Photo Stock Library

introduction

www.seafriends.org.nz/photolib/intro.htm
One of the big tasks before us is to bring the sea to the surface, to open windows to the sea so that everyone may enjoy its mysteries. On this site many colour photographs have been published in low resolution, photos that people can use personally and for education, but not in budgeted print runs. However, the medium- and high resolution formats are available at an affordable price. This page introduces you to digital pictures, JPEG compression, resolution, cost and how to order an pay for images. 

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Remember that underwater photography is extremely costly because of limited opportunities, unco-operative subjects, very difficult circumstances and a lot of equipment breakage, flooding and salt damage. Despite all this, many underwater photographers have risen to the challenge and have recorded precious events on film. These are now available immediately, by electronic means while at a reasonable cost.

Writers who write for magazines will find this site an almost inexhaustible source for articles to inform their readers about things that really matter to our lives and our futures. Within minutes they can uplift all the necessary researched information they need and beautiful images as well. This section is about those images.
 

E-mail us with your requirements. Very often we have more images that may better suit your requirements.
For more information about underwater photography, read our essential course www.seafriends.org.nz/phgraph/index.htm
 
 

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Electronic pictures
Almost all pictures shown on this site are available as high quality photos. Exceptions are many line drawings which had to remain compact, but even these are available in high resolution. Each photo is identified by a letter (the author's identity) and six digits as shown on the small thumbnail pictures with the white margin underneath. When clicking on a thumbnail, the low resolution picture of 450 by 300 pixels may be shown. This low resolution format can be used freely for schools and making overhead slides or even for publishing as small images. The medium resolution (900x600 pixels) and high resolution (3000x2000 pixels) images are not stored on the web site but are available by e-mail.

All pictures are in the sRGB (Red Green Blue) colour scheme, which is the most standardised available. Printers/publishers will convert these to a CMYK (Cyan Magenta Yellow blacK) colour scheme of which there are many. We have taken care to make the pictures look on screen what they should look like in print, yet providing the full dynamic range of light intensity. But there is room for interpretation. The quality of the light under water is highly variable and so are the colours seen in underwater pictures. To complicate matters further, although divers experience the underwater world as a sea of light and brilliance, most pictures in print appear much darker and more contrasty, showing either completely dark backgrounds or at least not what the sea really looks like.

Note! the images on the web may not have been graded correctly.
Ask for a graded 'comping' image of 450x300 pixels, as these images print correctly.

All low resolution pictures on Internet have been compressed using JPEG image compression of factor 40, which in our judgement, is an acceptable compromise between size and quality for printing or viewing on the web. On this page you will find samples of these pictures, for you to judge. All pictures have been tidied up and cropped where necessary, but sharpness has not been pushed to extremes.

Our medium resolution format is a screen-sized picture of 900x600 pixels (or 800x600 in screensavers), which prints to 4.5x3" (postcard) at 200ppi or 3x2" (business card) at 300ppi. This quality is enough for postcard sized images.

Our high resolution format is 4050x2700 and 3000x2000 dpi or 375x250mm @ 200ppi or 270ppi at sub-A3 size. It is saved in JPEG as a 3-9MB file, which can be sent by e-mail.


 
JPEG compression guidelines
The sRGB colour space allows images to be compressed considerably although with some loss to quality when this is pushed to extremes. Here follows a guideline showing compression rate and actual file size compression, together with the kind of quality loss caused. Note that JPEG compression does not result in predictable file sizes as busy and noisy images require larger files than monotonous blurred ones.
Rate * file size Losses showing
10 20-30% No visible losses. This compaction rate is suitable for fine print.
20 8-20% Losses begin to show, particularly on sharp boundaries, but this compaction is acceptable for your photo album of snapshots, as losses do not show in print.
40 4-8% The losses begin to show in print, although seen with difficulty and only to the very alert observer. Not suitable for filing but very suitable for slide shows and screen sized images, comping and high quality internet files.
80 2-4% The losses and artefacts begin to show on screen. This is the highest compaction one can do for small internet files. All photos shown on our web site are of this quality. In smoothly grading colours, steps or bands may become visible. Note that a small image is much more affected than large images.
160 0.8-2% This very compact file can occasionally be used but artefacts and losses are clearly visible. Still, it is amazing how well it works for large files. Don't use it for small files.
* the compression rate is a number between 0 and 255.
Please note that large files can be compressed much more than small ones.

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Resolution
The required image size or finenes or resolution is often poorly understood, by photographers and publishers alike. Often a 30MB file is requested for an A6 (quarter page) reproduction. Publishers and printers confuse their equipment's ultimate fineness of 600-1200lpi (lines per inch) for sharpness in letterprint, with what the eye can perceive in a raster image in pixels per inch (ppi). Note that in the discussions on this page, we use dpi as meaning ppi.

