Design and Photography

Why raw?

Raw images are digital images in pure form. Minimal processing has been performed to convert the pixel information into digital format. The colours have not been assigned, no white balance adjustments have been performed and no tonal curve has been applied. In order for raw converters to read the file data the pixels must be coverted to digital, so minimal processing has occurred. In raw files the white balance and tonal curve is handled by the raw converter. Sharpening can occur in either the raw converter or other image editing software such as photoshop. You can reconvert the image as many times as you wish with different settings and there will be no degradation of image quality as the raw image is never changed. Every time a conversion is performed a new file is created .

JPEG images have been processed as much as the raw images with additional adjustments made using the software on the camera. Firstly the colours are assigned, meaning a colour is calculated for each pixel and a colour value is assigned to that pixel. Then white balance adjustments are made, tonal and other adjustments are made, some sharpening is applied then the image is compressed. The disadvantage with JPEG images is that if the automatic adjustments made to the image by the software is not quite what you were after you can’t undo what has already been done by the camera. The image you have to work with in software such as photoshop will be the compressed image. The sharpening and compression done by the camera software is irreversible.. Any adjustments you make to the JPEG will cause some degradation of the image. Another disadvantage is you will be unable to retrieve any loss of detail in the shadows that has occurred during the tonal curve that was applied when processing the image with the camera software.

The raw image which has had no adjustments made, allows the photographer to completely adjust the image according to the desired effect or what is required to improve the image. In order to have a good initial file to work with you would have to set your initial settings on the camera such as exposure appropriately according to the desired output .

Colour

Another advantage with raw is the range of possible colours. This is determined by the bits.

JPEG files are 8 bits which is equivalent to 256 levels of light intensity, meaning each pixel can render 256 different shades. This means there are 256 shades of each – red/green/blue – being 256 to the power of 3 which gives you 16,777,216 possible colours.

Applying this same formula to the Raw file, majority of raw files are 12 bit which is 2 to the power of 12 which gives you 4096 levels of shades per pixel. When applied to the red/green/blue it becomes 4096 to the power of 3 which gives you 68,719476,740 possible colours.

This can be explained further by looking at the dynamic range of the sensor. Dynamic range is the tonal distance from the darkest point at which a sensor holds detail, to the lightest point. Dynamic range is measured in stops of light. When light is increased by one stop, the amount of light is doubled and halved if going the other direction. In a camera with 5 stops, the shades that a sensor can rendor are spread across five stops, but not evenly. Pixels exposed to the full possible amount of light have reached their full capacity giving the image in total a possiblity of 256 shades in 8 bit JPEG images and 4096 shades in 12 bit raw images. As the exposure is reduced by one stop, the light is reduced by half therefore so are the availability of the possible shades. The possiblity of shades is distributed across all stops of light. At the point of highest exposure to light the maximum possiblity of shades is half , being 128 in 8 bit and 2048 in 12 bit. This represents the highlights of the image. At the next point of light exposure (going down) that 2048 is reduced by half again, becoming 64 shades in 8 bit and 1024 shades in 12 bit. This represents the Three quarter tones.

Across five stops this becomes – in 8 bit 128 – highlights, 64 – 3/4 tones, 32 – mid tones, 16 – 1/4 tones,16 – shadows, all adding up to the total of 256 possible shades. Applying this to 12 bit (raw images) it becomes, 2048 – highlights, 1024 – 3/4 tones, 512 – mid tones, 256 – quarter tones, and 256, shadows, again all adding up to the total of 4096 possible shades.

So, as raw processing leaves the data as 12 bits, the possiblity of colours, shades and detail is much greater than in an 8 bit JPEG. The JPEG file has fewer shades to choose from of each of the three colours to create detail than in the raw file.

Raw images allow for the photographer to customise the tonal curve applied to the image completely to optimise the image as desired. When an image is shot in JPEG format, the camera will burn the tonal curve applied by the camera software into the file, therefore you will be unable to reverse the curve and have to work with the current image as it is and edit it from there. It is also possible that the curve applied by the camera software when shot as a JPEG may have removed some of the detail in the shadows, highlights or both, depending on the type of curve that was applied. In raw, as long as the pixels have captured the detail, the settings can be adjusted in the raw converter therefore allowing you to keep the shadow and highlights in the detail of the image. In JPEG the application of a tonal curve can sometimes reduce the number of shades from 256having a degradation effect on the final image.

The advantage of the raw files over JPEG is that with raw files you have more shades to begin with before applying tonal curves and are less likely to loose the detail as opposed to a JPEG image that has less shades to begin with.

If processing a JPEG image the shades may become further apart with empty space creating gaps between colours resulting in a loss of detail and possibly creating banding in sections of the image with a low range of shades. In raw images this is not a problem as the larger number of possible shades causes them to be closer together.

As photoshop works in numbers and mathematical forumulas, when editing an image in photoshop it recalculates and determines new numbers. Sometimes the new numbers are not a whole number and will be rounded off to the nearest number. This results in lost data and degradation of the image and a reduction of shades. Sometimes two shades may round off to the same value and will therefore become one shade. As raw files have so many more shades, the distance between shades is larger and it is less likely that this would occur.

File size

Raw files are larger than JPEG files and therefore take up more room on your memory card and you won’t be able to take as many images as you would with a JPEG. Depending on the purpose of the images a JPEG image may be good enough. If you are generally taking raw images you would need to consider purchasing a larger memory card for the camera to enable you to take the same amount of shots.

Raw converter or camera converter

The camera’s CPU is much smaller and less powerful than the computer and has to process the image quickly when converted to JPEG. As the CPU of a computer is much more powerful, the quality of the conversion will be much more sophisticated in a raw converter and will be much higher providing more detail.

Compression

JPEG files are compressed, meaning that some data is lost or thrown away, to create a smaller more manageable file. You can choose to have a maximised compression which will be a minimum loss of data, and a higher quality is maintained. You can choose to do a heavier compression which will make the pixels in the image more noticeable. Raw images go through lossless compression which maintains all the data, no data is thrown away, therefore it does not degrade the quality of the images..

Sharpening

Sharpening increases the contrast along the edges. As raw files have not had any sharpening applied, you get to choose the level of sharpening applied to the image. In a JPEG file sharpening has already occurred via the camera software. When sharpening is applied to a JPEG it may make the JPEG squares seem more visible, which is not usually the effect you are affter with sharpening. Sharpening a JPEG file multiple times causes degradation in the image every time it is done. You will not have as many options for sharpening a JPEG image file as you will a raw file. When applying sharpening to a raw image a new file is created, therefore no quality is lost on the original file. You can make as many adjustments as you like with a raw file without degrading it.

Processing time

Raw images take longer to process than a JPEG. However, if you are after higher quality image it is worth the extra effort that you put in with a raw image.

Generally, if the images are only for personal use and you don’t really need them to be of the highest quality, a JPEG will do fine and will be ready to use and viewed in any viewer straight away. Raw images do take a bit more work and will require you to edit the images yourself in raw converter software, however the quality of the output will be much higher. It’s best to assess for yourself whether you need raw or JPEG images. When quality is the key, personally I would go raw, you have more flexibility to create the best image possible.