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In search of Digital quality by Philip Lawson FRPS DPAGB.

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Presentation on theme: "In search of Digital quality by Philip Lawson FRPS DPAGB."— Presentation transcript:

1 In search of Digital quality by Philip Lawson FRPS DPAGB

2 2 nd Computer

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

4 2 nd Computer 3 rd Printer

5 Printer defects Resolution Banding Colour Profiling Paper

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

7 2 nd Computer 3 rd Printer 3 rd Scanner

8 Scanner defects Resolution Dmax Colour Profiling Emulsion

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

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

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

12 Resolution and Tone 2 But as each ink droplet can either be present or not, need to dither (16x16) 0% 50% 100% 20%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%66%100%33% 4 picolitres

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

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

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

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 Density Base Blocked Light Intensity Increasing Film Latitude Slide Negative

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

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

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

25 Scanners 7 – Dmax and Bits No direct correspondence Typically Dmax = bit (1 in 256) Dmax = bit (1 in 4,096) Dmax = bit Dmax = bit (1 in 65,535) Pseudo Dmax increase by Over- sampling (2 N 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 , 0 to 255 to you ‘n’ me. That is 256 shades of grey 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

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 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 Meet Gertie

48 spanning all the shades of grey

49 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.

51 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.

52 If you decrease the Brightness Decreasing the brightness by -20 shifts the histogram to the black end. All shades of grey have 20 subtracted from them. Values 0 to 20 “bottom out” at 0 and shadow detail is lost.

53 If you decrease the Brightness Decreasing the brightness by -20 shifts the histogram to the black end. All shades of grey have 20 subtracted from them. Values 0 to 20 “bottom out” at 0 and shadow detail is lost.

54 Increasing Contrast is equally destructive as both highlight and shadow detail can be lost.

55 Decreasing Contrast is safe but means that the gamut of the output (print or on screen) is less than perfect. The picture will have no pure blacks and no pure whites.

56 Curves – Shadow lift Anchor the head and tail at 255 and 0 respectively, merely redistributing the profile.

57 Curves – Shadow darken Anchor the head and tail at 255 and 0 respectively, merely redistributing the profile.

58 Photoshop 2 Quality Example Excellent Shadow detail Excellent Highlight detail Excellent Colour Purity

59 Photoshop 2 Auto Contrast Loss of Shadow detail Loss of Highlight detail Posterisation in bland areas with shallow gradation Gross Exaggeration – limits set to 10%

60 Photoshop 2 Increase Saturation Loss of Colour Purity Gross Exaggeration – Colour +50

61 Photoshop 3 Never Modify a layer, except perhaps for cloning, healing, sharpening, blurring Always Add modification layers and adjust blending modes

62 Saving Never save using a “Lossy” compression method Use PSD preferred as preserves all Layer information or Tiff, lossless compression CD’s are relatively cheap so save generations to CD

63 Saving 5MPx: RAW 2592x bit colour, 2.29Mb on card expands to 28.8Mb in Photoshop

64 Saving 5MPx: HQ(JPEG) 2288x bit colour, 2.1Mb on card expands to 11.2Mb in Photoshop

65 and Finally.... Enjoy The rewards can be worth it. Philip and Janet


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