When printing sharp text, a high resolution is required to prevent the steps in slanting lines and curves (alias) but the human eye cannot perceive this in photographic images. We must not forget that the sharpest of lenses do no better than 100 lines per mm on film and that most films can only just match this. Thus the maximal resolution of a 35mm image is around 36x100= 3600 lines horizontally, just visible. It can be exceeded only by having better optics, using small apertures and the finest of films. Alas this is not possible for most real-world situations. In order to produce 3000 'lines', one must have at least one light pixel alternated by one dark pixel in a 3000x2000 pixel image. Clearly, 3600 lines is not readily attainable in a 35mm original.

Art magazines pride themselves in producing sharp images at 300 dpi, but much of this is negated by uncertainties in paper alignment during printing. Fortunately a small amount of misalignment produces a false sense of sharpness. Note that by far most magazines do no better than 200 dpi and that newspapers are limited to 100 dpi. To standardise our discussion on sharpness and resolution, I have produced the table below, all relating to fine art print at 300 dpi. Note that each step corresponds roughly to a factor 1.5 (in fact the square root of 2 = 1.414). By this measure, A4@300dpi quality can be attained only with willing subjects, much light and a good primary lens (not a zoom lens). Most of my own photographs do not quite make it and rate A5 instead. However where these are good A5s, I retain the larger image size. Note that most commercial scanners produce 3000x2000 pixels (Kodak) but an in-house Nikon Coolscan 4ED does about 4050x2700 on a 2870 pixel CCD.

Note that an A5 quality defined this way can quite happily be enlarged to A4 and even A3, as most photographs in print are not much better and the image is viewed from further away. Note also that those produced with large format cameras (45x60mm, 60x60mm) are often preferred for full page photographs. Also note that A4@200dpi is identical to A5@300dpi.
frame size mm inch image size pix image size MB file size
A4 full page 300x210 12x8 3600x2400 26 MB 4-9MB
A5 half page 210x150 8x6 2400x1800 13 MB 1.5-3MB
A6 quarter page 150x100 6x4 1800x1200 6.5MB 0.8-1.5MB
A7 eighth page  100x75 4x3 1200x900 3 MB 0.4-0.8MB
A8 'business card' 75x50 3x2 900x600 1.5MB 0.2-0.4MB
Screen size 800x600 1.5MB 0.1-0.2MB*
All above values at art quality 300 dpi; normal magazine print quality is 200 dpi.
Normal scanner resolution for 35mm is 3000x2000 pix. High res 4200x2800 pix.
* compressed further, visually acceptable as slide show or for comping.


 
What it costs
Your payment helps underwater photographers and the Seafriends movement. Half goes to the photographer and the other half goes to the Seafriends Foundation, which pays for the costs of administration, keeping, handling and mailing. So in a way, you will be supporting many good things!

Low resolution images and thumbnails are free!

Medium resolution images (900x600 pixels) are US$ 105, sent by e-mail.

High resolution images are US$230, sent by e-mail.

A3-sized posters as described below are US$23, and this has been discontinued

Discounts for multiple images will be considered. Should you have problems with the above pricing, please let us know.

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Affordable posters
We've made posters affordable by printing our high resolution images electronically on a high quality ink jet printer with durable inks and paper. The A3 poster (300x420mm) has an outlined 375x250mm image with a few lines of text describing the situation. Schools and individuals will now be able to collect these wondrous images of the sea. Enquire first whether the photo of your choice has enough quality for this enlargement.

Other printed posters are now available:


 
How to pay
The only way to pay is using our account with PayPal, a very large Internet 'bank' (is in fact an 'escrow' agency). By clicking on a payment button below, you will be transferred to a secure PayPal server where you are asked to enter you credit card details. These will remain unknown to us but PayPal sends us confirmation of your payment by e-mail. We will then dispatch your order to the address provided by yourself. Please note that all prices are in US dollars. In the info box, mention the image's filename (like f012345) and additional information (up to 80 characters). Better still, send us an email. Use the Universal Currency Converter to calculate the price in your own currency.
 
 
info:The preferred option for standard A3 posters.
info:One medium-resolution 900x600 pix image by e-mail.
info:One high-resolution image of 3000x2000 pix or higher.
Your variable payment amount US$: 
Optional message/info:
Press the donate button to pay your photo order. Ships usually within a few days.
Did you know that the Seafriends CD contains all the 5000+ small images on this web site and in addition over 2000 medium resolution images (800x600 pixels typically) from which you can quickly make a selection? Follow this link to order: buyCD.htm.

Payment by PayPal is now the only way you can pay. We had to discontinue sending out invoices because too many 'reputable' publishing companies failed to pay. However, you will receive an invoice by e-mail with a description of the images sent to you, an assurance that we are the owners of those images, and a stipulation for what you are entitled to use these. The invoice is also a receipt of payment.

We like to hear back from you, so please stay in touch.

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