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Graphic Communications
GRA 323
Natalia L

CHAPTER 4: COLOUR CORRECTION Images  light, medium, dark areas of colour 5 tonal ranges: highlights, one-quarter, mid, three-quarter, shadows (average tonal ranges) measuring in values of CMYK; highlights 5-15% one-quarter tones 15-35% mid-tones 35-65% three-quarter tones 65-85% shadows 85-95% Ideally, an image should have good contrast between light and dark tonal ranges High Key Images Low Key Images Average Key Images mainly light in all three tonal dark in all tonal areas most of the colour information ranges lots of shadows and dark in mid-tone range pale an lacking shadow detail Histogram (Levels) Photoshop majority of colour is to the left high key image in one-quarter tones majority of colour is to the right low key image in three-quarter and shadow tones Adjusting Colour Balance Photoshop use eyedropper tool to tell if your image needs colour correcting  setting black and white points corrects 80% RGB values should be equal, if not  colour cast In highlighted areas In darkest areas RGB should not be +245 on average RGB values should not be -10 on average if +245, light areas will appear washed out/lack If -10, shadow areas will fill and lose detail when detail when printed printed Correcting Colour Casts w/ Curves allows you to decrease/increase w/in various tonal ranges more flexible than using Variations, which can ruin image if overused can use Levels too, but Curves is better correct each channel individually make contrast between one-quarter, mid, three-quarter tones distinct enough so contrast in each channel resembles normal black and white photo Example: yellow cast red/green channel are overexposed, blue channel is underexposed Colour Correcting Skin Colours Caucasian M, Y = with M tones slightly higher, C=1/3 M,Y Asian  more yellow +10% Black less magenta than other races, CYMK high overall Curves Window Photoshop moving points UP will darken the tones, removing light from that tonal range moving points DOWN will lighten channel, bring more light to tonal range don’t move too far, ruin picture S curve contrast in channel is weak, colour range btw/ 1-3-quarter tones are low flat image The gentle valley all tonal ranges need to be lightened The sharp slope darken two tonal ranges, locking pt. on quarter-tones, single pt. raised on 3-quarter tones Twin peaks useful for where not enough contrast btw/ mid-tones and other tonal areas CHAPTER 5: RESOLUTION Bits and Bytes  pixels broken into smaller pieces of info  24 bit RGB called bits  32 bit CYMK  min. of 1 bit per pixel  better printing results 16 bits per channel  max of 64 bit
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