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In search of Digital quality by Philip Lawson FRPS DPAGB

In search of Digital quality by Philip Lawson FRPS DPAGB. 2 nd Computer. 2 nd Computer Home built 2 x 1 GHz P4 with 2Gb Ram, 180 Gb Disc, 24” Monitor and a Wacom A4 tablet. 2 nd Computer 3 rd Printer. Printer defects Resolution Banding Colour Profiling Paper.

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In search of Digital quality by Philip Lawson FRPS DPAGB

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  1. In search of Digital qualitybyPhilip LawsonFRPS DPAGB

  2. 2nd Computer

  3. 2nd ComputerHome built • 2 x 1 GHz P4 with • 2Gb Ram, 180 Gb Disc, • 24” Monitor and • a Wacom A4 tablet.

  4. 2nd Computer • 3rd Printer

  5. Printer defects • Resolution • Banding • Colour Profiling • Paper

  6. <- Epson 1520 (4 colour) Epson 1270 (6 colour) -> <- Epson 7600 (7 colour)

  7. 2nd Computer • 3rd Printer • 3rd Scanner

  8. Scanner defects • Resolution • Dmax • Colour Profiling • Emulsion

  9. <- Nikon LS20 (Coolscan II) 2700 dpi, 24-bit, 2.7 DMax Minolta Scan Multi -> 2820 dpi, 36-bit, 3.6 Dmax <- Minolta Scan Multi Pro 4800 dpi, 48-bit, 4.8 DMax

  10. Ink-Jet Printer Technology • Colour is created by thepartial overlaying of translucent inks in theform of small dots. • At 1440 dots per inch (dpi), this is too small to be visible to the naked eye, even close to. • BUT…

  11. Resolution and Tone 1 • Ideally each part would be printed with the correct shade of grey – painting. 0 50 125 250 0% 20% 50% 100%

  12. Resolution and Tone 2 • But as each ink droplet can either be present or not, need to dither (16x16) 0% 100% 20% 50% 80%

  13. Resolution and Tone 3 • Variable Droplet Technology significantly reduces this dither patch (8x8) and therefore increases resolution • NB True percentages not known 0% 33% 4 picolitres 66% 100%

  14. Resolution and Tone 4 • Variable Droplet Technology (3) gives more even coverage 33% 66% 0% 100% 20% 50% 80%

  15. Resolution and Tone 5 • Ink Technology further reduces this dither patch (6x6) and therefore increases resolution • 6 Colour • Small Gamut 100% 100% 50% 100% 50% 100%

  16. Resolution and Tone 6 • Variable Droplet Technology + Multiple Colour Inks gives more even coverage 50% Grey by DitherEpson Stylus 1520 50% Grey by VDT Epson Photo 1270/90 50% Grey by 6C Epson Photo 1270/90 (dependant onCMYK profiles and K transfer function) 50% Grey by SGI Lyson

  17. Paper • Choose correct inks and loading to avoid bleed and metemeric effects. • Natural History, Architecture • Super Gloss; Gloss Film, Reverse Film • Portraiture, Landscape • Semi Matt, Art • Creative • Art

  18. Printer Conclusions • Replace every 5 years • Do not induce further aliasing – final file resolution should be factor of print head matrix – e.g. 360 for Epson • Find a Profile, Calibration or Quadtone that suites printer/paper combination and stick to this. • Find and stick to papers you like.

  19. Scanners 1 - DPI • 2000, 2700, 4000, 4800 ??? • Go for max but be prepared for extraordinary file sizes and slow processing. • Avoid Interpolation

  20. Scanners 2 – Clean and Focus • Avoid any “Auto” cleaning gadgets or software • Always Spot retouch the master by hand • If possible try to focus manually and concentrate on the point of interest • Manual focus requires feedback • Films are rarely flat to the required degree

  21. Scanners 3 – Dynamic Range Blocked Slide Increasing Film Latitude Density Negative Base Light Intensity

  22. Scanners 4 – Dynamic Range Thin/Thick Emulsions Blocked Increasing Film Contrast Density Fogging or Pre-flashing Base Light Intensity

  23. Scanners 5 – Dynamic Range Blocked Density Base Exposure Light Intensity Zonal

  24. Scanners 6 – Dynamic Range Slide Increasing Dmax Blocked Negative 4.8 Density 4.0 3.6 2.9 Base Light Intensity

  25. Scanners 7 – Dmax and Bits • No direct correspondence • Typically • Dmax = 2.9 8-bit (1 in 256) • Dmax = 3.6 12-bit (1 in 4,096) • Dmax = 4.0 14-bit • Dmax = 4.8 16-bit (1 in 65,535) • Pseudo Dmax increase by Over-sampling (2N per bit)

  26. Scanners 8 – CCD Noise • Prevalent in Dark areas • Exaggerated by Curve correction and Sharpening in Photoshop

  27. Scanners 8 – CCD Noise Cure? • Greater Dmax, 14+ D to A resolution • Use 2 passes with long exposure second pass and carefully combine.

