Week 3 Part 8: Color correction
(Global Corrections)
Terms to know: Local / Global
Throughout this class I may use terms such as "local" or "global". The meanings of these terms are as follows:
Local
An edit or change constrained to a particular area of an image. Usually confined by a selection.
Global
This would be an edit or change to the entire image so that it affects the whole image dynamically.
Tones of an image (Highlight - Middle tone - Shadow)
When talking about the tone of an image, we are not speaking of any color values. We are only speaking of the light values in all the shades across the image. The lightest shades, including total white, are referred to as highlights. The darkest shades, including total black, are referred to as shadows. Directly in the middle of these two ends of tones are what we call, middle tones, as they fall around the mid-range of your tonal scale. If you wanted to split the tonal range into a few more categories, you could call the tones in between the highlights and the middle tones, quarter tones, and the tones between the middle tones and the shadow, three quarter tones. A good understanding of tonal range can be very advantageous when making adjustments to your photos.
Histograms
An image histogram is type of histogram which acts as a graphical representation of the tonal distribution in a digital image. It plots the number of pixels for each tonal value. By looking at the histogram for a specific image a viewer will be able to judge the entire tonal distribution at a glance. Image histograms can be viewed through many of Photoshops adjustment panels, most often in "curves" and "levels".
Channels
The channels palette displays one composite channel of all the channels combined for your normal viewing mode. Then it will show each individual channel separately in it's greyscale form. You can work solely on individual channels by having just that one channel selected when you do your editing. The eye icon in the left column will turn the display for that channel on or off.
You can have your channels display in their given colors instead of grey if you like by changing the setting in the preferences. Listed in "interface/Show Channels in Color"
Color Balance
Very important to a good quality image is color balance. This should be one of the first, if not thee first correction that should be done when color correcting images. If your color balance is out, everything will be out. Sometimes you can correct an image in one fell swoop just by putting the color balance where it should be. Most critical in the highlights and the shadow. When working in RGB, don't forget that equal values of all threee colors produce a neutral grey. If your image that you are working on has area's that you know are supposed to be grey, then you can use that to your advantage and adjust the balance until that particular area is neutralized. This works well with your highlights and shadows as well. If your photo is a typical photo, chances are it has a highlight in it somewhere that is white, or at least is supposed to be white. On the other end of the scale, it probably has a shadow area that is supposed to be black. By neutralizing these 2 points, you have in many cases, balanced your photo properly. Quite often this adjustment is all the photo needed. You will notice that if you properly balance an un-balanced image, all colors and tones inbetween the highlight and shadow fall right into place automatically.
Curves
One of my most used controls for corrections. This adjustment allows you to make adjustments to your image dynamically in all channels or in individual channels. This is one control panel that shows you the histogram in behind the tonal curve. By using curves you can pinpoint certain tones you want to target in all channels or in individual channels.
Hue and Saturation
Hue and Saturation is a great way to increase the vibrancy of your images. Whether it be in all colors or specific colors this is a great tool to achieve this. Use top drop down menu to choose the colors you wish to affect or leave it on master to affect all colors. This control is based on the HSB color model.
Selective color
This control is also a way to edit colors but you can selectively choose color shades to limit where your edits take place. You can also use it to selectively alter whites, neutrals and blacks. This control is based on the CMYK color model. Somewhat similar to the Hue and Saturation control but based in the CMYK model.
Unsharp masking
This is a very powerful tool used to add sharpness to your images. Don't be fooled by its name "unsharp" masking. This term dates back to a old traditional method of sharpening images back in the days of analogue film. The effect basically makes what I call "contour" lines where an area of light tones meets an area of dark tones.
On the light side of things, it will create a lighter contour while on the darker edge it will create a darker contour. This fools the eye into making the image appear sharper. Caution should be taken as over sharpening an image could ruin the look of the picture.
Sample of before and after Unsharp Masking (cursor over the image to see before and after)
