Additive primary colours consist of red, green and blue - abbreviated to RGB. RGB is a colour mode that is used for on screen purposes. Additive colour systems work by adding varying amounts of the three primary colours onto a black background, black is the absence of light and so colour is added to a screen by adding light. In this case my adding equal amounts of the three colours you achieve white. It is also possible to create secondary colours, by varying the amount of the primary colours two colours can be used to create cyan, magenta and yellow.
Subtractive primary colours consist of cyan (C), magenta (M), yellow (Y) and black (K) – known as CMYK. These colours are the same as the secondary colours created in the RGB colour system. Subtracted colours are based on the process of light reflecting from an object and so works rather differently to the RGB system. In the subtractive system instead of beginning with black, you begin with white and the three primary colours (CMYK) are subtracted from the white to create the colour. The secondary colours for this system are red, blue and green, the same as the primary colours of the additive system. CMYK colours are generally used for printing; this is because in most instances you begin with a white page that reflects RGB light. Combinations of cyan, magenta and yellow are used to filter out the RGB wavelength and the use of the black ink gives a more substantial black than what you would find with just a combination of the primary colours.
The conversion of RGB to CMYK is a very common process, as a photograph taken on any camera will come in its RAW format as an RGB file. The camera will interpret colours by assigning each pixel a red a green and a blue value, so that the file can be previewed on the camera screen. It is only when you convert the files colour mode that it can become CMYK. By doing this, Photoshop, for example, will give each pixel a new colour value comprising of a cyan, magenta, yellow and black value. As you can imagine, each image with say 3000 pixels now consists of more data than what it had originally, increasing the file size ever so slightly.
After converting the colour mode of an image or a document it is important that you consider what effects occur from this change. Some RGB colours will be out of the CMYK colour gamut and so will look completely different from the RGB version. This is because the RGB colour mode has a much wider colour range than CMYK and when converting particularly bright colours they lose their intensity. When proofing colours for print you should send a proof to the client with a CMYK colour mode so that they can view colours accurately for how they will be printed. If the client agrees that there might be a problem with the converted colour you can tweak this in pre production stages before printing. Perhaps by changing the CMYK values you can try and find a colour that is more representative of the original. When printing, particularly if you are concerned with the colours, you should print out a small version or a cropped section of the area of concern and view this in comparison with other printed materials with this colour.
Another aspect to consider when editing an image is 8 and 16 bit colour modes. As I have mentioned before, using different ratios of red, green and blue allow us to make a whole range of different colours on screen. However, to work out the exact amount of colour possibilities in a given mode we can use this formula. Bit means two - so when working in an 8-bit mode, to work out how many shades you have for each colour, you use the calculation 2 to the power of 8 - 2x2x2x2x2x2x2x2. This is equal to 256; you have 256 different shades of red, 256 shades of green and 256 shades of blue, which will allow you to create up to 16.8 million different colours. For 16 bit, this figure is much larger, which means that the tonal range is much greater. For 16 bit, you use 2 to the power of 16 - 2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2 which then gives us 281 trillion possible colours with 65,536 shades of red, green and blue. The human eye can see as high as 10 million different colours so these colour modes are indistinguishable to us. We can’t even see all of the colours available in the 8-bit mode, so really the use of 16-bit only becomes useful when editing an image.
If your camera is capable of capturing RAW files, it can capture images in a 16-bit mode. Most common digital cameras cannot do this as they store images as JPEGs. JPEGs do not support the format of 16 bit so when printing or converting to JPEG you tend to lose the colour capability that 16 bit gives us. Essentially, by using a 16-bit colour mode we have a lot more flexibility when editing our image. The tonal range is much greater than 8 bit and also the editing is a lot less damaging to the image, Photoshop can expand and reduce the range with ease and without risk of colour banding that you may get in an 8 bit image pushed too far. A drawback to using 16-bit is that the file size is much larger than using 8 bit and also you cannot JPEG it without losing the colour capabilities. One possible solution could be to save a 16-bit version where you can edit it as much as you like, but also save an 8 bit version that can be used for printing and general workings.
