Correcting (whitening) white High Key background in Gimp/Photoshop

[jsl]

Hiya,

I need help!!! I set up a light box and took some product shots (origami works) but on some of these, the exposure wasn't white enough and as such, the background has turned out grey on some of the images. If I had the equipment, I would have ensured the background was 2 stops brighter but unfortunately, I don't.

In Gimp/Photoshop (preferably Gimp), how can I correct the shots that I have already taken? I am pretty sure that I have read of a way to correct these easily without blowing out the detail and without having to use a fine brush to paint around the detail (painfully time consuming). Is there some way of using layers and a screen layer to fix this?

Attached is the photo in question. I would be so incredibly grateful for any advice you could give me. Even if you could just point me in the direction of some online tutorials, that would be great. I've been racking my brain for the key words to google but I can't seem to find anything.

Thank you so much dps people!
Jonathan

[wulf]

Do you know how to work with layers (including layer masks)? You might want to apply a bit of white balancing (you can use the levels tool to set white, black and grey points) and possible additional brightening with a copy of the layer in screen or overlay mode; using a maks means you can then "paint" that effect in or out using a soft edged brush or airbrush. You can start with a large brush and gradually step down until you have blended the layers to your satisfaction.

Wulf

[jsl]

Originally Posted by wulf

Do you know how to work with layers (including layer masks)? You might want to apply a bit of white balancing (you can use the levels tool to set white, black and grey points) and possible additional brightening with a copy of the layer in screen or overlay mode; using a maks means you can then "paint" that effect in or out using a soft edged brush or airbrush. You can start with a large brush and gradually step down until you have blended the layers to your satisfaction.

Wulf

Hiya Wulf,

Thanks for the tip. I'm fairly new to post processing but am learning my way through Gimp (you recommended it to me - thanks!). I think I can get a duplicate layer with the "correct" white background but it's taking me quite a while to "paint" in the correct image. Is there a quicker way I can do this or a trick I can use with selection tools?

[Trader]

Yes, there is a very quick way (I just did it). I used Photoshop, add a Levels adjustment layer and choose the "Sample White Eye dropper" Click on the upper right corner and it will automatically adjust your entire image to reflect the ture colors.

[jsl]

Originally Posted by Trader

Yes, there is a very quick way (I just did it). I used Photoshop, add a Levels adjustment layer and choose the "Sample White Eye dropper" Click on the upper right corner and it will automatically adjust your entire image to reflect the ture colors.

Hi Trader,

Thanks for your suggestion. However, I had already tried this and doing this bleaches out the subject (the origami). I reckon the solution is along the same lines though - just need to somehow select the white area and feather it somehow - but I'm not sure how to do this.

[wulf]

The top left portion might have the origami a bit bright for your tastes but shows a pure white background; in contrast, the bottom right shows the original image which has a background that looks a long way from white when set next to the purer version.

I took three steps to create the top left image. Firstly, I created a duplicate layer and used the levels tool to set white, black and grey points (the three droppers towards the bottom of the dialog box). I then created a duplicate of this layer and used the curves tool to tweak it further. Both were judged by eye and I held back on the adjustments to avoid blowing out the detail of the origami, which meant the background wasn't perfectly white.

Thirdly, I added a blank white layer to which I applied a white layer mask. To finish off, I took a large soft-edged brush and used this to paint back in the subject in the centre. Large meant that it was very quick to apply; soft-edged blended the near-white background of the photo with the pure white overlay. If you use the eye dropper tool on the image above, you will see that the top edge is pure white (#ffffff) but a sample from nearer the centre, which still looks pure to the eye, is more like #fefefc.

However, the blend is so subtle that you can't see it. You could almost apply the final stage without bothering with the first two but if you get the background as close to white as you can, it is much easier to quickly get a seamless result.

Wulf

[jsl]

Hi Wulf - you saved the day again! Thanks so much for your advice. This was exactly the solution I was after. I tried it out and managed to get some good results. I have yet to learn about how to find the correct grey balance but that can wait.

Thank you so much for your prompt advice. As always, I find your "mini-tutorials" incredibly helpful. Next, you'll be trying to persuade me to do away with my Canon and go Nikon!