Computer requirements for image capture


Image capture for use in digital work can be performed in several ways, firstly there is the use of a scanner. The earliest of these were drum scanners. These require the original to be mounted within an acrylic cylinder that rotates at high speed passing the image across an array of precision optics that pass the information to matched photomultiplyer tubes (PMT’s) corresponding to red, green and blue light. With the manufacture of cheap CCD and CSI flatbed scanners many see this technology as slightly arcaic but Drum scanners are still used in certain circumstances (mostly archival or extreme enlargement) for their extremely high resolutions and ability to wet mount originals.

The Howtek 4500 drum scanner and a close up showing a mounted image.

The difficulties in using a drum scanner are however significant. Not only is the hardware extremely expensive and only serviced by a few remaining companies most notably Aztek but many use SCSI interfaces prompting the need for seperate cards to facilitate use with modern PC’s. From a web design perspective they are pretty much redundant as the resolution obtained is far in excess of that needed for display.

Flatbed scanners

Flatbed scanners that first became affordable around the mid 1990’s can be divided into two types. Contact image Sensor (CIS) scanners use a range of red, blue and green LED’s that reflect light off the original that is then gathered by a sensor array. Charged Coupled Device (CCD) scanners use a light source, again refected off the original that is directed by mirrors to a sensor consisting of light capturing CCD elements. Both have advantages and disadvantages although CCD technology is generally recognised as having greater depth of field and signal noise ration and is used in the majority of modern flatbeds.

A comparison of CIS and CCD sensors.

Both technologies can scan transparencies with either built in units or removable reflective beds and slide mounts. Early models of both types used SCSI but these have been replaced with the faster USB 2.0 and firewire interfaces. One of the advantages of CIS along with smaller size and portability is that hardware can be powered directly via USB eliminating the need for an external power supply. The majority of flatbed scanners come bundled with driver software utilizing the TWAIN interface standard however there are several proprietry and third party software options for reparing and manipulating scanned images.

Interfaces from the EPSON scan utility on the left and CanoScan Toolbox on the right.

Canon provides the CanoScan Toolbox while Epson by default uses EPSON scan. Third party options include Lasersoft Imaging’s Silverfast software that now comes bundled with some Epson products and VueScan from Hamrick. Both cost a little extra but are often seen to provide a more quality result than the proprietry software.


Another way of capturing content is with screen grabs. On the PC you have several options the simplist of these is to ensure that what you want to capture is displayed on screen then hit the Print Scrn key. Then entire screen area will then be copied to the clibboard ready to be pasted into an image editing program for cropping and further manipulation. If you press the alt key in combination with Print Scrn you will copy the currently selected window. Windows 7 also includes the snipping tool. This allows you to select only small portions of the screen to capture, you can then write over this with the pen tool or highlight areas before saving to a variety of formats.

A fullscreen grab using PrintScrn on Windows 7 and a selected window grab using ALT - PrintScrn.

With Mac OSx there are several more options for screen grabs. Pressing Command – Shift – 3 will take a screenshot of the entire screen and save it to desktop. Pressing Command – Shift – 4 then selecting an area will take a screenshot of an area and save it to desktop. Pressing Command – Shift – 4 then clicking on a window will take a screenshot of the selected window and save it to desktop. You can also include the control button in any of the above combinations to copy the area in question to the clipboard. Mac OSX also has a screen grab application like the snipping tool called Grab, this will capture entire screen or screen selections and allows you to set a timer before any image is captured.

Single lens reflex cameras

The camera market is filled with potential options for capturing images from scratch. 35mm SLR cameras are now extremely cheap thanks to the explosion of digital options. However the need for processing then scanning of images takes time and adds expense to a web design workflow. Digital SLR’s use the same principles as earlier 35mm cameras using a relex mirror to direct light to the eyepiece via matte focusing screen and condensing lense. When an image is captured the mirror swings upwards allowing the image to be projected on a sensor. The sensors used vary greatly and can use either charged coupled device or complemetary metal oxide semiconductor (CMOS) technology. The size of the sensor also varies ranging from the full frame 24x36mm sensors seen in models like the Canon EOS- 1D and the Nikon D3 to the four thirds system (26 percent of full frame) used in many Olympus models.

A comparison of various CMOS sensor sizes including the four thirds system used in many bridge cameras.

A size comparison of various

Sensor size is important to consider when choosing a DSLR as smaller sensor sizes can lead to a reduced depth of field, high crop factor and lower dynamic range. The main advantage of a DSLR is the availablitlity of a large range of lenses allowing for more creative control over the subject when shooting. Depth of field can be manipulated to a greater extent especialy using wide aperture/angle lenses unavailable to compact cameras. Telephoto and macro options also allow a greater variety in the treatment of subjects. Another advantage of DSLR’s is that many allow you to shoot in RAW. Although the file size and reolution are far too large for use of the web this format still allows a greater degree of image manipulation without image degredation but can then be saved as any file format the photograher requires as opposed to many compact digital cameras that shoot only in lossy JPEG. DSLR’s also provide higher quality under low light and less delay when taking shots making them better for capturing fast moving subjects.

Compact Cameras

Compact cameras are generaly cheaper a lot more protable and easier to use than DSLR’s. They lack the reflex viewing system with shot being composed through an LCD screen and have smaller sensors than DSLR’s with a diagonal of around 6 mm coresponding to a crop factor of 6. This translates into weaker low light performance and greater overal depth of field.

Compact cameras - The Panasonic Lumix FS35 and the Sony Cyber-shot WX7

Designed for novice photographers, compacts feature a huge array of automated functions to increase image quality. The Panasonic Lumix DMC-ZX3 for example features intelligent resolution, High Dynamic mode, Digital red eye removal, AF tracking, Face recognition (with baby mode that proritises exposure and AF on any subject in frame thats registered as under 3 years of age!) anti shake and intelligent ISO selection. Compacts therefore allow the creation of high quality images without as much investment as a DSLR and without the inconvenience of lugging around a seperate bag of lenses. Advancements such as lossless digital zoom also increase the focal range that many compacts are capable of.

Bridge cameras - The Fujifilm FinePix HS10 and S8100fd

More recently the introduction of bridge cameras that feature four thirds sensors and interchanchable lenses along with the advanced image processing features of a compact are beggining to blur the line between point and shoots and DSLR’s. Many mid to high end compacts are now supporting RAW format making them an even more attractive proposition. All digital cameras support connectivity via USB 2.0 there is however a prolifferation of proprietry connectors that only fit certain brands of camera. Certain DSLR’s and compact cameras are now supporting WI FI both for transmission of images to a hard disk or PC for storage and for control via PC/Mac or in some cases from smartphones. Most cameras are bundled with proprietary software for achiving, file handling and basic image manipulation. Nikon has its software suite for coolpix for example, Canon similarly provides the EOS utility suite for its products.


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