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Photoshop Basics
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Luminous Range

• To retain the highest range of luminosities at
  EACH conversion.

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Luminous Range

• Use the best image sources
• IF possible scan to 16-bit greyscale
• Ensure scanner settingsdeliver a histogram
  showing even distribution over the full range.
• Scan the image
• to the highest
• resolution
• you can

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Colour

• The colour that you SEE is influenced by
• Any funny desktop coloursor artificial light

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Resolution

• In the real world, the resolution that we achieve
  is governed by
• Focus
• Resolving power of lens
• Camera Shake
• Heat Haze

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Scanner

• Always control the dynamic range of each colour.
• Never over-saturate.

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Conclusion

• Never throw information (colour or resolution
  away) unless CROPPING

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All pictures are composed of pixels
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All pictures are composed of pixels
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Binning and Histograms
First count the number of black pixels
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Binning and Histograms
Next count the number of dark grey pixels
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Binning and Histograms
Repeat for all shades of grey
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Binning and Histograms
Note the fact that, as there are equal numbers of
shades 1 and 2, this produces a flat top
mountain.
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Histograms

• In Photoshop there are 256 bins per colour (R,G
  and B) represented over 256 pixels.
• In a typical picture there may be 3M pixels and
  this is represented by the area of the histogram.

0
255
3M
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Some Typical histograms
NormalCentre weightedClearly drops to zero at
both ends.
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Some Typical Histograms
High KeyLight end weightedBut still clearly
drops to zero at both ends.
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Some Typical Histograms
Low KeyDark end weightedBut still clearly drops
to zero at both ends.
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Perfect Exposure
Data in the histogram is totally contained within
the box at light and dark ends.
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Perfect Exposure - Highlights

• The acid test of perfect exposure is that fine
  detail is revealed in the highlights when the
  light end of the curve is pulled dramatically
  down.
• The bias of the histogram shifts to the dark end.

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Perfect Exposure - Shadows

• The acid test of perfect exposure is that fine
  detail is revealed in the shadows when the dark
  end of the curve is pulled dramatically up.
• The bias of the histogram shifts to the light end.

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Over Exposure
Data in the histogram is clearly off scale at
light end.
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Over Exposure - Highlights

• The acid test of OVER exposure is that fine
  detail is LOST in the highlights when the light
  end of the curve is pulled dramatically down.

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Under Exposure
Data in the histogram is clearly off scale at
dark end.
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Under Exposure - Shadows

• The acid test of UNDER exposure is that fine
  detail is LOST in the shadows when the dark end
  of the curve is pulled dramatically up.

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The Perfect Image

• The histogram (Combined Luminosity) would look
  like this

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The Perfect Image

• The RED histogram would look like this

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The Perfect Image

• The GREEN histogram would look like this

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The Perfect Image

• The BLUE histogram would look like this

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The Im-Perfect Image

• Contrast Range too HIGH

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The Im-Perfect Image

• Contrast Rangetoo BIASEDto High Key

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The Im-Perfect Image

• Contrast Rangetoo BIASEDto Low Key

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The Im-Perfect Image

• Contrast Range too LOW

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The Im-Perfect Image

• Low Key,High Key butLow Contrast

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The Im-Perfect Image

• Colour Cast

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Too Much Flash
Open the picture of too much flash
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• Copy the photo layer
• Change the layer mode from Normal to Multiply

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Layer mask icon

• Add a black layer mask
• Press Alt Key and click the Layer Mask icon
• Change Foreground colour to white.

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• Choose a soft edged brush, paint over the
  foreground area in the photo

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After
Before
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Fixing Underexposed Photos
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• Duplicate background layer (Control-J)
• Change Blend Mode from Normal to Screen. This can
  lighten the photo

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• It still not properly exposed.
• Copy the layer until the exposure looks about
• right (by press Control-J)

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After
Before
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Dodging and Burning Done Right

• Add some highlight of the temple
• Darken the water and sky

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• Create a new layer
• Change the mode to Overlay
• And click the box fill with Overlay-neutral
  color

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• Switch to Brush tool, choose a large soft-edged
  brush, go to options bar and lower the Opacity to
  approximately 30
• Change the foreground color to black (or press
  d)
• Paint over the areas that you want to darken
• Change the foreground color to white (or press
  x)
• Paint over the areas that you want to do
  lightening

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QUESTION AND ANSWER
End