What is a RAW format image?

What is a RAW format file?

RAW file is a kind of raw information that records the digital camera sensor, and also records some raw data (Metadata, such as IS0 settings, shutter speed, aperture value, white balance, etc.) generated by the camera. ) file. RAW is an unprocessed and uncompressed format. RAW can be conceptualized as "original image encoding data" or more vividly as "digital negative".

The biggest advantage of RAW is that it preserves the original CCD data and puts more freedom in the hands of users. The most original and authentic information is recorded without modification or alteration, leaving broad maneuverability for post-production.

How to obtain RAW format files?

You must have a camera that supports RAW format to create RAW format files. Most SLR cameras support shooting in RAW format, but you need to set the camera to save in RAW format before shooting. Different brands of cameras have different suffixes for the RAW format files they output. Most camera manufacturers provide software that can process the RAW files they output. As the RAW format is valued by digital photographers and post-production designers, a variety of professional RAW processing software has appeared on the market. They can support RAW format files output by cameras of various brands and models, and also have more professional functions. In the following article, several senior moderators of the professional imaging post-production website Singseism (www.swcool.com): Jingxiaxia, Xiaoding, Orange, Liuchao, and Chenchen will explain in detail the current six mainstream RAW processing software. Let me introduce to you.

What items can be adjusted in RAW?

1. White balance: including color temperature and hue. "Color temperature" is the white balance setting, which can be adjusted in the camera when shooting (valid for both JPEG and RAW), but when shooting JPEG, once it is set Once the white balance is set, it cannot be changed afterwards. And if you don’t have a color temperature meter, don’t think you can set it accurately. The screen behind the camera cannot accurately judge whether the color temperature is set accurately. If you want to change it afterwards, you can only change the color in PS (required Know: Changing various adjustments such as brightness and color in PS will cause a certain loss of image details. The greater the change and the more times the changes are made, the greater the loss of image details); but when using RAW! Format, adjusting the color temperature during conversion is equivalent to resetting the white balance during shooting (like a continuation of the photography process), and the adjustable range is very large, which is a "re-creation" of photography. The range of "tone" adjustment is much larger than the range of changes in the camera!

2. Change of exposure: It can be changed by plus or minus 4 times, which is another photography re-creation. With the layer mask in PS, you can find rich levels in almost all areas of the picture on the same picture. I have demonstrated to many people (including at school) how a picture with a large light ratio can display the brightest and darkest colors. The area can be controlled at the same time and the level is well controlled. However, if the JPEG format is overexposed and a "dead white" area appears, it will be completely boring. This method is often used in: backlight photography under strong sunlight, photography under stage spotlights, and many other aspects.

3. Make separate adjustments for dark and bright parts. Contrast and saturation can be adjusted;

4. Sharpness adjustment: Its adjustment is sharper than that in PS. The transformation is much more natural, and with moderate adjustments, there will be no trace at all afterwards, but the clarity will be improved a lot!

All images taken by digital cameras have the problem of "softness" and are not clear enough. When shooting in JPEG format, the camera usually quietly sharpens to a certain extent, and the effect is very natural (professional cameras silently The sharpening range is relatively small, such as Canon's 1 series, Nikon's D2X, etc.). If you feel it is not enough, you can add more in the camera (professional cameras can adjust the range to a large extent, such as Canon's 1D, not only Adjust the degree of sharpening, and you can adjust the area affected by sharpening), but it is far better than shooting in RAW and then changing it in the conversion window. (The camera's sharpening adjustment does not work on RAW format files.)

5. Processing of noise and purple edges - this is something that Canon's DPP software does not have. . Some people say that pictures taken with RAW have more noise than JPEG. This is because the camera performs certain processing on JPEG, and RAW is not an image format, but a collection of original image information, which is processed by the PS conversion window. , the effect is much better than using JPEG shooting and relying on camera processing!

6. Processing of vignetting: Wide-angle lenses sometimes lose light in the four corners. For example, Canon's 17-85mm lens is a lens produced for small digital chips and can only be used on 1.6x Canon cameras. (Currently it can only be used on three cameras: 300D, 350D, and 20D). It has a vignetting problem at the wide-angle end. This weakness can be completely eliminated through the processing of a RAW converter.

How to choose between RAW format, TIFF format and JPEG format?

The advantage of the JPEG format is that its file capacity is relatively small. More photos can be stored in the JPEG format. The storage speed of the JPEG format is quite fast, especially compared to the RAW format, and it can capture the moment of the shot. In terms of compatibility, it is also the best among several formats. More than 95% of graphics processing software can directly open pictures in JPEG format.

The shortcomings of the JPEG format are more obvious. Since the photos taken have been adjusted internally by the camera, information such as color temperature, color balance, image sharpness, etc. have been fixed. Post-adjustment can only be done through professional graphics software. TIFF format is a non-distorted compression format (up to 2-3 times compression ratio). This kind of compression is the compression of the file itself, that is, certain repeated information in the file is recorded in a special way. The file can be completely restored and the original image color and level can be maintained. The advantage is that the image quality is better and the compatibility is better. RAW format is good, but takes up a lot of space.

RAW format is a proprietary format for each camera manufacturer, and these files are losslessly compressed. When a digital camera performs an exposure, the CCD (or CMOS) sensor will record the amount of light at each pixel in terms of level, and then the digital camera will convert these electrical signals into corresponding digital signals, which are generally recorded as 12 bit or 14-bit data. If a digital camera records 12-bit or 14-bit data, it means that each pixel has 4096 or 16384 different brightness levels. If RAW is selected as the file storage format, it can be saved later through the RAW conversion tool. 16-bit TIFF or PSD format for output, and the 12- or 14-bit data recorded by digital cameras can also be expanded to the full 16-bit space. But if you choose the JPEG format to store the file, the software in the camera will convert it to 8-bit mode, which means it can only record 256 brightness levels. Of course, the biggest advantage of the RAW format in actual use is that during conversion, the original recorded data on the CCD (or CMOS) sensor can be processed for exposure compensation, color balance, etc., and the image quality will never be destroyed.

RAW has obvious advantages, but its disadvantages are also clear. First of all, RAW format pictures require related supporting software to export photos. Secondly, the storage speed is relatively slow and the file capacity is relatively large. However, it is slightly faster than TIFF format because the original unit data of RAW only needs 12 bits or more. 14-bit data storage, while the TIFF format requires 16-bit data storage, which makes the size of the RAW format much smaller than the TIFF format.

As can be seen from the above, although the RAW format has many advantages in post-production, it also has the disadvantage of large files and slow speed. Therefore, we should not regard the RAW format as a dead dogma and should base it on our own actual conditions. Flexible choice according to the situation. If you need to make post-adjustments to your work and have very high image quality requirements, you should choose RAW format to shoot, then make the necessary post-adjustments through RAW software and save it in TIFF format (Camera Raw can be transferred directly to Photoshop after adjustment) Editing), and then use Adobe Photoshop and other software for post-production design and creation as needed, and finally output it into PSD format, TIFF format or JPEG format according to the actual standard needs. This can minimize the loss of image quality and proceed more rigorously. Quality control.