Digital Photo Printing - a technical assessment

by W.A. Steer PhD
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Following the rapid take-up of digital cameras and digital photography, consumer in-store and online digital photo printing services have become widely available. Being interested in photography and imaging systems, I generated a series of photographs and test-images to evaluate the services available from a technical perspective. I got the files printed at several stores, and my findings are presented here.

Introduction

I only recently became aware that it was possible to get proper photographic prints made from digital image-files as a consumer-priced service. Basically, the customer provides digital image files in common formats such as JPG, BMP, or TIFF, typically on CD or memory-card for a shop, and the service 'prints' those images onto traditional photographic paper in the familiar 6×4", 7×5" etc. sizes. Compared to home ink-jet prints, pictures on photographic paper tend to look much 'richer', and are vastly more durable with regard to handling by sweaty fingers, humid environments, and fading in daylight.

I was intrigued to find out more about this digital printing service, and whether it could give me a way to obtain prints over which I had a high degree of control of the colour and contrast. Given my long-standing (and now professional) interest in technology, imaging, image-processing, and more recently colour-science, I was keen to put the new facilities through their paces. Would this tool be useful to me in future?

Jessops is a nationwide chain of photographic shops (in the UK), with a reputation for serving the higher end of the amateur market. I've been taking my regular 35mm films to them for C41 D&P for many years now, and had reasonably consistent and satisfactory results. I had high hopes for their digital printing service, though tempered by a healthy cynicism. After all, I've been going out of my way to get my photographic negatives sent off-site for 'optical' printing recently, to avoid digital aliassing (jaggies) in my conventional prints!

Jessops use Fuji Frontier printing equipment which has a native 300dpi resolution (so a 6×4" print contains a nominal 1800×1200 pixels). To retain maximum sharpness, particularly from computer-generated imagery, I was hoping to obtain 1:1 mapping of pixels in my image to pixels on the paper. It became apparent that that would not be a standard option for a consumer service! Could I establish, by experiment, the perfect source image pixel dimensions to contrive a 1:1 mapping anyway?

Test images

So, with all these ideas in mind, I devised a set of test-images to enable me to evaluate the technology. I wrote a data CD with several high-quality scans of 6×4" traditional colour prints, a couple of black-and-white subjects (scanned from colour-prints), some basic colour and greyscale gradations put together using PaintShopPro, a chromaticity diagram (more information later) which reproduces the full colour-space of sRGB (ie standard PC-graphics), and a couple of zoneplates (more information below) and carefully-constructed fine patterns of alternating black/white pixels and 'rulers' by which I could detect and measure any scaling processes. The previews below give a flavour of the spectrum of images I tried.

1 - Zoneplate and rulers 2 - Colour gradations 3 - Chromaticity diagram and greyscale

1800×1200 TIF
Measures scaling and resolution 1800×1200 TIF
Gauges gamma interpretation 1800×1200 BMP
Gauges gamut and colour reproduction,
strict sRGB coding

4 5 6

1800×1200 BMP
Gauges best scanner gamma value to use 1800×1200 TIF
Overall 'photographic' quality 1171×795 JPG (175kB)
Overall quality, in predominantly dark scene.
Sub-native resolution; arbitrary scaling.

7 8 9

1800×1200 TIF
Overall value for black-and-white imagery 800×531 BMP
Simulated colour-spectrum graphic,
in strict sRGB coding 1800×1200 TIF
A useful greyscale chart

Initially I was very impressed with the results from my local Jessops, though I remained disappointed by the hints from the scaling-tests that 1:1 mapping may be actually impossible owing to their software-configuration.

While pondering the results I thought it might be interesting to take the images around to some of the other high-street photo-outfits. It is generally recognised that the results you get from conventional developing and printing vary considerably from shop to shop, although it's not very practical to do scientific like-for-like comparisions. Does 'digital' level the field? I rather guessed not, but it's easy and relatively cheap to take a CD of test images round to many shops, providing identical source material to all, to see how they fare. I fully expected that Jessops would prove superior to the supermarket or drugstore offerings, and while-you-wait station/airport/mall slot-machine kiosks, but were my prejudices warranted?

The Shops

Jessops, Crawley

The Crawley branch of Jessops has a front-of-shop serve-yourself kiosk into which you put your CD or memory card and select the photos you want printed and their sizes. Having completed your order the machine issues a ticket for you to take to the counter and pay. Your photos are then queued for printing on the Fuji Frontier equipment behind the counter. Photos are available in several sizes from 6×4" to 9×6".

