Getting gray background using white paper

Started Jun 26, 2013 | Questions
YonathanZ
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Getting gray background using white paper
Jun 26, 2013

Hi,

I am trying to take macro shots of jewelry using focus stacking. I know how to focus stack but my problem is with lighting - I do have CFL bulbs and tungsten ones and a light tent. There's also the DSLR's built in flash (which I don't ever use, but it's there).

Anyway, my photos turn out to be grey, as in, I can't get a pure white background. I am using A4 paper (not recycled, so it's "very white") as the background on which I lay the jewelry (necklace or whatever) but the result does not have a white background.

Here's an example of a photo using tungsten light from real close (500W projector about 15 cm above the subject) to rule out the possibility of lack of light.

Before I fixed auto balance with a gray card:

No WB.

And after WB using Lightroom:

After WB.

As you can see, I didn't use focus stacking here, it's just a single shot, without a tripod or anything, just to get the colors. Another thing you can see is that the paper looks more like recycled paper, while in reality it's very much white.

Since we can rule out lack of light (at least as far as how powerful the light is; I know I should use balanced light, around 5500K), I wonder what really causes the problem. BTW, the same problem occurs when photographing using a light tent (to diffuse the light).

I shot using Aperture priority mode, f/5.6, shutter at 1/125 (as set by the camera), spot metering (also tried evaluative metering, same thing happens), Canon T3i and a Sigma 105mm f/2.8 macro lens at 1:1 magnification.

Please advise what could cause the problem.

Thank you.

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ChrisBurch
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Re: Getting gray background using white paper
In reply to YonathanZ, Jun 26, 2013

It's not a "lack of light", you have simply exposed the background paper so that it is within the dynamic range of your camera. You will only get pure white if the background is at or beyond the point of being over-exposed. Since you used automatic settings, your camera is trying to make everything in the image properly exposed including the background. You'll have to go to fully manual settings to get what you're looking for.

Since you're using a continuous light source,, you can either slow down your shutter speed or increase the ISO to get a brighter background. If you over expose too much it will flare into the pendant, so keep that in mind.

The biggest catch to increasing the exposure is that you need to get the white background brighter without blowing out the pendant itself. Since you only have one light source, you may find that hard or impossible to do. If so, you can fix in post by increasing your highlights in whatever editing program you use.

A better solution is to get a second light source and light up the background from behind (create a lightbox). That way you can crank up the backlighting without messing up the exposure on your subject. If you have a light tent, you have the translucent material to pull this off...it's just a matter of physically positioning everything to work.

You can also avoid having to focus stack if you use a higher f-stop and/or backing away from the pendant. Unfortunately that will make the photo even darker, so you'll have to increase the shutter/ISO even more to compensate.

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Sailor Blue
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Re: Getting gray background using white paper
In reply to YonathanZ, Jun 27, 2013

Here is my suggestion.

Create a small open frame box out of PVC tubing. Add a side to side crossbar to the middle of the top opening.

Attach a sheet of translucent white plastic or paper at the top back and the front bottom, curving the sheet at the back so that you form what is called an infinity background. Tracing paper found at an office supply or art supply store will work well.  If you tape it to the sides of the box as well it should support your small jewelery.

For heavier items a bent sheet of 1/8th inch white acrylic will work.  I heat gun will help you bend it but be very careful since those guns are very hot and you can overheat the plastic easily.  I suspect a hair dryer may not be hot enough but it is worth trying first.  If you don't want the floor to be reflective you can sand it down until it is dull and non-reflective.

You light the back wall from behind and the floor from below and adjust the brightness of those lights until the all of the sweep of paper just starts to blink when your camera aperture is closed down 1/3 stop from where it will be when you shoot the subject.

Now either lie the product on the floor and light it through the open sides and front. Don't forget to reset the aperture before you shoot.

The result will be shadowless but you will be getting some light from the floor adding to the brightness of the edge of the product touching the floor. This can cause reflections you don't want or even cause the edges to go pure featureless white.

If you want to eliminate the added brightness to the edge of the product then suspend it by a length of fine monofiliment fishing line or white thread. It is easy to take the fishing line or thread out of the image in Photoshop or a similar post processing program.

You can use your light tent the same way but you will have to support it high enough to get the light for the floor under it.

Use all the same type of lights for everything so that you don't have color WB mismatches. Shoot with your camera set to the correct WB or better yet, do a custom WB by closing down the aperture by two stops and shooting the background.

