Would you use a Grey Card function in a phone app?

[etherial]

This might be a strange question. I have an app on my phone (HTC Desire) that has all sorts of photography related resources, like DOF calculator, exposure reciprocation calculator, flash exposure, color temps chart, sunrise sunset times, moon phases etc etc. It is very useful!

Anyway, I just found that it has a grey card function, where it gives you a blank grey screen. Now this just doesn't seem right to me. Wouldn't the screen brightness of your phone screw with that and your WB would just be rubbish? I'm just not sure it is something useful? Any thoughts?

[kiwi]

Wb just needs a neutral colour really

[etherial]

Yeah I guess, but wouldn't an LCD screen have a certain hue about it? After all, it is a light source. I'm just not sure about this one.

[kiwi]

Depends on the screen I guess, my iPhones colors are actually really accurate

[JazzXP]

Pointless. iPhone is emitting light, whereas you want your actual light sources to bounce off the grey card for your settings.

[dieselpower]

Etherial - I'm interested to hear what this wonder app is. I'm using a Windows touchscreen phone also and can do most of the above with several different apps, but one app to do it all would be great...

[etherial]

Etherial - I'm interested to hear what this wonder app is. I'm using a Windows touchscreen phone also and can do most of the above with several different apps, but one app to do it all would be great...

This is on an Android device (much better OS than Apple or Windows Phones ). The app is called "Photo Tools" and its developer is hcpl. Their website is http://android.hcpl.be/

Not sure they do one for other platforms. I don't mind it, it puts a few handy tools in your pocket when you're out and about.

[etherial]

Pointless. iPhone is emitting light, whereas you want your actual light sources to bounce off the grey card for your settings.

That makes a lot of sense. It is a light source, so how can it act as a greycard for your camera to meter ambient light. Well said.

[arthurking83]

That makes a lot of sense. It is a light source, so how can it act as a greycard for your camera to meter ambient light. Well said.

yeah!.. but that's only if you want to use the grey card as an exposure reference point!

Because the illuminated grey reference point(the phone app) is constant, it will appear to be the same brightness to the camera whether it's bright or dark.

BUT as a WB reference point the camera doesn't really take into account the brightness level, all it's looking for is a grey colour(at 18%) as a reference point.

If you use Manual WB setting and take the shot of the phone app the camera will simply process the info it requires quicker. The camera is only looking for something grey, and tries to expose it according to it's meter's requirement for a neutral exposure. But all it wants is to know how grey in colour the grey reference point is ... not how bright it is.

This app may or may not work, as already mentioned it'll depend on the screen hue, but I suspect that it'll be within 5-10% accurate(good enough). Unless the screen is obviously cast with another colour contamination like blue, green, red, it should work OK.

[soulman]

Actually, I don't think the fact that it's a light is the problem. There is no particular reason that a screen can't end up having 18% reflectance, even though it is emitting light. It can be light, it can be dark; it can be 18%. The problem would be getting a screen adjusted so it would have that value. Phones have LCD screens similar to the ones we all use with our computers and they would need to be calibrated to a degree that would be hard to achieve with an Eizo let alone a phone. Then you have the added issue of the screen cover, which will affect the reflectance significantly. Not going to happen - it's a crock.

[arthurking83]

if the phone had an inbuilt ambient light meter device to allow it to maintain a set brightness level regardless of the ambient light it would still work as an exposure meter too. How accurate it would be is another question, and not to be relied upon, unless you can test accurately under controlled conditions.

I think it'd still work 'quite accurately'(but not perfectly) as a WB reference point. Just make sure if you try to use it in that manner, that the camera is only seeing the grey part of the phone's screen. Phone being as small as they are would make that annoyingly hard(but at least you don't need to focus to get a WB reference point).

[soulman]

I see what you're saying, but there is usually no way to adjust the colour balance or luminance of a phone's screen and there is no way they'd get calibrated in the factory for exacting photo work. Even if it were calibrated, it has to be redone regularly to stay accurate. Good phone screens are pretty good, but there are a lot of variables that would be difficult to eliminate or compensate for.

Anyone who is particular enough about WB to be setting it in the field like this is going to be particular enough to want it accurate and carrying a grey card is pretty easy.

[etherial]

This is the type of debate I was expecting

I can't see myself using it, there is just too much doubt about this for me, unless someone could convince me otherwise.

Must buy myself a grey card one day though...

[arthurking83]

...

Must buy myself a grey card one day though...

I have one, so next time we catch up(should be soon) we can 'test' the phone app to see how accurate it can be.

I may be a regular traveller to Ballarat soon too over the next few free weekends. My brother is readying his house up there for rental purposes, so I may chip in to help a little here and there

[etherial]

I have one, so next time we catch up(should be soon) we can 'test' the phone app to see how accurate it can be.

I may be a regular traveller to Ballarat soon too over the next few free weekends. My brother is readying his house up there for rental purposes, so I may chip in to help a little here and there

Sounds like a plan!

[soulman]

And I will look forward to seeing the results.

[JazzXP]

yeah!.. but that's only if you want to use the grey card as an exposure reference point!

Because the illuminated grey reference point(the phone app) is constant, it will appear to be the same brightness to the camera whether it's bright or dark.

BUT as a WB reference point the camera doesn't really take into account the brightness level, all it's looking for is a grey colour(at 18%) as a reference point.

If you use Manual WB setting and take the shot of the phone app the camera will simply process the info it requires quicker. The camera is only looking for something grey, and tries to expose it according to it's meter's requirement for a neutral exposure. But all it wants is to know how grey in colour the grey reference point is ... not how bright it is.

This app may or may not work, as already mentioned it'll depend on the screen hue, but I suspect that it'll be within 5-10% accurate(good enough). Unless the screen is obviously cast with another colour contamination like blue, green, red, it should work OK.

I reckon it'd be useless for WB too as the colour of the backlight won't necessarily match the colour of the lighting setup used. If the lights are bright enough to drown out the backlight, then you're not going to see the grey on the screen at all, if they're not, the backlight temperature becomes the issue.

[bigdazzler]

my grey card is a tear out from the back of my Kelby CS4 book ..... talk about opposite ends of the tool spectrum .. Android phones versus bits of paper