, Fedia said:

The GBUV looks delicious ! It has the color of a nectarine.

 

A question though, why does the sheet turn yellow in full specrtum ? I understand that the sheet doesn't reflect UV very well. But the influence of UV in fullspectrum is close to zero...

That is because the full spectrum image is still constructed using the different images I took. It is IR-R vis-G UV-B. It's not a normal full spectrum photo.

14 hours ago, Andrea B. said:

great investigation. And fun !!

Thank you Andrea, I sure had a lot of fun.

[Fandyus]

6 hours ago, Andy Perrin said:

It is starting to darken even in blue, so I think that’s your answer. IR through green are the majority, so it reflects mainly yellow (red/iR + green)

It does? I don't notice any darkening of the sheet in blue. Keep in mind that the white thing on the bottom is a PTFE sheet so I color balanced everything properly.

[Fedia]

2 hours ago, Fandyus said:

That is because the full spectrum image is still constructed using the different images I took. It is IR-R vis-G UV-B. It's not a normal full spectrum photo.

That makes sense, because if the sheet had reflected a little bit less blue it would have been obvious in the visible image.

[Nate]

A lot of work you put into these, turned out excellent.

[Andy Perrin]

2 hours ago, Fandyus said:

It does? I don't notice any darkening of the sheet in blue. Keep in mind that the white thing on the bottom is a PTFE sheet so I color balanced everything properly.

It does look a bit darker to me in blue, but if the full spectrum is not a normal one then your explanation makes more sense! I think that “full spectrum” needs a footnote. 

[Fandyus]

6 hours ago, Nate said:

A lot of work you put into these, turned out excellent.

Thank you! I spent about four hours today making the same series on an onion cross section. I will post eventually when I process all the data. It's been very fun for me.

[Fandyus]

6 hours ago, Andy Perrin said:

It does look a bit darker to me in blue, but if the full spectrum is not a normal one then your explanation makes more sense! I think that “full spectrum” needs a footnote. 

I see. Well I can only say that the fabric is very white in real life so I'm not sure. Maybe it seems darker to you since subsurface scattering drops slightly and shadows on the bumps become a little harsher.

[Unscenerie]

Does the IR portion (such as "IR only stacked") show heat discharge?

[ulf]

3 hours ago, Unscenerie said:

Does the IR portion (such as "IR only stacked") show heat discharge?

It can do that in the right conditions with things that are hot enough. Search on the forum for "soldering iron emit enough NIR" to find my post showing that.
Normally thermal cameras work at a far longer wavelength than the silicon based camera sensors in normal cameras can detect. That stops a smidge above 1000nm.

https://www.ametek-land.com/pressreleases/blog/2021/june/thermalinfraredrangeblog

[Stefano]

I think this is the post Ulf is referring to: 

Objects at room temperature or even significantly higher (maybe below about 300 °C) are too cold to emit detectable amounts of near infrared light, but with a full-spectrum camera you can see incandescence below the Draper point, which is the temperature where the human eye will start to see a red glow, about 525 °C.

 

Very hot objects emit detectable amounts of UV as blackbody radiation.

[Unscenerie]

Amazing. IR photography (and UV) is full of mysteries, and y'all uncover those mysteries.

 

I'm thinking, though. Why would cucumbers emit NIR light? They can't be hot enough, right? 

[Stefano]

Unless you put them in a 300+ °C oven, they won't glow as seen from a "conventional" full-spectrum camera.

 

Room temperature objects don't glow even in SWIR (<2000 nm or so). You start seeing people glow in MWIR.

[Alaun]

You do not see the ir of the cucumber because it has the same temperature as the surrounding, so all the „same color“.  If you put the cucumber in front of a colder -or very cold- background, you can easily detect that it emits a lot of ir and nir.

[Stefano]

Yes, but not at normal temperatures, unless you are using a MWIR or LWIR camera. It simply wouldn't glow bright enough.

[Andy Perrin]

Stefano is correct- the cucumber emits negligible nir in normal surroundings for a camera like ours to pick up, no matter how dark the background. It’s not just signal to noise ratio, Alaun. If you plug 300K into Planck’s law, you can see how small the signal would be at 1000nm. I doubt our cameras would be enough. This is why we need LWIR cams or MWIR cams, with sensors to pick up the much stronger long wave radiation. 
 

cucumbers can still emit near IR by fluorescence though, but that is unrelated. 

[Alaun]

Off course, you need special equipment!

 

My comment was intended just as a short answer  to Unsceneries question,

whether there is radiation (there is); sligthly expecting more comments,

when I wrote "... you can easily detect ..." ;-)

 

E.g. if your camera sensor has the same temperature as the cucumber,
the thermal noise of the sensor is probably on the same level as
that of the cucumber, so it will be a kind of blind.

 

 

Werner

[Fandyus]

On 8/16/2023 at 8:05 AM, Unscenerie said:

Does the IR portion (such as "IR only stacked") show heat discharge?

No - it highlights the reflectance consistency in the given spectrum. If I stacked the three visible channel this way, I believe I would basically get a map of saturation.

[Fandyus]

On 8/17/2023 at 2:58 AM, Andy Perrin said:

cucumbers can still emit near IR by fluorescence though

Funny you mention that, I have pictures of that too! ;)

 

850nm longpass

 

720nm longpass

 

650-ish nm longpass color enhanced

 

visible