  28. Scanners 9 – Usage • Must use a scanner that permits • Independent Red, Green and Blue Exposure • Independent Red, Green and Blue Level Trimming • Unnecessary to have • Independent Red, Green and Blue Curve Trimming

  29. Scanners 10 – Histograms 1 • Take readings ONLY on good areas, but include as much of picture as possible.

  30. Scanners 10 – Histograms 2 • Trim Levels • Colour Balance and maximum dynamic range

  31. Scanners 10 – Histograms 3 • Grey Point Levels • Colour Balance and redistribute

  32. Working with Photoshop 1 • Import and work in 16-bit mode for as long as possible[converting to 8-bit just before printing] • Only use CURVES and beware of ALL other adjustments[unless for a quick preview] • Convert the image to 360 dpi in Photoshop[if printing on a 1440 dpi dot-matrix (inkjet) printer]

  33. Working in 8-bit mode 8-bit mode is a scientific description for the fact that the shades of grey are described by an 8-bit binary number. Mathematically, 8-bit numbers can represent anything from 0 to 27-1, 0 to 255 to you ‘n’ me. That is 256 shades of grey 255 128 0 Whilst you cannot see the individual shades, this does have serious repercussions.

  34. Working in 8-bit mode When you work in 8-bit mode, the luminosity (grey or colour) is defined by 256 shades of grey.Each shade of grey is defined like the individual legs of a millipede with 256 legs from white to black.

  35. Working in 8-bit mode For the purpose of understanding, imagine this millipede crossing a cattle grid with 256 gaps. Every leg falls down the gap. In this analogy, every single colour exists and is displayed. 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66

  36. Working in 8-bit mode The Histogram shows the number of pixels in the image (or selection) of each shade of grey.In the original 8-bit grey scale, every single shade of grey exists in approximately equal proportions.

  37. Working in 8-bit mode When you modify the curve, you redistribute the legs. Stretched Compressed

  38. Working in 8-bit mode When you modify the curve, you redistribute the legs.But where you stretch the millipede, you leave gaps [no leg, so no corresponding shade of grey creates posterisation]. Stretched 35 36 39 42 45 48 51 54 57 58 59 60 61 62 63 64 65 66 Missing Shades of Grey

  39. Working in 8-bit mode When you modify the curve, you redistribute the legs.But where you stretch the millipede, you leave gaps [no leg so no corresponding shade of grey creates posterisation].

  40. Working in 8-bit mode Where you compress the millipede, you double the number of pixels with certain shades of grey – but cannot create any intermediate, half tones. There is no such thing as grey 128.5

  41. Working in 16-bit mode Performing the same operation in 16-bit mode has the same effect, but here you are dealing with 65,536 shades of grey (legs).NB. Histograms only show 256 levels.

  42. Working in 16-bit mode Extreme manipulation of the curve, to reveal shadow detail, severely redistributes the histogram and appears to leave many missing shades.

  43. Working in 16-bit mode However, when the 16-bit mode is finally converted to 8-bit, 65,536 shades are “squeezed” down to 256 and the histogram becomes smooth again – no missing shades.

  44. Working with Photoshop 2 • Never carelessly use: • “Auto” anything • Brightness, Contrast, Saturation, Lightness, Colour Balance, Channel Mixer increase • RGB Curve modification with R, G or B Curve modification • Variations • Filters

  45. The Perfect Picture

  46. The Perfect Histogram . . .

  47. is like a Brontosaurus MeetGertie

  48. spanning all the shades of grey

  49. spanning all the shades of grey What NOT to do with your Brontosaurus

  50. If you increase the Brightness Increasing the brightness by +20 shifts the histogram to the white end. All shades of grey have 20 added to them. Values 235 to 255 are “capped” at 255 and highlight detail is lost.

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