There are many different types of colour profiles that will affect the appearance of images that you open. All images will have an embedded colour profile that is assigned by either the camera or the editing software that it is opened in. For example, on my Mac computer I have ‘Adobe RGB’ set as my RGB space and ‘Coated FOGRA27’ as my CMYK space. It is important to keep these profiles consistent for different purposes, for design and artworking the above settings are fine but for web or for printing it may be customary to use another setting that is more reflective of the circumstances. In Photoshop there is an option to notify you whenever you open an image that does not match your colour space and whether you would like to change it to your settings or keep it as they were. Again depending on circumstances I decide whether to change or keep it as the image comes. For example, the other week I had to open a Photoshop document that had been created by our web designer. He had obviously set his own colour spaces on his own computer and when I opened the file on my computer I was careful to keep it at the same colour mode as it was originally so that it still matched other files on the website. When converting files in Photoshop, for example an RGB image to CMYK, Photoshop will automatically assign my chosen CMYK profile to the image. At moments like these, it can be useful to save the image as another version, named obviously to indicate that they have a new colour profile. This way you are able to keep all of the original colour information in case you need to refer back to it at any point.
Overall the management of colour in editing suites such as Photoshop is extremely important when creating final artwork for reproduction. Test prints may need to be done in order to get an accurate representation of colours and it may also be advisable to compare the colours with what has been produced before - particularly with branding and logo colours. A methodical workflow that is adopted by all should be in place and this will hopefully allow for reliability and consistencies when producing materials. By setting the same colour profiles where needed and by keeping logs of any changes to colour modes this means that when doing reproductions of previous work we can keep it as similar as possible when printing.
When creating artwork for different sources any images used in that artwork must be at a particular resolution in order to use them with full impact and sharpness. If for example, you are intending to create an A4 sized brochure and you wanted the front cover to feature a full sized image that covers the whole page, there are a few matters to consider in terms of resolution. Upon opening your image in Photoshop, firstly you should check what the actual resolution is, the dpi (dots per inch) as it is referred to. For Litho or digital printing the resolution must be 300dpi in order for it to print at maximum quality. For large format printing you can print with a dpi as low as 100, although it does depend on the printer, and for web a resolution of 72dpi is standard procedure. Most images that you take yourself or images that you buy at full size will be 300dpi. So once you have checked this, you can consider the actual pixel dimension of your image in comparison with the space you would like it to fill. Pixel dimensions refer to how many actual pixels are in your image and relating to this, what size in millimetres your image can be taken to before it starts to blur. In my example, we are working with A4, we know that our image must be at least 210mm wide and 297mm high, if you are allowing for bleed as well, then it is better to work to more than the desired size. This process is relevant to all different sources and purposes, you must consider the space that your image must fill, the resolution it will need to be and whether your image meets the requirements. Images can of course be scaled up or down in proportion to the dpi or pixel dimension, but it is also possible to resize an image and increase the amount of pixels if you need to. Although this can cause ‘Jpegging’ where you get a blurry noticeable jagged edge to the pixels as Photoshop is simply trying to guess what pixel may fit in-between the existing pixels.
When printing an image it is vital to consider the pixel dimensions and also the colour mode of our image. Most images will start off by being in RGB mode that is used predominantly for web or video use. When creating artwork for print it is customary to use the CMYK colour mode that will give accurate representations of how the colour will actually print. To use CMYK in a web environment may cause problems with how the browser interprets the colour, similarly, to use RGB in print may mean that colours are printed very differently to what appears on screen and may not be read well by printers. The pixel dimensions and resolution of an image also have a great effect on how an image will be presented. There are different requirements of resolution depending on the application. 72dpi is usually required to create high quality images on the web or on screen, the pixel dimension of the image should be either larger or equal to what the space requires. You couldn’t take a 300 pixel wide image and stretch it on screen to 900px wide without the sharpness of the image being sacrificed. Pixel dimensions should be altered to fit the space, whether it be reducing the size or increasing it. When it comes to print media, there are many different options that will require different resolutions from an image. Litho, or digital printing is used for things like brochures and business cards. In this case, the resolution should be full 300dpi and similarly to web, you wouldn’t take a 200mm wide image and place it full size on an A4 brochure. Another type of printing is large format printing, this allows for more flexibility than Litho or digital printing and usually the resolution of an image will be no more than 150dpi. However, the resolution in large format printing does depend on the image that you are supplied. An image of a cloud, which is quite soft without any hard edges, may be printed at a much lower resolution because you do not have to worry about any hard edges that might blur. But if there was a plane, or a bird used in the same image, reducing the resolution down to say 50dpi, would mean that the hard edges on the plane would be very pixelated and not very detailed at all. Producing high quality images is all about knowing the intended purpose and the methods of producing the image.
