Is there a uncompressed format to PNG?

Question

As we know PNG image format being the lossless format for image files. Compared to lossless audio file formats such as FLAC for example: When I decompress it, I get uncompressed .WAV file format.

So I'm wondering which uncompressed format does PNG compresses? Is it the Bitmap file format?

Answer 1

FLAC is not compressed .WAV.

• FLAC is a format that stores and compress digital waveforms (PCM) without loss.
• WAV is a format that store PCM data without compression.

What I'm saying is that when you uncompressed a FLAC, you're not magically getting a .WAV file. Rather, the program you're using is decoding the PCM data and writing it back into the .WAV format just because it's the most common format. Since both formats are lossless, there's no loss in this transition, but the PCM waveform could just as well be written back to other lossless formats: such as Apple AIFF and CD audio.

Due to the age and popularity of the .WAV format in both consumer and professional, it just happens - by tradition and device support - to be lowest common denominator format, but wouldn't necessarily have to be.

I hope this provides a new angle to your question.

Similarly, a lossless image is a raster graphic, or bitmap, but bitmap data is not necessarily linked to the .BMP format, which is just specific way for storing bitmap data. Just like .WAVs, the popular usage of BMP mainly derive out of their simplicity (well documented, don't support lossy content, etc), and having been around for a while.

Other common lossless formats that are also uncompressed include:

• TIFF has been around for a long time in business applications, but it is a more flexible/complex format that can be both lossy and lossless
• RAW which is found in many digital cameras can also be lossless.

In summary, there are no original format for either "audio" or "image" data, anyone could store it anyway they wish. What we have are common file formats and softwares that know how to translate between them.

To answer your question, it seems .BMP is not as much the de facto standard that .WAV got the be in the audio world. Whether the uncompressed format of choice is BMP, TIFF or RAW (or others) will depend on the type of application/business.

Answer 2

What @mtone wrote needs a few words to clarify things:

• .WAV is not a format. It's a container for other formats. You can put inside a WAV container many different audio formats. You can create a .WAV file with an mp3 song inside it. Therefore .WAV can have (not be) both lossless and lossy.
• .TIFF is also not a format but a container. You can place jpeg images inside a TIF. So, just like mtone wrote, it can have lossless and lossy formats inside.
• There isn't one RAW format. Different cameras use different raw formats. Canon uses .CRW and .CR2, Nikon uses .NEF and .NRW and so on.
• Besides "camera raw" there are also "real" raw formats that were used long before digital cameras were invented. "Real" raw formats are so raw they contain just the pixels, nothing else. Many games used raw formats in the past. How did these work? A game creator decided they need 640x480 pixel images with 24 bit color pixels and nothing else. So they saved these images without any header or metadata into files. Such images were exactly 640x480x3 bytes in size. Another game creator decided his/her game needs 320x200 images with 8 bits per pixel in grayscale so all the images for this game are exactly 320x200 bytes long in size. This is the rawest possible way to store images.
• .BMP is a format (not a container) but can be compressed. Losslessy using RLE method but can be compressed. So it's actually not that simple format everyone thinks it is. It's popular and widely used just because Microsoft made it popular and it was easy to implement partial BMP saving/loading. However there doesn't exist a program that could read and save every possible BMP image. That's how complicated this format is.