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YonathanZ
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Re: Getting gray background using white paper
In reply to ChrisBurch, Jun 28, 2013

ChrisBurch wrote:

It's not a "lack of light", you have simply exposed the background paper so that it is within the dynamic range of your camera. You will only get pure white if the background is at or beyond the point of being over-exposed. Since you used automatic settings, your camera is trying to make everything in the image properly exposed including the background. You'll have to go to fully manual settings to get what you're looking for.

Since you're using a continuous light source,, you can either slow down your shutter speed or increase the ISO to get a brighter background. If you over expose too much it will flare into the pendant, so keep that in mind.

The biggest catch to increasing the exposure is that you need to get the white background brighter without blowing out the pendant itself. Since you only have one light source, you may find that hard or impossible to do. If so, you can fix in post by increasing your highlights in whatever editing program you use.

A better solution is to get a second light source and light up the background from behind (create a lightbox). That way you can crank up the backlighting without messing up the exposure on your subject. If you have a light tent, you have the translucent material to pull this off...it's just a matter of physically positioning everything to work.

You can also avoid having to focus stack if you use a higher f-stop and/or backing away from the pendant. Unfortunately that will make the photo even darker, so you'll have to increase the shutter/ISO even more to compensate.

Using a light tent, I was able to get a pure white background, but the subject is over exposed, it becomes dull looking. I wonder how I can truly separate the lighting of the background from the lighting of the subject.

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ChrisBurch
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Re: Getting gray background using white paper
In reply to YonathanZ, Jun 28, 2013

If you want to vary the light on the pendant from the background, you will need separate light sources.  If it was a portrait, you would just have the subject step away from the background and have dedicated lights on the background and separate lights for the subject.  You're doing product photography with the subject sitting on the background, so you're options are more limited.  You certainly could separate them if you hang the pendant and use separate lights.  Since you're using a piece of paper for the background, you wont be able to get far enough away from the pendant to apply separate lights.

With the gear you mentioned, your only option is to light the background from underneath.  I wasn't talking about using the light tent in its normal configuration...only to use it as the background instead of piece of paper.  If your tent is one of those free standing collapsible cubes, just put the pendant on the very top of the cube and then stick your light on the inside pointing up.  You'll need a separate light source to light up the pendant from above.  A close reflector might work instead put the reflector above the pendant to bounce the light from the tent back onto the pendant), but you'll have to try it know sure.

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Re: Getting gray background using white paper
In reply to YonathanZ, Jun 28, 2013

YonathanZ wrote:

I wonder how I can truly separate the lighting of the background from the lighting of the subject.

One way is to do it in Photoshop. With this piece of jewelry, it wasn't very hard . I don't use Lightroom, so I don't know what the limitations there might be, but Photoshop can certainly do it with one click of a levels or curves adjustment to set white point at 255.255.255. The mask protects the subject from that adjustment. (I don't know what the true color of this piece is, but it looks a bit drab to me. You could juice that up while you're at ... consistent with reality, of course.)

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Barrie Davis
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Re: Getting gray background using white paper
In reply to YonathanZ, Jun 29, 2013

The camera's metering system is specifically designed to produce an "overall grey" result from what ever it is pointed at. It is succeeding, so nothing is "wrong" as such.

The answer is to give it what it is expecting, and to meter from a grey-toned target instead of a white one. Special grey cards are made for the purpose. The card is held in front of the subject in the subject lighting and the reading taken. Lock the exposure. Take the card away and shoot.

Alternatively, add positive (+) exposure compensation with the Exposure Compensation dial, which is provided for the purpose of correcting light-toned shots.

Note: Minus (-) compensation is used for dark-toned shots.

Judging by the tone of grey you have so-far got, I would expect PLUS 1+1/3 stops of positive exposure compensation would be about right. If it isn't, experiment with different values of positive compensation until you get the background tone you want.

Advice: Light boxes are not a good way of lighting products. The results are very poor for most subjects. Instead, get a good book on lighting and learn how to do the job properly.

"Light: Science and Magic" is highly recommended.
Light boxes (also tents, cocoons, etc.) are not.

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Barrie Davis
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Re: Getting gray background using white paper
In reply to YonathanZ, Jun 29, 2013

YonathanZ wrote:

ChrisBurch wrote:

It's not a "lack of light", you have simply exposed the background paper so that it is within the dynamic range of your camera. You will only get pure white if the background is at or beyond the point of being over-exposed. Since you used automatic settings, your camera is trying to make everything in the image properly exposed including the background. You'll have to go to fully manual settings to get what you're looking for.