The limitations of using a low-resolution image at 72dpi is that the image can only be used in a print format at a very small size. For example, if you had a 200mm x 200mm image at 72dpi, you can change the dpi proportionately (without resizing it) to 300dpi. BUT the pixel dimension will now only be 48mm x 48mm as you are not adding any pixels, you are only changing the resolution they will be viewed at. This image will not go any larger than 48mm by 48mm without suffering from artefacts created by stretching. Stretching the image may mean it could lose sharpness, lose detail, look blurry with noise and if not done properly it could effect the aspect ratio and make it incorrect. Stretching images particularly affects text on an image, as text always features very sharp and straight lines, and these could end up having steps in them if the image is stretched too uncomfortably.
The file size of an image is usually dependant on a few different factors - the total number of pixels, the resolution and the bit size. There is a particular formula for working out file size which is as follows: file size = (height x width x bit depth x dpi squared) / 8. Another factor which effects file size is the format, categorised as compressed and uncompressed. A compressed file would be a flat JPEG, convenient, as a JPEG is small in size and compatible with most hardware and software. Uncompressed would refer to a RAW camera file or potentially a TIFF. A TIFF file still contains all of the raw data from the camera and is usually much larger than a JPEG. As I mentioned before it is possible to change the dpi or resolution of an image without adding any more pixels and effectively changing the file size. If you increase the resolution, the pixel dimensions will usually be decreased, where as if you increase the dimensions of the image than the resolution will decrease. The dimensions of the image will affect the print size of the image. If you reduced a 300dpi image to 150dpi it can be printed much larger than if you were increasing a 72dpi image to 150dpi.
Bit modes also have a large affect on file size; an 8 bit mode, as mentioned before stores 256 different possibilities for both red, green and blue, where as a 16 bit mode will store 256 times more options for the three different colour channels. This does have a massive impact on the size of the file, it is at least double the size of an 8-bit mode and it can run much slower on a computer. Also considering that JPEG does not support the 16 bit mode you will always have to save your 16 bit colour images as either TIFFs or PSDs which are already much larger than JPEGs before you even consider which colour mode they have. 8 bit modes are a bit more flexible when it comes to file size, not only do they contain less data but you can also save them as a high quality JPEGs and keep that rather than the large TIFF files which are most of the time unnecessary.
When you save an image as a JPEG it automatically divides the image into a grid system. It will sort the pixels into blocks of 64, with 8x8 pixels in each block. The way that this works is that Photoshop, or whatever programme you are using, will discard any information it deems unnecessary. So if you had two pixels sitting next to each other in a full sized image that are similar in colour, Photoshop will discard one of the pixel’s colour info and it will become the same colour as the first. However, the more complex the image the less tolerance the image will have to compression. Looking at the box below, let’s pretend that we’ve got an image with an orange gradient. If you were to zoom in on the gradient, you would eventually see rows of small square pixels each with a different shade of orange. Now below, ‘A’ would fade to ‘B’ that would then fade to ‘C’. If you were to Jpeg this image, let’s say that Photoshop would deem square ‘B’ as unnecessary. There is a much clearer definitive line between ‘A’ and ‘C’ than when you’ve got ‘B’ in the middle. Simply, this represents what happens to colours and gradients during the JPEGGING process. The colours begin to have steps in them and the more complex range of colours you have the more steps in gentle graduations and images you will have.Now by storing the pixels in this 64-pixel grid format you are dramatically reducing the file size. As I have mentioned before, one single pixel will have a red, a green and a blue colour value, not to mention a value that determines its position and it’s resolution. By reducing the number of pixels that are in the image you are reducing the amount of information that the file has to keep in order for the image to appear as it does. By converting an image to a high resolution JPEG you can reduce the amount of pixels without massively affecting the appearance of the image. It is only when the image is repeatedly saved as a JPEG that any unwanted artefacts start to appear. Saving JPEGs does come with many different options that determine the size and the quality of your image. The lower the quality of the JPEG the smaller the file will be, as this will reduce the number of pixels, in contrast the higher the quality the larger the file will be as this is keeping more information. It is usually recommended to save JPEGs at their maximum quality and if you wish to reduce the size of the file, you can manually resize the image to a smaller dimension.
