What if I rephrase the question: Is there a way for me to compress a plain red image using the same compression method as reference.jpg using libjpeg-turbo? The resulting red image should have the exact same hex code between FFD8 and FFDA as reference.jpg.
在2023年6月29日星期四 UTC+8 04:56:28<DRC> 写道： > Even if you use the identical compression method, there is no way to > perfectly simulate a JPEG reference image unless you can obtain the > original pixels that were used to generate the reference image. The term > "re-compress" means that you have to decompress first, so you will incur > generational loss, as I mentioned below. You can't perfectly duplicate the > JPEG image data (the data after the SOS marker) from the metadata and > decompressed pixels of a reference JPEG image. You can perfectly duplicate > the JPEG image data from the metadata of a reference JPEG image if you have > access to the original pixels that were used to generate the reference > image, but your messages imply that you don't. That means that what you're > trying to do is impossible. > On 6/28/23 4:46 PM, Hugh Shaw wrote: > > I think you may have misunderstood my intention. What I hope to achieve is > to compress an image using the same compression method as reference.jpg, > perfectly simulating it. In my understanding, the hex code of a JPEG > includes information such as DQT, SOF, and DHT. I wonder if I can use this > information to re-compress an image and generate output.jpg. Theoretically, > the hex code between FFD8 and FFDA should be identical in output.jpg and > reference.jpg, and the compression data after SOS should also be calculated > based on information such as DQT, SOF, and DHT. I hope to use libjpeg-turbo > to implement this function. It seems that jpegtran cannot achieve this. > > > 在2023年6月29日星期四 UTC+8 04:19:58<DRC> 写道： > >> I can only barely comprehend what you are trying to do or why, but unless >> the reference image is a lossless JPEG (I assume not, if it has a DQT), any >> decompression/compression cycle will result in generational loss. Thus, >> you cannot exactly regenerate a lossy reference JPEG image unless you have >> the original uncompressed image that was used to generate the reference >> image in the first place. Once a JPEG image is generated, then some of >> that original data is lost. The best you can do is copy the DCT blocks (in >> the frequency domain) from one JPEG container to another, which is what >> jpegtran does. That avoids a decompression/recompression cycle and thus >> avoids generational loss, so the transformed JPEG image has no additional >> loss relative to the reference JPEG image. However, there are limits to >> what you can do in the frequency domain. You can reorder the DCT blocks; >> spatially transpose, rotate, or flip the blocks; remove or change the order >> of some of the component planes (e.g. convert color to grayscale); negate >> the coefficients (photo negative); re-quantize the coefficients (lower the >> effective JPEG quality); change the entropy algorithm (e.g. convert >> baseline to progressive or arithmetic); add restart markers; crop the image >> (by discarding certain blocks); wipe an image region (by greying out >> certain blocks); drop another image into the source image (by replacing >> certain blocks); or remove metadata. >> On 6/28/23 3:59 PM, Hugh Shaw wrote: >> >> I have a specific requirement I need help with and hope to get assistance >> from experts in the field. I have learned that for the same compression >> algorithm, the compression fingerprints are consistent. This means that the >> data from FF D8 to just before the scan line FF DA are always identical. >> Based on this information, I would like to be able to duplicate the >> compression fingerprint of one image and apply it to another. >> >> Specifically, I need to accomplish two things: >> >> First, use the perfectly compressed fingerprint from reference.jpg to >> compress input.jpg and generate output.jpg. Second, make sure that the DQT, >> SOF, and DHT information in output.jpg is exactly the same (including hex >> codes) as in reference.jpg. I have already ensured that the pixel >> dimensions of input.jpg and reference.jpg are the same. >> >> I have attempted to code a solution, as shown below, which involves >> manually copying the quantization and Huffman tables, copying critical >> parameters, and applying the compression and decompression. However, the >> resulting output.jpg differs in hex code from the reference image, even >> though the dimensions are the same. >> >> *Due to lenght limitations, I can only include the code I tried in the >> attachment* >> >> I am unsure what the issue is and would appreciate any guidance in >> resolving this problem. 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