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Fix parsing of JPEG headers #175

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merged 2 commits into from
Sep 20, 2018
Merged

Fix parsing of JPEG headers #175

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0b69b5f
Fix parsing of JPEG headers for host decoder, add more tests
JanuszL Sep 18, 2018
989e7c0
Update comment for jpeg.cc code inspiration
JanuszL Sep 20, 2018
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48 changes: 20 additions & 28 deletions dali/image/jpeg.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -54,40 +54,32 @@ void PrintSubsampling(int sampling) {
}
#endif // DALI_USE_JPEG_TURBO

// Slightly modified from https://github.com/apache/incubator-mxnet/blob/master/plugin/opencv/cv_api.cc
// http://www.64lines.com/jpeg-width-height
// Gets the JPEG size from the array of data passed to the function, file reference: http://www.obrador.com/essentialjpeg/headerinfo.htm
// Based on https://github.com/scardine/image_size
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The code seems only very slightly modified from the previous version, so I would put both references here (image_size and mxnet)

bool get_jpeg_size(const uint8 *data, size_t data_size, int *height, int *width) {
// Check for valid JPEG image
unsigned int i = 0; // Keeps track of the position within the file
if (data[i] == 0xFF && data[i+1] == 0xD8 && data[i+2] == 0xFF && data[i+3] == 0xE0) {
if (data[i] == 0xFF && data[i+1] == 0xD8) {
i += 4;
// Check for valid JPEG header (null terminated JFIF)
if (data[i+2] == 'J' && data[i+3] == 'F' && data[i+4] == 'I'
&& data[i+5] == 'F' && data[i+6] == 0x00) {
// Retrieve the block length of the first block since
// the first block will not contain the size of file
uint16_t block_length = data[i] * 256 + data[i+1];
while (i < data_size) {
i+=block_length; // Increase the file index to get to the next block
if (i >= data_size) return false; // Check to protect against segmentation faults
if (data[i] != 0xFF) return false; // Check that we are truly at the start of another block
if (data[i+1] == 0xC0) {
// 0xFFC0 is the "Start of frame" marker which contains the file size
// The structure of the 0xFFC0 block is quite simple
// [0xFFC0][ushort length][uchar precision][ushort x][ushort y]
*height = data[i+5]*256 + data[i+6];
*width = data[i+7]*256 + data[i+8];
return true;
} else {
i+=2; // Skip the block marker
block_length = data[i] * 256 + data[i+1]; // Go to the next block
}
// Retrieve the block length of the first block since
// the first block will not contain the size of file
uint16_t block_length = data[i] * 256 + data[i+1];
while (i < data_size) {
i+=block_length; // Increase the file index to get to the next block
if (i >= data_size) return false; // Check to protect against segmentation faults
if (data[i] != 0xFF) return false; // Check that we are truly at the start of another block
if (data[i+1] >= 0xC0 && data[i+1] <= 0xC3) {
// 0xFFC0 is the "Start of frame" marker which contains the file size
// The structure of the 0xFFC0 block is quite simple
// [0xFFC0][ushort length][uchar precision][ushort x][ushort y]
*height = data[i+5]*256 + data[i+6];
*width = data[i+7]*256 + data[i+8];
return true;
} else {
i+=2; // Skip the block marker
block_length = data[i] * 256 + data[i+1]; // Go to the next block
}
return false; // If this point is reached then no size was found
} else {
return false; // Not a valid JFIF string
}
return false; // If this point is reached then no size was found
} else {
return false; // Not a valid SOI header
}
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8 changes: 5 additions & 3 deletions dali/test/python/test_data_containers.py
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Expand Up @@ -23,11 +23,13 @@ class CommonPipeline(Pipeline):
def __init__(self, batch_size, num_threads, device_id):
super(CommonPipeline, self).__init__(batch_size, num_threads, device_id)

self.decode = ops.nvJPEGDecoder(device = "mixed", output_type = types.RGB)
self.decode_gpu = ops.nvJPEGDecoder(device = "mixed", output_type = types.RGB)
self.decode_host = ops.HostDecoder(device = "cpu", output_type = types.RGB)

def base_define_graph(self, inputs, labels):
images = self.decode(inputs)
return (images, labels)
images_gpu = self.decode_gpu(inputs)
images_host = self.decode_host(inputs)
return (images_gpu, images_host, labels)

class MXNetReaderPipeline(CommonPipeline):
def __init__(self, batch_size, num_threads, device_id, num_gpus, data_paths):
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