Example prices: for 5 or more 6×4" prints; 1hr/24hr 20p/25p per print
Equipment: Fuji Frontier 355, 300dpi laser, Fuji Crystal Archive paper. "Pixology" front-of-shop input-kiosk.
Filetypes accepted: JPG, BMP, TIFF (first 20-odd letters of filename shown)

Boots, Crawley

Apparently you can have digital prints made behind-the-counter, but there's no obvious way of selecting which images you want, so it's probably an all-or-nothing affair. Instead, I tested the front-of-counter serve-yourself Kodak Digital Photomaker kiosk service. Again you insert your CD or memory card, get a graphical preview of your images, and use the touch-screen to select them. Unfortunately the machine does not show any part of the filename or the pixel size of the image, so you're in trouble if you have several different but similar-looking pictures. 6×4" prints appear in a minute of so, and when you're done, you take them to the counter to pay. The machine has frequent American-accent voice-prompts, which I found extremely irritating! These were the most expensive prints tried!

Example prices: (while-you-wait) 49p per 6x4" for up to 19 prints, 39p for 20-49, 29p for 50+
Equipment: Kodak Digital Photomaker (stand-alone kiosk), 300dpi thermal?, Kodak xtralife paper (matt finish)
Filetypes accepted: JPG, BMP, TIFF (no filename or resolution shown)

PhotoMe stand-alone machine, Gatwick Airport

This machine is very similar in concept to the Kodak Photomaker, except that it is coin-operated. There's no minimum order, and all 6×4" prints are 20p each.

Example prices: while-u-wait c.1min 20p per 6x4"; no minimum order
Equipment: PhotoMe kiosk, 692dpi "3rd generation thermal printer", unbranded "PhotoMe" postcard paper
Filetypes accepted: JPG, BMP only [no TIFFs]

Tesco, Gatwick/Horley out-of-town

This is an over-the-counter service. For simplicity they really expect to take your digital media and print one of each image for you. When they're not busy, you can pick and choose which images you want on their behind-the-counter screen. You also get a free index print (showing original filenames) with each order.

Example prices: 1hr 15p per 6x4" print; get an index print (shows original filenames) free with order
Equipment: Gretag MasterFlex D1008 ?254dpi ?HRCRT, Kodak paper
Filetypes accepted:"we take most formats - we'll soon let you know if we can't read it!" (JPG, BMP, TIFF, +?)

For reasons of economy not all images were tested on all printers.

Results

Results summary

Unsurprisingly from this sample, Jessops came out top. Neutral greys, nice full contrast range, colours which are a remarkably good match to my screen. Test-patterns reveal that the Fuji Frontier is a very capable printing engine; the one in this store is less than 6 months old, and evidently well-maintained. I'm still disappointed in the two-stage resampling/scaling in the digital chain of Jessops' setup, which causes an extra stage of blurring as well as ruling out any hope of 1:1 pixel prints. Revisiting Jessops 8 days later produced a second set of prints indistinguishable from the first set, so reproducablity looks good.

Both the Boots (Kodak Digital Photomaker) and PhotoMe stand-alone kiosks are clearly in a lower class than a full-blown (behind-the-counter) mini-lab machine. They both showed marked greeny colour-casts, and gave marginally sharper photographs than Jessop's setup, but their cruder scaling algorithms result in 'crinkly' diagonals and risk other aliassing artifacts.

Tesco's Gretag MasterFlex is a mini-lab machine, but lower resolution than the Fuji. The colour reproduction was fair, though the blacks were muddy, and images were the softest focussed of those tested. Its older technology and/or poorer maintainance and non-specialist operators may go some way to explaining its results.

Full results and images

For the full results, images, and detailed critique, please go on to the next page...

DETAILED RESULTS (next page) >>>

Created: February-March 2005
Last modified: 12 June 2005
Source: http://www.techmind.org/photoprinting/index.html

1 - Zoneplate and rulers	2 - Colour gradations	3 - Chromaticity diagram and greyscale

1800×1200 TIF Measures scaling and resolution	1800×1200 TIF Gauges gamma interpretation	1800×1200 BMP Gauges gamut and colour reproduction, strict sRGB coding

4	5	6

1800×1200 BMP Gauges best scanner gamma value to use	1800×1200 TIF Overall 'photographic' quality	1171×795 JPG (175kB) Overall quality, in predominantly dark scene. Sub-native resolution; arbitrary scaling.
7	8	9

1800×1200 TIF Overall value for black-and-white imagery	800×531 BMP Simulated colour-spectrum graphic, in strict sRGB coding	1800×1200 TIF A useful greyscale chart