post processing - Why RAW to JPG creates more noise in image in Adobe Photoshop?

When i click image at that time Raw format doesn't contain any noise, but when i opened into Adobe Photosho CC 2017 version and after modifying raw data and open to ps ans save as jpg gives colors noise.

why happening this ? is there any raw editor better than PS ?

Answer

The way that JPEG works. Your going from an uncompressed format to a compressed format.

How JPEG Works

"Downsampling is simply the process of reducing the chroma values by some factor (and therefore is the first step in losing information). In the JPEG format, there are three accepted possibilities: no downsampling at all, dividing the chroma values horizontally by two, or dividing the chroma values both horizontally or vertically by two.

The next step is to split the downsampled pixels in the image into 8 x 8 blocks. Each colour component is split up separately, and each component sample goes through the same process in what follows. Note that on many occasions, the size of the image will not be a simple multiple of eight pixels in either direction. This can result in some pixel artefacts being created along the right and bottom sides of a JPEG picture.

The next step is fun, but puzzling. Each 8 x 8 block is converted into another matrix using a Discrete Cosine Transform (DCT). This transform, which is similar to a Fourier transform, analyses the frequencies of the original values along each row and column using a set of cosine waves oscillating at different frequencies and amplitudes. The reason for doing this is that the higher frequencies can be minimized or zeroed out since we do not perceive their loss as acutely as the more energetic lower frequencies.

This converted matrix is then quantised. This is the main lossy part of the algorithm and the stage where we minimise the higher frequencies over the lower frequencies. One major result of this quantisation is that many higher DCT coefficients are zeroed out, making them extremely compressible in the next step.

The quantisation is accomplished by a set of 8 x 8 matrices, each one representing a different 'quality factor' for the JPEG image. Each cell is divided by the corresponding cell in the quantisation matrix and the result rounded (another lossy operation). Note that this does not involve matrix multiplication in the mathematical sense of the phrase.

Finally, the resulting quantised matrix is encoded using Huffman compression. To make the most use of the way the values in the matrix seem to radiate out from the top-left corner, the values are encoded not across each row for all rows but in a zig-zag pattern. This means that the zero cells tend to appear at the end of the zig-zag chain and therefore can be ruthlessly compressed (in fact, there's a special code that indicates that all remaining cell values are zero in the 8 x 8 block)."

http://www.techradar.com/news/computing/all-you-need-to-know-about-jpeg-compression-586268/2