H. Dols

Introduction to digital photography

PPS 6 May 1999 •What are we talking about?

• Digital versus Analog. Can a pictures from a digital camera really match an average Nanyang print. ??

•Resolution!

•Photographic print resolution = under 400 Dots Per Inch (dpi)

•Negatives/slides contain over 2000 dpi

•Our eyes only distinguish about 300dpi

•Computer screens (svga) manage about 72 dpi

H. Dols

Introduction to digital photography

PPS 6 May 1999 •File Formats?

• Large .gifs versus lossy .jpegs and difficult Kodak .pcd files.

•Most common formats!

•.tif or .gif bitmaps formats which reproduce the full picture information. Disadvantage large files and .gif only works in 256 colours. Advantage portable

•.jpeg files are a factor 10-20 smaller (for average photographs) however the format loses picture information mainly in colour gradation that is not observed by the human eye.

•Kodak photocd .pcd is a lossless format but only Kodak is allowed to produce the files. Mainly used for professional work.

H. Dols

Introduction to digital photography

PPS 6 May 1999 •What are digital files anyway?

• 8, 16 bit resolution 24 bit colours what are they.

•Colour resolution!

•8bits=1byte, 1000byte=1Kbyte, 1000Kb=1Mbyte, 1000Mbyte=1Gbyte

•With 8 bits you can specify upto 256 levels, 16 bits more than 65000 colours and 24 bits can grade in millions of steps.

•An 300*300dot .tif scan in 256 colours takes about 300*300*8=90Kbyte

•a similar full 10E6 colour scan wil need 300*300*24=360Kb

•The same full colour picture in jpeg would compress to 20-30Kb

H. Dols

Introduction to digital photography

PPS 6 May 1999 •What options are there for digitizing files ?

• Printscans

• Filmscans

• Digital camera’s

•Print scanners, affordable and reasonable resolution (600dpi) (B$140-900)

•Film scanners, expensive (for high quality) (2700dpi) only option for slides and good option for negatives. (B$ 600-4000)

•Digital cameras. Lower resolution not comparable to film emulsion, yet. Easy to use and cheap to operate. (B$ 500-1800) The multi megapixel cameras now hitting the market are approaching point and shoot quality. (2.1

million pixels = 1600*1200)

H. Dols

Introduction to digital photography

PPS 6 May 1999 •Example resolutions ?

•75dpi

•150dpi

•300dpi •600dpi

H. Dols

Introduction to digital photography

PPS 6 May 1999 •What can we do with a simple scan ??

•Steve Holyoak shows some digital image manipulations he applied to one of his Sipadan Underwater photographs.

•First an A4 print was scanned at 150DPI, in 10e6 colours and loaded into Adobe Photoshop for further manipulation

•The original 6 Mbyte image was cropped to 4 Mb and than corrected as the subsequent slides will show.

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Full scale scan

First optimise the layout C r o p p I n g :

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cropped scan

Now Get rid of some background noise 1 Pixel de-speckle :

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Despeckled scanSharpening introduces to much noise so the Turtle

body is selected separately and sharpened separately

Sharpen specific area :

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Sharpened turtle bodyNext the red that is lost

underwater will be added again +30% and Blue

recuced 15% to give more natural colours

Colour correct (gamma correction) :

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Red / Blue correction

Heavy correction of background and clone some

background over blemish along fin

Despeckle background and clone :

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Corrected background and blemish on fin

Improve contrast in white of body

-15% brightness over selected polygon

optimise contrast locally :

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Brightening and edge correction

For the final picture add some text

finish with conversion to .jpeg =.35Mb

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350Kb jpeg

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Comparison pictures 190% size

Original 150dpi scan

Corrected 150dpi scan Original 300dpi scan

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Some simple filters explained

Original 200dpi scan

Edge enhance light Edge enhance heavy

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Some simple filters explained

Buttonised Horizontal edge enhance gamma correction

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Some simple filters explained

Gamma correction embossed Vertical edge

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•Example from Michiel de Groots Fuji MX700 camera (B$1000)

•Resolution is limited by screen resolution (1280*1024*10E6col)

•Last word on digital cameras

•Can a pictures from a digital camera really match an average Nanyang print. ??

•Judge for yourself!

Introduction to digital photography

PPS 6 May 1999