Since you're using a continuous light source,, you can either slow down your shutter speed or increase the ISO to get a brighter background. If you over expose too much it will flare into the pendant, so keep that in mind.

The biggest catch to increasing the exposure is that you need to get the white background brighter without blowing out the pendant itself. Since you only have one light source, you may find that hard or impossible to do. If so, you can fix in post by increasing your highlights in whatever editing program you use.

A better solution is to get a second light source and light up the background from behind (create a lightbox). That way you can crank up the backlighting without messing up the exposure on your subject. If you have a light tent, you have the translucent material to pull this off...it's just a matter of physically positioning everything to work.

You can also avoid having to focus stack if you use a higher f-stop and/or backing away from the pendant. Unfortunately that will make the photo even darker, so you'll have to increase the shutter/ISO even more to compensate.

Using a light tent, I was able to get a pure white background, but the subject is over exposed, it becomes dull looking. I wonder how I can truly separate the lighting of the background from the lighting of the subject.

Separation of the subject and background lighting is pretty much impossible inside a tent.

Don't use a tent. Don't use a white bakground.... (white is over-used... there are plenty of other backgrounds out there, almost all of which would look more interesting.)

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YonathanZ
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Re: Getting gray background using white paper
In reply to Barrie Davis, Jun 29, 2013

That's a lot of useful information. Thank you all. I'll try your suggestions and read the book mentioned above.

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Nikonfan99
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Re: Getting gray background using white paper
In reply to Peano, Jun 30, 2013

Last product shoot I did, I made a large box out of white foam board. Used GE reveal bulbs and three desk lamps to create even light on my product. Used a grey card to do my w/b.

Took the images into CS6 and used topaz remask (could have used refine tool in photoshop but remask is faster for me) and extracted the items. Placed them on a white background in photoshop and did not have to worry about any issues and all the shots looked great. Also added shadows where needed.

I think the photoshop extraction method creates an even background that is free from any defects or posterization. This method takes longer but the results are professional and clean.

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24Peter
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Re: Getting gray background using white paper
In reply to Nikonfan99, Jun 30, 2013

Some good suggestions. To recap:

1. The problem the OP is having has nothing to do with the "color" of his white paper; rather it is the level of exposure. "White" paper can be white, gray or black depending on how much light is hitting it.

2. In this case there are only 2 ways to get a true "white" background -

a. light the subject and background separately. Difficult if not impossible if the subject is resting directly on the background. Separate the two. Clear Plexiglas raised off the background is a good way. For jewelry, I also often hang the item in front of a white backdrop and light the item separately that way;

b. use Photoshop and do a knockout to remove the background and replace it with pure white. This involves creating a selection. This can be done with one of the selection tools or the pen/path tool. Often difficult/time consuming with silver/reflective jewelry. You can create a shadow in Photoshop once your extraction is complete if you want more realistic look.

I actually usually do both a. & b. with silver (and sometime gold) jewelry since lighting the item separately also helps with getting a good selection in Photoshop.

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Re: Getting gray background using white paper
In reply to 24Peter, Jul 1, 2013

24Peter wrote:

You can create a shadow in Photoshop once your extraction is complete if you want more realistic look.

Footnote: If the subject has a natural contact shadow, it's often better to preserve that while masking.

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24Peter
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Re: Getting gray background using white paper
In reply to Peano, Jul 1, 2013

Peano wrote:

24Peter wrote:

You can create a shadow in Photoshop once your extraction is complete if you want more realistic look.

Footnote: If the subject has a natural contact shadow, it's often better to preserve that while masking.

Ideally I would agree, but - and I'm sure it's just my mediocre Photoshop selection skills - I find natural contact shadows a huge PITA to preserve in a way that looks natural when doing knockouts. Got any tips?

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Re: Getting gray background using white paper
In reply to 24Peter, Jul 1, 2013

24Peter wrote:

Peano wrote:

24Peter wrote:

You can create a shadow in Photoshop once your extraction is complete if you want more realistic look.

Footnote: If the subject has a natural contact shadow, it's often better to preserve that while masking.

Ideally I would agree, but - and I'm sure it's just my mediocre Photoshop selection skills - I find natural contact shadows a huge PITA to preserve in a way that looks natural when doing knockouts. Got any tips?

Right, some can be a royal pain, not worth the trouble. It depends on the particular image. With the one I did above, I was able to select outside the shadow and then feather the edge of the mask.

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