Easy Color Correction With A Gray CardCorrecting your images for accurate color is an easy step that can vastly improve the quality of your images. This tip is especially helpful if you are shooting at night using daylight balanced bulbs because even though bulbs are 'balanced', sometimes they still need correcting.
Different types of light bulbs emit varying degrees of color temperature which if not corrected can create unpleasant color casts. A gray card is a really inexpensive tool that can help you with this very task!
Step #1 - Purchase a Gray CardGray cards can be purchased at your local photography shop. All they are really are a piece of cardboard that has a flat, neutral gray color painted on one side. These cards cost around $5 dollars. Some shops sell super expensive gray cards that cost around $40 dollars, so be careful when asking the shop owner for one. You don't need the super expensive card, believe me!
Step #2 - Position Gray CardThe next step is to set up your lights, plates, and setting. Before placing the food on the plates carefully position the gray card on the plate so that it faces the camera. It's important that the card not be in shadow or in a highlight glare. You could also have someone hold the gray card like in the picture above, just make sure that the card is under the same exact light that the final photo will be in.
Step #3 - Take A Picture Of The Gray CardSounds sort of weird, I know, but just take it. Set the proper exposure and take a picture of the gray card. The position of the camera, composition, and lighting should all be similar to what the final picture will be. Once you take this picture, continue shooting your food like you normally would (without the gray card!). You only have to take a picture of the gray card once....unless the lighting changes. If the lighting changes take a new picture of the gray card and continue shooting like normal.
Step #4 - Set Gray Point In PhotoshopOpen the image in Photoshop and add a levels adjustment layer. (If you're not familiar with adjustment layers, check out this easy tutorial that explains the benefits of Non-Destructive Image Adjustments) In the Levels adjustment window, on the lower right hand side, you will see three eye-dropper icons.
Click the middle one. While selected, any pixel you click will automatically be converted into neutral middle gray---shifting all the colors in the image along with it.
Once the middle gray eye-dropper tool is selected, bring the cursor over to your image and click anywhere on the gray card. Voila! The image is automatically neutralized of any color casts!
Step #5 - Save and Load CorrectionOnce the correction is made find the "save" button in the Levels adjustment window and click it. The button is on the right hand side of the histogram. This will save the adjustment and will allow you to load it into any image. Name the file with the date of the shoot and a descriptor like "color-correction". Photoshop will ask you to specify a location to save the file so pick something that will be easy to remember.
With this adjustment saved, all you have to do now is open up your images that you shot after taking the picture of the gray card and add a new adjustment layer. Once the Levels adjustment window is open, click "load" and select the saved adjustment file and Voila! A perfect color corrected image!