It is important to use metadata when capturing images, it has many advantages and although it can be time consuming entering the information for each image it can be worthwhile when reviewing them later. Technical metadata is information that is automatically assigned to an image by the camera; it includes details such as the camera make or model, the shutter speed, the lens used, whether flash was used and much more. Metadata can also be added to the image at a later stage on a computer, known as descriptive metadata. You can add keywords to an image that describe the subject or the location; you can add the name of the photographer and even a copyright status if necessary. Adding keywords can prove particularly useful as you can search for images this way, any terms that you add to the image are now searchable, so if you’re looking for a particular image out of an image library you can simply search the term most relevant. Technical metadata is also useful as it allows you to look back at images and decide which camera settings were particularly effective, you can evaluate the information stored in an image and decide which techniques were most effective and which you would use again in a particular scenario. Keeping this information accurate and up to date is a great way of keeping track of settings used in a shoot and also allows the opportunity to include your name and copyright status in the images without comprising the image.
Using the appropriate equipment for the right situation is very important. Beginning of course with the hardware, for a professional photography shoot where the images must be of high quality and style an SLR camera is usually appropriate. Cameras like these capture RAW files that can be manipulated extensively without compromising the quality of the image. A digital camera may be more suitable for web purposes or casual photos, it produces compressed JPEGs that can be printed immediately or saved for editing later. If you are reproducing an image that you do not have as a digital copy, using a flatbed scanner is most appropriate, as it will scan an image in the highest quality available. Once you have retained your images, software choices are also very important. When working with vector files for instance, it is advised that you use a vector-based programme such as Adobe Illustrator to edit the file, as it will keep the file in a vector format rather than converting it to a bitmap file. Vectors work without pixels and so can be stretched to any size without losing their quality. They consist of paths that create shapes and can be created and amended with the pen and selection tools. Bitmap files such as JPEGs or TIFF files are restrained to the size that they are captured at, and so it is best to edit them using programmes such as Photoshop where you can change both the appearance of the image and also the size of it. Programmes such as Photoshop also allow for changing and adding to the metadata of an image, and you also have many different options for file format when exporting the image. The format of the file will also determine the use of it. A JPEG is a flexible in the sense that it can be used for both print and web, although the size of the JPEG is what determines how large it can be viewed in both of these medias. An EPS file, or a vector-based file technically speaking, will not be appropriate for web as it has to be given pixel dimensions to be viewed on a website. Vector files can be printed although not directly, usually through a design programme such as InDesign where a final PDF is sent for print. An EPS file is particularly used for logos as it has the ability to become any size without any unwanted artefacts.
There are many different file formats to choose from when it comes to dealing with images. 1. JPEG – generally JPEGs are low in size, but they do suffer from JPEG artefacts after they have been resaved too many times or if they have been stretched beyond their size.
2. TIFF – A tiff is an uncompressed file format and generally has a large file size. They are high quality and usually they are a format that comes after the RAW camera format.
3. RAW – This type of file is straight from the camera, large in size, full quality but with the flexibility in editing that doesn’t come with a TIFF. You can change things like the exposure and white balance without affecting the quality of the image.
4. EPS – This file is usually vector based, it means that the image is not made out of pixels like a JPEG but instead the image is made from paths and drawings. A photograph is never vector based but something like a logo with text and a drawing is vector-based and can stretch to any size necessary.
5. GIF – A GIF format is typically used for web. They are limited in colours but consequently they have a very small file size. GIFs support transparency so they are an ideal format for saving icons or symbols that you want to sit on a website with a background. GIF format also supports animation, and when loading they appear fuzzy at first but gradually get crisper as the page loads.
6. PNG – PNGs are slightly larger than JPEGs and usually they don’t lose quality like a JPEG would. They are still small compressed files and are generally used for web. They can also hold transparency like GIF, but it is argued that they accomplish this better as the image will almost blend and alter itself to fit with the background.
The most common file formats I come across are JPEGs, TIFFs and EPS. These are the formats that I use most often. For web, JPEG is a standard format that displays images at their best. TIFFs keep an image at their maximum quality however mostly I will always convert these to high resolution JPEGs that are smaller, even when working with them in print. EPS files are preferable for logos and illustrations when printing. They will display at any size and will never lose their sharpness.
Overall, in this essay I have talked in detail about colour modes, theories and also the saving and use of images in their desired medias. Images are of a sensitive nature and knowing their intended purpose and size in hindsight is always useful in capturing them and storing them.
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